Simplify the fee extensions.

I added shared base classes to all of the Fee extension types that
make it possible to fully ignore the version in the flows. (You
ask for a FeeCreateCommandExtension, for example, and you get one
without having to worry about which). This is an improvement over
the old code that asked you to provide a list of possible fee
extensions and then ask for the first one in preference order.

As part of this I was able to make the Fee implementation a bit
simpler as well.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=137992390

java/google/registry/flows/ExtensionManager.java

@@ -14,12 +14,16 @@
 
 package google.registry.flows;
 
+import static com.google.common.collect.Iterables.any;
 import static com.google.common.collect.Sets.difference;
 import static com.google.common.collect.Sets.intersection;
 import static google.registry.model.domain.fee.Fee.FEE_EXTENSION_URIS;
 import static google.registry.model.eppcommon.ProtocolDefinition.ServiceExtension.getCommandExtensionUri;
 
 import com.google.common.base.Joiner;
+import com.google.common.base.Predicate;
+import com.google.common.collect.FluentIterable;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import google.registry.flows.EppException.CommandUseErrorException;
 import google.registry.flows.EppException.SyntaxErrorException;
@@ -30,7 +34,6 @@ import google.registry.model.domain.metadata.MetadataExtension;
 import google.registry.model.eppinput.EppInput;
 import google.registry.model.eppinput.EppInput.CommandExtension;
 import google.registry.util.FormattingLogger;
-import java.util.Collection;
 import java.util.Set;
 import javax.inject.Inject;
 
@@ -49,8 +52,6 @@ public final class ExtensionManager {
 
   private final ImmutableSet.Builder<Class<? extends CommandExtension>> implementedBuilder =
       new ImmutableSet.Builder<>();
-  private final ImmutableSet.Builder<ImmutableSet<?>> implementedGroupsBuilder =
-      new ImmutableSet.Builder<>();
 
   @Inject EppInput eppInput;
   @Inject SessionMetadata sessionMetadata;
@@ -64,12 +65,6 @@ public final class ExtensionManager {
     implementedBuilder.add(extension);
   }
 
-  public <T extends CommandExtension> void registerAsGroup(
-      Collection<Class<? extends T>> extensions) {
-    implementedBuilder.addAll(extensions);
-    implementedGroupsBuilder.add(ImmutableSet.copyOf(extensions));
-  }
-
   public void validate() throws EppException {
     ImmutableSet.Builder<Class<? extends CommandExtension>> suppliedBuilder =
         new ImmutableSet.Builder<>();
@@ -79,27 +74,12 @@ public final class ExtensionManager {
     ImmutableSet<Class<? extends CommandExtension>> suppliedExtensions = suppliedBuilder.build();
     ImmutableSet<Class<? extends CommandExtension>> implementedExtensions =
         implementedBuilder.build();
-    ImmutableSet<ImmutableSet<?>> implementedExtensionGroups =
+    ImmutableList<CommandExtension> suppliedExtensionInstances =
-        implementedGroupsBuilder.build();
+        eppInput.getCommandWrapper().getExtensions();
-    checkForDuplicateExtensions(suppliedExtensions, implementedExtensionGroups);
     checkForUndeclaredExtensions(suppliedExtensions);
     checkForRestrictedExtensions(suppliedExtensions);
-    checkForUnimplementedExtensions(suppliedExtensions, implementedExtensions);
+    checkForDuplicateExtensions(suppliedExtensionInstances, suppliedExtensions);
-  }
+    checkForUnimplementedExtensions(suppliedExtensionInstances, implementedExtensions);
-
-  private void checkForDuplicateExtensions(
-      ImmutableSet<Class<? extends CommandExtension>> suppliedExtensions,
-      ImmutableSet<ImmutableSet<?>> implementedExtensionGroups)
-          throws UnsupportedRepeatedExtensionException {
-    if (suppliedExtensions.size() < eppInput.getCommandWrapper().getExtensions().size()) {
-      throw new UnsupportedRepeatedExtensionException();
-    }
-    // No more than one extension in an extension group can be present.
-    for (ImmutableSet<?> group : implementedExtensionGroups) {
-      if (intersection(suppliedExtensions, group).size() > 1) {
-        throw new UnsupportedRepeatedExtensionException();
-      }
-    }
   }
 
   private void checkForUndeclaredExtensions(
@@ -134,22 +114,39 @@ public final class ExtensionManager {
     }
   }
 
-  private void checkForUnimplementedExtensions(
+  private static void checkForDuplicateExtensions(
-      ImmutableSet<Class<? extends CommandExtension>> suppliedExtensions,
+      ImmutableList<CommandExtension> suppliedExtensionInstances,
       ImmutableSet<Class<? extends CommandExtension>> implementedExtensions)
-          throws UnimplementedExtensionException {
+          throws UnsupportedRepeatedExtensionException {
-    Set<Class<? extends CommandExtension>> unimplementedExtensions =
+    for (Class<? extends CommandExtension> implemented : implementedExtensions) {
-        difference(suppliedExtensions, implementedExtensions);
+      if (FluentIterable.from(suppliedExtensionInstances).filter(implemented).size() > 1) {
-    if (!unimplementedExtensions.isEmpty()) {
+        throw new UnsupportedRepeatedExtensionException();
-      logger.infofmt("Unimplemented extensions: %s", unimplementedExtensions);
+      }
-      throw new UnimplementedExtensionException();
     }
   }
 
-  /** Unsupported repetition of an extension. */
+  private static void checkForUnimplementedExtensions(
-  static class UnsupportedRepeatedExtensionException extends SyntaxErrorException {
+      ImmutableList<CommandExtension> suppliedExtensionInstances,
-    public UnsupportedRepeatedExtensionException() {
+      ImmutableSet<Class<? extends CommandExtension>> implementedExtensionClasses)
-      super("Unsupported repetition of an extension");
+          throws UnimplementedExtensionException {
+    ImmutableSet.Builder<Class<? extends CommandExtension>> unimplementedExtensionsBuilder =
+        new ImmutableSet.Builder<>();
+    for (final CommandExtension instance : suppliedExtensionInstances) {
+      if (!any(
+          implementedExtensionClasses,
+          new Predicate<Class<? extends CommandExtension>>() {
+            @Override
+            public boolean apply(Class<? extends CommandExtension> implementedExtensionClass) {
+              return implementedExtensionClass.isInstance(instance);
+            }})) {
+        unimplementedExtensionsBuilder.add(instance.getClass());
+      }
+    }
+    ImmutableSet<Class<? extends CommandExtension>> unimplementedExtensions =
+        unimplementedExtensionsBuilder.build();
+    if (!unimplementedExtensions.isEmpty()) {
+      logger.infofmt("Unimplemented extensions: %s", unimplementedExtensions);
+      throw new UnimplementedExtensionException();
     }
   }
 
@@ -160,4 +157,11 @@ public final class ExtensionManager {
             Joiner.on(", ").join(undeclaredUris)));
     }
   }
+
+  /** Unsupported repetition of an extension. */
+  static class UnsupportedRepeatedExtensionException extends SyntaxErrorException {
+    public UnsupportedRepeatedExtensionException() {
+      super("Unsupported repetition of an extension");
+    }
+  }
 }

java/google/registry/flows/domain/DomainAllocateFlow.java

@@ -30,7 +30,6 @@ import static google.registry.flows.domain.DomainFlowUtils.validateSecDnsExtensi
 import static google.registry.flows.domain.DomainFlowUtils.verifyUnitIsYears;
 import static google.registry.model.EppResourceUtils.createDomainRoid;
 import static google.registry.model.EppResourceUtils.loadDomainApplication;
-import static google.registry.model.domain.fee.Fee.FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.model.registry.label.ReservedList.matchesAnchorTenantReservation;
 import static google.registry.pricing.PricingEngineProxy.getDomainCreateCost;
@@ -63,7 +62,7 @@ import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.allocate.AllocateCreateExtension;
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import google.registry.model.domain.fee.FeeCreateCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import google.registry.model.domain.flags.FlagsCreateCommandExtension;
 import google.registry.model.domain.launch.ApplicationStatus;
@@ -118,11 +117,11 @@ public class DomainAllocateFlow implements TransactionalFlow {
   @Override
   public final EppResponse run() throws EppException {
     extensionManager.register(
+        FeeCreateCommandExtension.class,
         SecDnsCreateExtension.class,
         FlagsCreateCommandExtension.class,
         MetadataExtension.class,
         AllocateCreateExtension.class);
-    extensionManager.registerAsGroup(FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     verifyIsSuperuser();
@@ -374,8 +373,8 @@ public class DomainAllocateFlow implements TransactionalFlow {
       DateTime now, Registry registry, int years) throws EppException {
     EppCommandOperations commandOperations = TldSpecificLogicProxy.getCreatePrice(
         registry, targetId, clientId, now, years, eppInput);
-    FeeTransformCommandExtension feeCreate =
+    FeeCreateCommandExtension feeCreate =
-        eppInput.getFirstExtensionOfClasses(FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeCreateCommandExtension.class);
     return (feeCreate == null)
         ? null
         : ImmutableList.of(createFeeCreateResponse(feeCreate, commandOperations));

java/google/registry/flows/domain/DomainApplicationCreateFlow.java

@@ -38,7 +38,6 @@ import static google.registry.flows.domain.DomainFlowUtils.verifyRegistryStateAl
 import static google.registry.flows.domain.DomainFlowUtils.verifySignedMarks;
 import static google.registry.flows.domain.DomainFlowUtils.verifyUnitIsYears;
 import static google.registry.model.EppResourceUtils.createDomainRoid;
-import static google.registry.model.domain.fee.Fee.FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.index.DomainApplicationIndex.loadActiveApplicationsByDomainName;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.model.registry.label.ReservedList.matchesAnchorTenantReservation;
@@ -65,6 +64,7 @@ import google.registry.model.domain.DomainApplication;
 import google.registry.model.domain.DomainCommand.Create;
 import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.Period;
+import google.registry.model.domain.fee.FeeCreateCommandExtension;
 import google.registry.model.domain.fee.FeeTransformCommandExtension;
 import google.registry.model.domain.flags.FlagsCreateCommandExtension;
 import google.registry.model.domain.launch.ApplicationStatus;
@@ -172,11 +172,11 @@ public final class DomainApplicationCreateFlow implements TransactionalFlow {
   @Override
   public final EppResponse run() throws EppException {
     extensionManager.register(
+        FeeCreateCommandExtension.class,
         SecDnsCreateExtension.class,
         FlagsCreateCommandExtension.class,
         MetadataExtension.class,
         LaunchCreateExtension.class);
-    extensionManager.registerAsGroup(FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     DateTime now = ofy().getTransactionTime();
@@ -212,8 +212,8 @@ public final class DomainApplicationCreateFlow implements TransactionalFlow {
         verifyNotReserved(domainName, isSunriseApplication);
       }
     }
-    FeeTransformCommandExtension feeCreate =
+    FeeCreateCommandExtension feeCreate =
-        eppInput.getFirstExtensionOfClasses(FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeCreateCommandExtension.class);
     validateFeeChallenge(targetId, tld, now, feeCreate, commandOperations.getTotalCost());
     SecDnsCreateExtension secDnsCreate =
         validateSecDnsExtension(eppInput.getSingleExtension(SecDnsCreateExtension.class));

java/google/registry/flows/domain/DomainApplicationUpdateFlow.java

@@ -39,7 +39,6 @@ import static google.registry.flows.domain.DomainFlowUtils.verifyApplicationDoma
 import static google.registry.flows.domain.DomainFlowUtils.verifyClientUpdateNotProhibited;
 import static google.registry.flows.domain.DomainFlowUtils.verifyNotInPendingDelete;
 import static google.registry.model.EppResourceUtils.loadDomainApplication;
-import static google.registry.model.domain.fee.Fee.FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 
 import com.google.common.base.Optional;
@@ -138,7 +137,6 @@ public class DomainApplicationUpdateFlow implements TransactionalFlow {
         LaunchUpdateExtension.class,
         MetadataExtension.class,
         SecDnsUpdateExtension.class);
-    extensionManager.registerAsGroup(FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     DateTime now = ofy().getTransactionTime();

java/google/registry/flows/domain/DomainCheckFlow.java

@@ -23,7 +23,6 @@ import static google.registry.flows.domain.DomainFlowUtils.validateDomainName;
 import static google.registry.flows.domain.DomainFlowUtils.validateDomainNameWithIdnTables;
 import static google.registry.flows.domain.DomainFlowUtils.verifyNotInPredelegation;
 import static google.registry.model.EppResourceUtils.checkResourcesExist;
-import static google.registry.model.domain.fee.Fee.FEE_CHECK_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.index.DomainApplicationIndex.loadActiveApplicationsByDomainName;
 import static google.registry.model.registry.label.ReservationType.UNRESERVED;
 import static google.registry.pricing.PricingEngineProxy.isDomainPremium;
@@ -111,8 +110,7 @@ public final class DomainCheckFlow implements Flow {
 
   @Override
   public EppResponse run() throws EppException {
-    extensionManager.register(LaunchCheckExtension.class);
+    extensionManager.register(FeeCheckCommandExtension.class, LaunchCheckExtension.class);
-    extensionManager.registerAsGroup(FEE_CHECK_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     List<String> targetIds = ((Check) resourceCommand).getTargetIds();
@@ -177,7 +175,7 @@ public final class DomainCheckFlow implements Flow {
   private ImmutableList<? extends ResponseExtension> getResponseExtensions(
       ImmutableMap<String, InternetDomainName> domainNames, DateTime now) throws EppException {
     FeeCheckCommandExtension<?, ?> feeCheck =
-        eppInput.getFirstExtensionOfClasses(FEE_CHECK_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeCheckCommandExtension.class);
     if (feeCheck == null) {
       return null;  // No fee checks were requested.
     }
@@ -185,7 +183,7 @@ public final class DomainCheckFlow implements Flow {
         new ImmutableList.Builder<>();
     for (FeeCheckCommandExtensionItem feeCheckItem : feeCheck.getItems()) {
       for (String domainName : getDomainNamesToCheckForFee(feeCheckItem, domainNames.keySet())) {
-        FeeCheckResponseExtensionItem.Builder builder = feeCheckItem.createResponseBuilder();
+        FeeCheckResponseExtensionItem.Builder<?> builder = feeCheckItem.createResponseBuilder();
         handleFeeRequest(
             feeCheckItem,
             builder,

java/google/registry/flows/domain/DomainCreateFlow.java

@@ -36,7 +36,6 @@ import static google.registry.flows.domain.DomainFlowUtils.verifyPremiumNameIsNo
 import static google.registry.flows.domain.DomainFlowUtils.verifySignedMarks;
 import static google.registry.flows.domain.DomainFlowUtils.verifyUnitIsYears;
 import static google.registry.model.EppResourceUtils.createDomainRoid;
-import static google.registry.model.domain.fee.Fee.FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.index.DomainApplicationIndex.loadActiveApplicationsByDomainName;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.model.registry.label.ReservedList.matchesAnchorTenantReservation;
@@ -70,7 +69,7 @@ import google.registry.model.domain.DomainCommand.Create;
 import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.Period;
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import google.registry.model.domain.fee.FeeCreateCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import google.registry.model.domain.flags.FlagsCreateCommandExtension;
 import google.registry.model.domain.launch.LaunchCreateExtension;
@@ -168,11 +167,11 @@ public class DomainCreateFlow implements TransactionalFlow {
   @Override
   public final EppResponse run() throws EppException {
     extensionManager.register(
+        FeeCreateCommandExtension.class,
         SecDnsCreateExtension.class,
         FlagsCreateCommandExtension.class,
         MetadataExtension.class,
         LaunchCreateExtension.class);
-    extensionManager.registerAsGroup(FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     DateTime now = ofy().getTransactionTime();
@@ -199,8 +198,8 @@ public class DomainCreateFlow implements TransactionalFlow {
     if (hasSignedMarks) {
       verifySignedMarksAllowed(tldState, isAnchorTenant);
     }
-    FeeTransformCommandExtension feeCreate =
+    FeeCreateCommandExtension feeCreate =
-        eppInput.getFirstExtensionOfClasses(FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeCreateCommandExtension.class);
     EppCommandOperations commandOperations = TldSpecificLogicProxy.getCreatePrice(
         registry, targetId, clientId, now, years, eppInput);
     validateFeeChallenge(
@@ -423,7 +422,7 @@ public class DomainCreateFlow implements TransactionalFlow {
   }
 
   private ImmutableList<FeeTransformResponseExtension> createResponseExtensions(
-      FeeTransformCommandExtension feeCreate, EppCommandOperations commandOperations) {
+      FeeCreateCommandExtension feeCreate, EppCommandOperations commandOperations) {
     return (feeCreate == null)
         ? null
         : ImmutableList.of(createFeeCreateResponse(feeCreate, commandOperations));

java/google/registry/flows/domain/DomainFlowUtils.java

@@ -584,7 +584,7 @@ public class DomainFlowUtils {
    */
   static void handleFeeRequest(
       FeeQueryCommandExtensionItem feeRequest,
-      FeeQueryResponseExtensionItem.Builder builder,
+      FeeQueryResponseExtensionItem.Builder<?, ?> builder,
       InternetDomainName domain,
       String clientId,
       @Nullable CurrencyUnit topLevelCurrency,
@@ -617,7 +617,7 @@ public class DomainFlowUtils {
         .setPeriod(feeRequest.getPeriod())
         .setClass(TldSpecificLogicProxy.getFeeClass(domainNameString, now).orNull());
 
-    List<Fee> fees = ImmutableList.of();
+    ImmutableList<Fee> fees = ImmutableList.of();
     switch (feeRequest.getCommandName()) {
       case CREATE:
         if (isReserved(domain, isSunrise)) {  // Don't return a create price for reserved names.

java/google/registry/flows/domain/DomainRenewFlow.java

@@ -27,7 +27,6 @@ import static google.registry.flows.domain.DomainFlowUtils.validateFeeChallenge;
 import static google.registry.flows.domain.DomainFlowUtils.verifyUnitIsYears;
 import static google.registry.model.domain.DomainResource.MAX_REGISTRATION_YEARS;
 import static google.registry.model.domain.DomainResource.extendRegistrationWithCap;
-import static google.registry.model.domain.fee.Fee.FEE_RENEW_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.util.DateTimeUtils.leapSafeAddYears;
 
@@ -53,7 +52,7 @@ import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.fee.BaseFee.FeeType;
 import google.registry.model.domain.fee.Fee;
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import google.registry.model.domain.fee.FeeRenewCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import google.registry.model.domain.metadata.MetadataExtension;
 import google.registry.model.domain.rgp.GracePeriodStatus;
@@ -117,8 +116,7 @@ public final class DomainRenewFlow implements TransactionalFlow {
 
   @Override
   public final EppResponse run() throws EppException {
-    extensionManager.register(MetadataExtension.class);
+    extensionManager.register(FeeRenewCommandExtension.class, MetadataExtension.class);
-    extensionManager.registerAsGroup(FEE_RENEW_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     DateTime now = ofy().getTransactionTime();
@@ -127,8 +125,8 @@ public final class DomainRenewFlow implements TransactionalFlow {
     DomainResource existingDomain = loadAndVerifyExistence(DomainResource.class, targetId, now);
     verifyRenewAllowed(authInfo, existingDomain, command);
     int years = command.getPeriod().getValue();
-    FeeTransformCommandExtension feeRenew =
+    FeeRenewCommandExtension feeRenew =
-        eppInput.getFirstExtensionOfClasses(FEE_RENEW_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeRenewCommandExtension.class);
     EppCommandOperations commandOperations = TldSpecificLogicProxy.getRenewPrice(
         Registry.get(existingDomain.getTld()), targetId, clientId, now, years, eppInput);
     validateFeeChallenge(
@@ -217,7 +215,7 @@ public final class DomainRenewFlow implements TransactionalFlow {
   }
 
   private ImmutableList<FeeTransformResponseExtension> createResponseExtensions(
-      Money renewCost, FeeTransformCommandExtension feeRenew) {
+      Money renewCost, FeeRenewCommandExtension feeRenew) {
     return (feeRenew == null) ? null : ImmutableList.of(feeRenew
         .createResponseBuilder()
         .setCurrency(renewCost.getCurrencyUnit())

java/google/registry/flows/domain/DomainRestoreRequestFlow.java

@@ -25,7 +25,6 @@ import static google.registry.flows.domain.DomainFlowUtils.newAutorenewPollMessa
 import static google.registry.flows.domain.DomainFlowUtils.validateFeeChallenge;
 import static google.registry.flows.domain.DomainFlowUtils.verifyNotReserved;
 import static google.registry.flows.domain.DomainFlowUtils.verifyPremiumNameIsNotBlocked;
-import static google.registry.model.domain.fee.Fee.FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.util.DateTimeUtils.END_OF_TIME;
 
@@ -53,8 +52,8 @@ import google.registry.model.domain.DomainCommand.Update;
 import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.fee.BaseFee.FeeType;
 import google.registry.model.domain.fee.Fee;
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import google.registry.model.domain.fee.FeeUpdateCommandExtension;
 import google.registry.model.domain.metadata.MetadataExtension;
 import google.registry.model.domain.rgp.GracePeriodStatus;
 import google.registry.model.domain.rgp.RgpUpdateExtension;
@@ -119,8 +118,10 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
 
   @Override
   public final EppResponse run() throws EppException {
-    extensionManager.register(MetadataExtension.class, RgpUpdateExtension.class);
+    extensionManager.register(
-    extensionManager.registerAsGroup(FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        FeeUpdateCommandExtension.class,
+        MetadataExtension.class,
+        RgpUpdateExtension.class);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     Update command = (Update) resourceCommand;
@@ -129,8 +130,8 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
     Money restoreCost = Registry.get(existingDomain.getTld()).getStandardRestoreCost();
     EppCommandOperations renewCommandOperations = TldSpecificLogicProxy.getRenewPrice(
         Registry.get(existingDomain.getTld()), targetId, clientId, now, 1, eppInput);
-    FeeTransformCommandExtension feeUpdate = eppInput.getFirstExtensionOfClasses(
+    FeeUpdateCommandExtension feeUpdate =
-        FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeUpdateCommandExtension.class);
     Money totalCost = renewCommandOperations.getTotalCost();
     verifyRestoreAllowed(command, existingDomain, restoreCost, totalCost, feeUpdate, now);
     HistoryEntry historyEntry = buildHistory(existingDomain, now);
@@ -184,7 +185,7 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
       DomainResource existingDomain,
       Money restoreCost,
       Money renewCost,
-      FeeTransformCommandExtension feeUpdate,
+      FeeUpdateCommandExtension feeUpdate,
       DateTime now) throws EppException {
     verifyOptionalAuthInfo(authInfo, existingDomain);
     if (!isSuperuser) {
@@ -258,7 +259,7 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
   }
 
   private static ImmutableList<FeeTransformResponseExtension> createResponseExtensions(
-      Money restoreCost, Money renewCost, FeeTransformCommandExtension feeUpdate) {
+      Money restoreCost, Money renewCost, FeeUpdateCommandExtension feeUpdate) {
     return (feeUpdate == null) ? null : ImmutableList.of(
         feeUpdate.createResponseBuilder()
             .setCurrency(restoreCost.getCurrencyUnit())

java/google/registry/flows/domain/DomainTransferRequestFlow.java

@@ -30,7 +30,6 @@ import static google.registry.flows.domain.DomainFlowUtils.validateFeeChallenge;
 import static google.registry.flows.domain.DomainFlowUtils.verifyPremiumNameIsNotBlocked;
 import static google.registry.flows.domain.DomainFlowUtils.verifyUnitIsYears;
 import static google.registry.model.domain.DomainResource.extendRegistrationWithCap;
-import static google.registry.model.domain.fee.Fee.FEE_TRANSFER_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.eppoutput.Result.Code.SUCCESS_WITH_ACTION_PENDING;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.pricing.PricingEngineProxy.getDomainRenewCost;
@@ -56,7 +55,7 @@ import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.fee.BaseFee.FeeType;
 import google.registry.model.domain.fee.Fee;
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import google.registry.model.domain.fee.FeeTransferCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import google.registry.model.domain.flags.FlagsTransferCommandExtension;
 import google.registry.model.domain.metadata.MetadataExtension;
@@ -130,8 +129,10 @@ public final class DomainTransferRequestFlow implements TransactionalFlow {
 
   @Override
   public final EppResponse run() throws EppException {
-    extensionManager.register(FlagsTransferCommandExtension.class, MetadataExtension.class);
+    extensionManager.register(
-    extensionManager.registerAsGroup(FEE_TRANSFER_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        FeeTransferCommandExtension.class,
+        FlagsTransferCommandExtension.class,
+        MetadataExtension.class);
     extensionManager.validate();
     validateClientIsLoggedIn(gainingClientId);
     Period period = ((Transfer) resourceCommand).getPeriod();
@@ -144,8 +145,8 @@ public final class DomainTransferRequestFlow implements TransactionalFlow {
     // The cost of the renewal implied by a transfer.
     Money renewCost = getDomainRenewCost(targetId, now, years);
     // An optional extension from the client specifying what they think the transfer should cost.
-    FeeTransformCommandExtension feeTransfer = eppInput.getFirstExtensionOfClasses(
+    FeeTransferCommandExtension feeTransfer =
-        FEE_TRANSFER_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeTransferCommandExtension.class);
     validateFeeChallenge(targetId, tld, now, feeTransfer, renewCost);
     HistoryEntry historyEntry = buildHistory(period, existingDomain, now);
     DateTime automaticTransferTime = now.plus(registry.getAutomaticTransferLength());
@@ -405,7 +406,7 @@ public final class DomainTransferRequestFlow implements TransactionalFlow {
   }
 
   private ImmutableList<FeeTransformResponseExtension> createResponseExtensions(Money renewCost,
-      FeeTransformCommandExtension feeTransfer) {
+      FeeTransferCommandExtension feeTransfer) {
     return feeTransfer == null
         ? null
         : ImmutableList.of(feeTransfer.createResponseBuilder()

java/google/registry/flows/domain/DomainUpdateFlow.java

@@ -37,7 +37,6 @@ import static google.registry.flows.domain.DomainFlowUtils.validateRegistrantAll
 import static google.registry.flows.domain.DomainFlowUtils.validateRequiredContactsPresent;
 import static google.registry.flows.domain.DomainFlowUtils.verifyClientUpdateNotProhibited;
 import static google.registry.flows.domain.DomainFlowUtils.verifyNotInPendingDelete;
-import static google.registry.model.domain.fee.Fee.FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.util.DateTimeUtils.earliestOf;
 
@@ -63,6 +62,7 @@ import google.registry.model.domain.DomainCommand.Update.Change;
 import google.registry.model.domain.DomainResource;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import google.registry.model.domain.fee.FeeUpdateCommandExtension;
 import google.registry.model.domain.flags.FlagsUpdateCommandExtension;
 import google.registry.model.domain.metadata.MetadataExtension;
 import google.registry.model.domain.rgp.GracePeriodStatus;
@@ -147,10 +147,10 @@ public final class DomainUpdateFlow implements TransactionalFlow {
   @Override
   public EppResponse run() throws EppException {
     extensionManager.register(
+        FeeUpdateCommandExtension.class,
         FlagsUpdateCommandExtension.class,
         MetadataExtension.class,
         SecDnsUpdateExtension.class);
-    extensionManager.registerAsGroup(FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
     extensionManager.validate();
     validateClientIsLoggedIn(clientId);
     DateTime now = ofy().getTransactionTime();
@@ -201,7 +201,7 @@ public final class DomainUpdateFlow implements TransactionalFlow {
         Registry.get(tld), targetId, clientId, now, eppInput);
 
     FeeTransformCommandExtension feeUpdate =
-        eppInput.getFirstExtensionOfClasses(FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER);
+        eppInput.getSingleExtension(FeeUpdateCommandExtension.class);
     // If the fee extension is present, validate it (even if the cost is zero, to check for price
     // mismatches). Don't rely on the the validateFeeChallenge check for feeUpdate nullness, because
     // it throws an error if the name is premium, and we don't want to do that here.

java/google/registry/model/domain/fee/Fee.java

@@ -17,24 +17,8 @@ package google.registry.model.domain.fee;
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Range;
-import google.registry.model.domain.fee06.FeeCheckCommandExtensionV06;
-import google.registry.model.domain.fee06.FeeCreateCommandExtensionV06;
-import google.registry.model.domain.fee06.FeeRenewCommandExtensionV06;
-import google.registry.model.domain.fee06.FeeTransferCommandExtensionV06;
-import google.registry.model.domain.fee06.FeeUpdateCommandExtensionV06;
-import google.registry.model.domain.fee11.FeeCheckCommandExtensionV11;
-import google.registry.model.domain.fee11.FeeCreateCommandExtensionV11;
-import google.registry.model.domain.fee11.FeeRenewCommandExtensionV11;
-import google.registry.model.domain.fee11.FeeTransferCommandExtensionV11;
-import google.registry.model.domain.fee11.FeeUpdateCommandExtensionV11;
-import google.registry.model.domain.fee12.FeeCheckCommandExtensionV12;
-import google.registry.model.domain.fee12.FeeCreateCommandExtensionV12;
-import google.registry.model.domain.fee12.FeeRenewCommandExtensionV12;
-import google.registry.model.domain.fee12.FeeTransferCommandExtensionV12;
-import google.registry.model.domain.fee12.FeeUpdateCommandExtensionV12;
 import google.registry.model.eppcommon.ProtocolDefinition.ServiceExtension;
 import java.math.BigDecimal;
 import org.joda.time.DateTime;
@@ -60,49 +44,8 @@ public class Fee extends BaseFee {
     return instance;
   }
 
-  public static final ImmutableList<
+  public static final ImmutableSet<String> FEE_EXTENSION_URIS = ImmutableSet.of(
-          Class<? extends FeeCheckCommandExtension<
+      ServiceExtension.FEE_0_12.getUri(),
-              ? extends FeeCheckCommandExtensionItem, ? extends FeeCheckResponseExtension<?>>>>
+      ServiceExtension.FEE_0_11.getUri(),
-      FEE_CHECK_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER =
+      ServiceExtension.FEE_0_6.getUri());
-          ImmutableList.<
-                  Class<? extends FeeCheckCommandExtension<
-                      ? extends FeeCheckCommandExtensionItem,
-                      ? extends FeeCheckResponseExtension<?>>>>of(
-              FeeCheckCommandExtensionV12.class,
-              FeeCheckCommandExtensionV11.class,
-              FeeCheckCommandExtensionV06.class);
-
-  public static final ImmutableList<Class<? extends FeeTransformCommandExtension>>
-      FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER =
-          ImmutableList.<Class<? extends FeeTransformCommandExtension>>of(
-              FeeCreateCommandExtensionV12.class,
-              FeeCreateCommandExtensionV11.class,
-              FeeCreateCommandExtensionV06.class);
-
-  public static final ImmutableList<Class<? extends FeeTransformCommandExtension>>
-      FEE_RENEW_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER =
-          ImmutableList.<Class<? extends FeeTransformCommandExtension>>of(
-              FeeRenewCommandExtensionV12.class,
-              FeeRenewCommandExtensionV11.class,
-              FeeRenewCommandExtensionV06.class);
-
-  public static final ImmutableList<Class<? extends FeeTransformCommandExtension>>
-      FEE_TRANSFER_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER =
-          ImmutableList.<Class<? extends FeeTransformCommandExtension>>of(
-              FeeTransferCommandExtensionV12.class,
-              FeeTransferCommandExtensionV11.class,
-              FeeTransferCommandExtensionV06.class);
-
-  public static final ImmutableList<Class<? extends FeeTransformCommandExtension>>
-      FEE_UPDATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER =
-          ImmutableList.<Class<? extends FeeTransformCommandExtension>>of(
-              FeeUpdateCommandExtensionV12.class,
-              FeeUpdateCommandExtensionV11.class,
-              FeeUpdateCommandExtensionV06.class);
-
-  public static final ImmutableSet<String> FEE_EXTENSION_URIS =
-      ImmutableSet.<String>of(
-          ServiceExtension.FEE_0_12.getUri(),
-          ServiceExtension.FEE_0_11.getUri(),
-          ServiceExtension.FEE_0_6.getUri());
 }

java/google/registry/model/domain/fee/FeeCheckCommandExtensionItem.java

@@ -14,19 +14,22 @@
 
 package google.registry.model.domain.fee;
 
+import javax.xml.bind.annotation.XmlTransient;
+
 /**
  * Interface for individual fee extension items in Check commands. These are derived from the more
  * general query items (which cover Info commands as well), but may also contain a domain name,
  * depending on the version of the fee extension.
  */
-public interface FeeCheckCommandExtensionItem extends FeeQueryCommandExtensionItem {
+@XmlTransient
+public abstract class FeeCheckCommandExtensionItem extends FeeQueryCommandExtensionItem {
 
   /** True if this version of the fee extension supports domain names in Check items. */
-  public boolean isDomainNameSupported();
+  public abstract boolean isDomainNameSupported();
 
   /** The domain name being checked; throws an exception if domain names are not supported. */
-  public String getDomainName() throws UnsupportedOperationException;
+  public abstract String getDomainName();
 
   /** Create a builder for a matching fee check response item. */
-  public FeeCheckResponseExtensionItem.Builder createResponseBuilder();
+  public abstract FeeCheckResponseExtensionItem.Builder<?> createResponseBuilder();
 }

java/google/registry/model/domain/fee/FeeCheckResponseExtensionItem.java

@@ -14,20 +14,24 @@
 
 package google.registry.model.domain.fee;
 
-/**
+import javax.xml.bind.annotation.XmlTransient;
- * Interface for individual fee extension items in Check responses. These are derived from the more
- * general query items (which cover Info responses as well), but may also contain a domain name,
- * depending on the version of the fee extension.
- */
-public interface FeeCheckResponseExtensionItem extends FeeQueryResponseExtensionItem {
 
-  /** Builder for {@link FeeCheckResponseExtensionItem}. */
+/**
-  public interface Builder extends FeeQueryResponseExtensionItem.Builder {
+ * Abstract class for individual fee extension items in Check responses. These are derived from the
+ * more general query items (which cover Info responses as well), but may also contain a domain
+ * name, depending on the version of the fee extension.
+ */
+@XmlTransient
+public abstract class FeeCheckResponseExtensionItem extends FeeQueryResponseExtensionItem {
+
+  /** Abstract builder for {@link FeeCheckResponseExtensionItem}. */
+  public abstract static class Builder<T extends FeeCheckResponseExtensionItem>
+      extends FeeQueryResponseExtensionItem.Builder<T, Builder<T>> {
 
     /** The name associated with the item. Has no effect if domain names are not supported. */
-    public Builder setDomainNameIfSupported(String name);
+    public Builder<T> setDomainNameIfSupported(@SuppressWarnings("unused") String name) {
-
+      return this;  // Default impl is a noop.
-    public FeeCheckResponseExtensionItem build();
+    }
   }
 }
 

java/google/registry/model/domain/fee/FeeCreateCommandExtension.java

@@ -0,0 +1,21 @@
+// Copyright 2016 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.model.domain.fee;
+
+import javax.xml.bind.annotation.XmlTransient;
+
+/** A fee extension that may be present on domain create commands. */
+@XmlTransient
+public abstract class FeeCreateCommandExtension extends FeeTransformCommandExtension {}

java/google/registry/model/domain/fee/FeeQueryCommandExtensionItem.java

@@ -15,17 +15,20 @@
 package google.registry.model.domain.fee;
 
 import com.google.common.base.Optional;
+import google.registry.model.ImmutableObject;
 import google.registry.model.domain.Period;
+import javax.xml.bind.annotation.XmlTransient;
 import org.joda.money.CurrencyUnit;
 import org.joda.time.DateTime;
 
 /**
- * Interface for individual query items in Check and Info commands. Each item indicates the command
+ * Abstract base class for the fee request query items used in Check and Info commands. It handles
- * to be checked, and the number of years for which the prices is requested. It may also contain the
+ * the period, which is always present. Derived classes must handle the command, which may be
- * currency, but some versions of the fee extension specify the currency at the top level of the
+ * implemented in different ways, and the currency, which may or may not be present, depending on
- * extension.
+ * the version of the extension being used.
  */
-public interface FeeQueryCommandExtensionItem {
+@XmlTransient
+public abstract class FeeQueryCommandExtensionItem extends ImmutableObject {
 
   /** The name of a command that might have an associated fee. */
   public enum CommandName {
@@ -37,28 +40,35 @@ public interface FeeQueryCommandExtensionItem {
     UPDATE
   }
 
+  /** The default validity period (if not specified) is 1 year for all operations. */
+  static final Period DEFAULT_PERIOD = Period.create(1, Period.Unit.YEARS);
+
+  /** The period for the command being checked. */
+  Period period;
+
   /**
    * Three-character ISO4217 currency code.
    *
    * <p>Returns null if this version of the fee extension doesn't specify currency at the top level.
    */
-  public CurrencyUnit getCurrency();
+  public abstract CurrencyUnit getCurrency();
 
   /** The as-of date for the fee extension to run. */
-  public Optional<DateTime> getEffectiveDate();
+  public abstract Optional<DateTime> getEffectiveDate();
 
   /** The name of the command being checked. */
-  public CommandName getCommandName();
+  public abstract CommandName getCommandName();
 
-  /** The unparse name of the command being checked, for use in error strings. */
+  /** The command name before being parsed into an enum, for use in error strings. */
-  public String getUnparsedCommandName();
+  public abstract String getUnparsedCommandName();
 
   /** The phase of the command being checked. */
-  public String getPhase();
+  public abstract String getPhase();
 
   /** The subphase of the command being checked. */
-  public String getSubphase();
+  public abstract String getSubphase();
 
-  /** The period for the command being checked. */
+  public Period getPeriod() {
-  public Period getPeriod();
+    return Optional.fromNullable(period).or(DEFAULT_PERIOD);
+  }
 }

java/google/registry/model/domain/fee/FeeQueryCommandExtensionItemImpl.java

@@ -1,68 +0,0 @@
-// Copyright 2016 The Nomulus Authors. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package google.registry.model.domain.fee;
-
-import com.google.common.base.Optional;
-import google.registry.model.ImmutableObject;
-import google.registry.model.domain.Period;
-import javax.xml.bind.annotation.XmlTransient;
-
-/**
- * Abstract base class for the fee request query items used in Check and Info commands. It handles
- * command and period, which are always present. Derived classes must handle currency, which may or
- * may not be present, depending on the version of the extension being used.
- */
-@XmlTransient
-public abstract class FeeQueryCommandExtensionItemImpl
-    extends ImmutableObject implements FeeQueryCommandExtensionItem {
-
-  /** The default validity period (if not specified) is 1 year for all operations. */
-  static final Period DEFAULT_PERIOD = Period.create(1, Period.Unit.YEARS);
-
-  /** The command being checked. */
-  FeeExtensionCommandDescriptor command;
-
-  /** The period for the command being checked. */
-  Period period;
-
-  /** The name of the command being checked. */
-  @Override
-  public CommandName getCommandName() {
-    return command.getCommand();
-  }
-
-  /** The command name before being parsed into an enum, for use in error strings. */
-  @Override
-  public String getUnparsedCommandName() {
-    return command.getUnparsedCommandName();
-  }
-
-  /** The phase of the command being checked. */
-  @Override
-  public String getPhase() {
-    return command.getPhase();
-  }
-
-  /** The subphase of the command being checked. */
-  @Override
-  public String getSubphase() {
-    return command.getSubphase();
-  }
-
-  @Override
-  public Period getPeriod() {
-    return Optional.fromNullable(period).or(DEFAULT_PERIOD);
-  }
-}

java/google/registry/model/domain/fee/FeeQueryResponseExtensionItem.java

@@ -14,56 +14,112 @@
 
 package google.registry.model.domain.fee;
 
+import static google.registry.util.CollectionUtils.forceEmptyToNull;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.Buildable.GenericBuilder;
+import google.registry.model.ImmutableObject;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.fee.FeeQueryCommandExtensionItem.CommandName;
 import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
+import javax.xml.bind.annotation.XmlTransient;
 import org.joda.money.CurrencyUnit;
 import org.joda.time.DateTime;
 
 /**
- * Interface for individual query items in Check and Info response. Each item indicates the fees and
+ * Abstract base class for the fee request query items used in Check and Info responses. It handles
- * class associated with a particular command and period. The currency may also be listed, but some
+ * command, period, fees and class, which are always present. Derived classes must handle currency,
- * versions of the fee extension specify the currency at the top level of the extension.
+ * which may or may not be present, depending on the version of the extension being used.
  */
-
+@XmlTransient
-public interface FeeQueryResponseExtensionItem {
+public class FeeQueryResponseExtensionItem extends ImmutableObject {
 
   /**
-   * The type of the fee. We will use "premium" for fees on premium names, and omit the field
+   * The period that was checked.
-   * otherwise.
+   *
+   * <p>This field is exposed to JAXB only via the getter so that subclasses can override it.
    */
-  public String getFeeClass();
+  @XmlTransient
+  Period period;
 
-  /** Builder for {@link FeeCheckResponseExtensionItem}. */
+  /**
-  public interface Builder {
+   * The magnitude of the fee, in the specified units, with an optional description.
+   *
+   * <p>This is a list because a single operation can involve multiple fees.
+   *
+   * <p>This field is exposed to JAXB only via the getter so that subclasses can override it.
+   */
+  @XmlTransient
+  List<Fee> fees;
 
-    /**
+  /**
-     * If currency is not supported in this type of query response item for this version of the fee
+   * The type of the fee.
-     * extension, this function has no effect.
+   *
-     */
+   * <p>We will use "premium" for fees on premium names, and omit the field otherwise.
-    public Builder setCurrencyIfSupported(CurrencyUnit currency);
+   *
+   * <p>This field is exposed to JAXB only via the getter so that subclasses can override it.
+   */
+  @XmlTransient
+  String feeClass;
 
-     /** Whether this check item can be calculated. If so, reason should be null. If not, fees
+  @XmlElement(name = "period")
-      * should not be set.
+  public Period getPeriod() {
-      */
+    return period;
-    public Builder setAvailIfSupported(boolean avail);
+  }
 
-    /** The reason that the check item cannot be calculated. */
+  @XmlElement(name = "fee")
-    public Builder setReasonIfSupported(String reason);
+  public ImmutableList<Fee> getFees() {
+    return nullToEmptyImmutableCopy(fees);
+  }
 
-    /** The effective date that the check is run on. */
+  @XmlElement(name = "class")
-    public Builder setEffectiveDateIfSupported(DateTime effectiveDate);
+  public String getFeeClass() {
+    return feeClass;
+  }
 
-    /** The date after which the quoted fees are no longer valid. */
+  /** Abstract builder for {@link FeeQueryResponseExtensionItemImpl}. */
-    public Builder setNotAfterDateIfSupported(DateTime notAfterDate);
+  public abstract static class
+      Builder<T extends FeeQueryResponseExtensionItem, B extends Builder<?, ?>>
+          extends GenericBuilder<T, B> {
 
-    public Builder setCommand(CommandName commandName, String phase, String subphase);
+    public abstract B setCommand(CommandName commandName, String phase, String subphase);
 
-    public Builder setPeriod(Period period);
+    public B setPeriod(Period period) {
+      getInstance().period = period;
+      return thisCastToDerived();
+    }
 
-    public Builder setFees(List<Fee> fees);
+    public B setFees(ImmutableList<Fee> fees) {
+      // If there are no fees, set the field to null to suppress the 'fee' section in the xml.
+      getInstance().fees = forceEmptyToNull(ImmutableList.copyOf(fees));
+      return thisCastToDerived();
+    }
 
-    public Builder setClass(String feeClass);
+    public B setClass(String feeClass) {
+      getInstance().feeClass = feeClass;
+      return thisCastToDerived();
+    }
+
+    public B setAvailIfSupported(@SuppressWarnings("unused") boolean avail) {
+      return thisCastToDerived();  // Default impl is a noop.
+    }
+
+    public B setReasonIfSupported(@SuppressWarnings("unused") String reason) {
+      return thisCastToDerived();  // Default impl is a noop.
+    }
+
+    public B setEffectiveDateIfSupported(@SuppressWarnings("unused") DateTime effectiveDate) {
+      return thisCastToDerived();  // Default impl is a noop.
+    }
+
+    public B setNotAfterDateIfSupported(@SuppressWarnings("unused") DateTime notAfterDate) {
+      return thisCastToDerived();  // Default impl is a noop.
+    }
+
+    public B setCurrencyIfSupported(@SuppressWarnings("unused") CurrencyUnit currency) {
+      return thisCastToDerived();  // Default impl is a noop.
+    }
   }
 }
-

java/google/registry/model/domain/fee/FeeQueryResponseExtensionItemImpl.java

@@ -1,98 +0,0 @@
-// Copyright 2016 The Nomulus Authors. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package google.registry.model.domain.fee;
-
-import static google.registry.util.CollectionUtils.forceEmptyToNull;
-
-import com.google.common.collect.ImmutableList;
-import google.registry.model.Buildable.GenericBuilder;
-import google.registry.model.ImmutableObject;
-import google.registry.model.domain.Period;
-import google.registry.model.domain.fee.FeeQueryCommandExtensionItem.CommandName;
-import java.util.List;
-import javax.xml.bind.annotation.XmlElement;
-import javax.xml.bind.annotation.XmlTransient;
-
-/**
- * Abstract base class for the fee request query items used in Check and Info responses. It handles
- * command, period, fees and class, which are always present. Derived classes must handle currency,
- * which may or may not be present, depending on the version of the extension being used.
- */
-@XmlTransient
-public class FeeQueryResponseExtensionItemImpl
-    extends ImmutableObject implements FeeQueryResponseExtensionItem {
-
-  /** The command that was checked. */
-  FeeExtensionCommandDescriptor command;
-
-  /** The period that was checked. */
-  Period period;
-
-  /**
-   * The magnitude of the fee, in the specified units, with an optional description.
-   *
-   * <p>This is a list because a single operation can involve multiple fees.
-   */
-  List<Fee> fee;
-
-  /**
-   * The type of the fee.
-   *
-   * <p>We will use "premium" for fees on premium names, and omit the field otherwise.
-   */
-  @XmlElement(name = "class")
-  String feeClass;
-
-  @Override
-  public String getFeeClass() {
-    return feeClass;
-  }
-
-  /** Abstract builder for {@link FeeQueryResponseExtensionItemImpl}. */
-  public abstract static class
-      Builder<T extends FeeQueryResponseExtensionItemImpl, B extends Builder<?, ?>>
-          extends GenericBuilder<T, B> implements FeeQueryResponseExtensionItem.Builder {
-
-    @Override
-    public B setCommand(CommandName commandName, String phase, String subphase) {
-      getInstance().command = FeeExtensionCommandDescriptor.create(commandName, phase, subphase);
-      return thisCastToDerived();
-    }
-
-    @Override
-    public B setPeriod(Period period) {
-      getInstance().period = period;
-      return thisCastToDerived();
-    }
-
-    @Override
-    public B setFees(List<Fee> fees) {
-      // If there are no fees, set the field to null to suppress the 'fee' section in the xml.
-      getInstance().fee = forceEmptyToNull(ImmutableList.copyOf(fees));
-      return thisCastToDerived();
-    }
-
-    public B setFee(List<Fee> fees) {
-      getInstance().fee = forceEmptyToNull(ImmutableList.copyOf(fees));
-      return thisCastToDerived();
-    }
-
-    @Override
-    public B setClass(String feeClass) {
-      getInstance().feeClass = feeClass;
-      return thisCastToDerived();
-    }
-  }
-}

java/google/registry/model/domain/fee/FeeRenewCommandExtension.java

@@ -0,0 +1,21 @@
+// Copyright 2016 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.model.domain.fee;
+
+import javax.xml.bind.annotation.XmlTransient;
+
+/** A fee extension that may be present on domain renew commands. */
+@XmlTransient
+public abstract class FeeRenewCommandExtension extends FeeTransformCommandExtension {}

java/google/registry/model/domain/fee/FeeTransferCommandExtension.java

@@ -0,0 +1,21 @@
+// Copyright 2016 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.model.domain.fee;
+
+import javax.xml.bind.annotation.XmlTransient;
+
+/** A fee extension that may be present on domain transfer commands. */
+@XmlTransient
+public abstract class FeeTransferCommandExtension  extends FeeTransformCommandExtension {}

java/google/registry/model/domain/fee/FeeTransformCommandExtension.java

@@ -14,14 +14,41 @@
 
 package google.registry.model.domain.fee;
 
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.ImmutableObject;
 import google.registry.model.eppinput.EppInput.CommandExtension;
 import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
+import javax.xml.bind.annotation.XmlTransient;
 import org.joda.money.CurrencyUnit;
 
-/** Interface for fee extensions in Create, Renew, Transfer and Update commands. */
+/** Base class for general transform commands with fees (create, renew, update, transfer). */
-public interface FeeTransformCommandExtension extends CommandExtension {
+@XmlTransient
-  CurrencyUnit getCurrency();
+public abstract class FeeTransformCommandExtension
-  List<Fee> getFees();
+    extends ImmutableObject implements CommandExtension {
-  List<Credit> getCredits();
+
-  FeeTransformResponseExtension.Builder createResponseBuilder();
+  /** The currency of the fee. */
+  CurrencyUnit currency;
+
+  /**
+   * The magnitude of the fee, in the specified units, with an optional description.
+   *
+   * <p>This is a list because a single operation can involve multiple fees.
+   */
+  @XmlElement(name = "fee")
+  List<Fee> fees;
+
+  public CurrencyUnit getCurrency() {
+    return currency;
+  }
+
+  public ImmutableList<Fee> getFees() {
+    return nullToEmptyImmutableCopy(fees);
+  }
+
+  public abstract ImmutableList<Credit> getCredits();
+
+  public abstract FeeTransformResponseExtension.Builder createResponseBuilder();
 }

java/google/registry/model/domain/fee/FeeTransformCommandExtensionImpl.java

@@ -1,58 +0,0 @@
-// Copyright 2016 The Nomulus Authors. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package google.registry.model.domain.fee;
-
-import static google.registry.util.CollectionUtils.nullToEmpty;
-
-import google.registry.model.ImmutableObject;
-import java.util.List;
-import javax.xml.bind.annotation.XmlElement;
-import javax.xml.bind.annotation.XmlTransient;
-import org.joda.money.CurrencyUnit;
-
-/** Base class for general transform commands with fees (create, renew, update, transfer). */
-@XmlTransient
-public abstract class FeeTransformCommandExtensionImpl
-    extends ImmutableObject implements FeeTransformCommandExtension {
-
-  /** The currency of the fee. */
-  CurrencyUnit currency;
-
-  /**
-   * The magnitude of the fee, in the specified units, with an optional description.
-   *
-   * <p>This is a list because a single operation can involve multiple fees.
-   */
-  @XmlElement(name = "fee")
-  List<Fee> fees;
-
-  @XmlElement(name = "credit")
-  List<Credit> credits;
-
-  @Override
-  public CurrencyUnit getCurrency() {
-    return currency;
-  }
-
-  @Override
-  public List<Fee> getFees() {
-    return fees;
-  }
-
-  @Override
-  public List<Credit> getCredits() {
-    return nullToEmpty(credits);
-  }
-}

java/google/registry/model/domain/fee/FeeTransformCommandExtensionImplNoCredits.java

@@ -1,58 +0,0 @@
-// Copyright 2016 The Nomulus Authors. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package google.registry.model.domain.fee;
-
-import com.google.common.collect.ImmutableList;
-import google.registry.model.ImmutableObject;
-import java.util.List;
-import javax.xml.bind.annotation.XmlElement;
-import javax.xml.bind.annotation.XmlTransient;
-import org.joda.money.CurrencyUnit;
-
-/**
- * Base class for general transform commands with fees (create, renew, update, transfer). This
- * version of the class is for fee extensions that do not support credits (certain older versions
- * allow credits only for some commands).
- */
-@XmlTransient
-public abstract class FeeTransformCommandExtensionImplNoCredits
-    extends ImmutableObject implements FeeTransformCommandExtension {
-
-  /** The currency of the fee. */
-  CurrencyUnit currency;
-
-  /**
-   * The magnitude of the fee, in the specified units, with an optional description.
-   *
-   * <p>This is a list because a single operation can involve multiple fees.
-   */
-  @XmlElement(name = "fee")
-  List<Fee> fees;
-
-  @Override
-  public CurrencyUnit getCurrency() {
-    return currency;
-  }
-
-  @Override
-  public List<Fee> getFees() {
-    return fees;
-  }
-
-  @Override
-  public List<Credit> getCredits() {
-    return ImmutableList.of();
-  }
-}

java/google/registry/model/domain/fee/FeeTransformResponseExtension.java

@@ -14,18 +14,62 @@
 
 package google.registry.model.domain.fee;
 
+import static google.registry.util.CollectionUtils.forceEmptyToNull;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.Buildable;
+import google.registry.model.ImmutableObject;
 import google.registry.model.eppoutput.EppResponse.ResponseExtension;
 import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
+import javax.xml.bind.annotation.XmlTransient;
 import org.joda.money.CurrencyUnit;
 
-/** Interface for fee extensions in Create, Renew, Transfer and Update responses. */
+/** Base class for fee responses on general transform commands (create, update, renew, transfer). */
-public interface FeeTransformResponseExtension extends ResponseExtension {
+@XmlTransient
+public class FeeTransformResponseExtension extends ImmutableObject implements ResponseExtension {
 
-  /** Builder for {@link FeeTransformResponseExtension}. */
+  /** The currency of the fee. */
-  public interface Builder {
+  CurrencyUnit currency;
-    Builder setCurrency(CurrencyUnit currency);
+
-    Builder setFees(List<Fee> fees);
+  /**
-    Builder setCredits(List<Credit> credits);
+   * The magnitude of the fee, in the specified units, with an optional description.
-    FeeTransformResponseExtension build();
+   *
+   * <p>This is a list because a single operation can involve multiple fees.
+   */
+  @XmlElement(name = "fee")
+  List<Fee> fees;
+
+  /** This field is exposed to JAXB only via the getter so that subclasses can override it. */
+  @XmlTransient
+  List<Credit> credits;
+
+  @XmlElement(name = "credit")
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
+
+  /** Abstract builder for {@link FeeTransformResponseExtensionImpl}. */
+  public static class Builder extends Buildable.Builder<FeeTransformResponseExtension> {
+
+    public Builder(FeeTransformResponseExtension instance) {
+      super(instance);
+    }
+
+    public Builder setCurrency(CurrencyUnit currency) {
+      getInstance().currency = currency;
+      return this;
+    }
+
+    public Builder setFees(List<Fee> fees) {
+      getInstance().fees = fees;
+      return this;
+    }
+
+    public Builder setCredits(List<Credit> credits) {
+      getInstance().credits = forceEmptyToNull(credits);
+      return this;
+    }
   }
 }

java/google/registry/model/domain/fee/FeeTransformResponseExtensionImpl.java

@@ -1,68 +0,0 @@
-// Copyright 2016 The Nomulus Authors. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package google.registry.model.domain.fee;
-
-import static google.registry.util.CollectionUtils.forceEmptyToNull;
-
-import google.registry.model.Buildable.GenericBuilder;
-import google.registry.model.ImmutableObject;
-import java.util.List;
-import javax.xml.bind.annotation.XmlElement;
-import javax.xml.bind.annotation.XmlTransient;
-import org.joda.money.CurrencyUnit;
-
-/** Base class for fee responses on general transform commands (create, update, renew, transfer). */
-@XmlTransient
-public class FeeTransformResponseExtensionImpl extends ImmutableObject
-    implements FeeTransformResponseExtension {
-
-  /** The currency of the fee. */
-  CurrencyUnit currency;
-
-  /**
-   * The magnitude of the fee, in the specified units, with an optional description.
-   *
-   * <p>This is a list because a single operation can involve multiple fees.
-   */
-  @XmlElement(name = "fee")
-  List<Fee> fees;
-
-  @XmlElement(name = "credit")
-  List<Credit> credits;
-
-  /** Abstract builder for {@link FeeTransformResponseExtensionImpl}. */
-  public abstract static class
-      Builder<T extends FeeTransformResponseExtensionImpl, B extends Builder<?, ?>>
-          extends GenericBuilder<T, B> implements FeeTransformResponseExtension.Builder {
-
-    @Override
-    public B setCurrency(CurrencyUnit currency) {
-      getInstance().currency = currency;
-      return thisCastToDerived();
-    }
-
-    @Override
-    public B setFees(List<Fee> fees) {
-      getInstance().fees = fees;
-      return thisCastToDerived();
-    }
-
-    @Override
-    public B setCredits(List<Credit> credits) {
-      getInstance().credits = forceEmptyToNull(credits);
-      return thisCastToDerived();
-    }
-  }
-}

java/google/registry/model/domain/fee/FeeTransformResponseExtensionImplNoCredits.java

@@ -1,66 +0,0 @@
-// Copyright 2016 The Nomulus Authors. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package google.registry.model.domain.fee;
-
-import google.registry.model.Buildable.GenericBuilder;
-import google.registry.model.ImmutableObject;
-import java.util.List;
-import javax.xml.bind.annotation.XmlElement;
-import javax.xml.bind.annotation.XmlTransient;
-import org.joda.money.CurrencyUnit;
-
-/**
- * Base class for fee responses on general transform commands (create, update, renew, transfer).
- * This version of the class is for fee extensions that do not support credits (certain older
- * versions allow credits only for some commands).
- */
-@XmlTransient
-public class FeeTransformResponseExtensionImplNoCredits extends ImmutableObject
-    implements FeeTransformResponseExtension {
-
-  /** The currency of the fee. */
-  CurrencyUnit currency;
-
-  /**
-   * The magnitude of the fee, in the specified units, with an optional description.
-   *
-   * <p>This is a list because a single operation can involve multiple fees.
-   */
-  @XmlElement(name = "fee")
-  List<Fee> fees;
-
-  /** Abstract builder for {@link FeeTransformResponseExtensionImplNoCredits}. */
-  public abstract static class
-      Builder<T extends FeeTransformResponseExtensionImplNoCredits, B extends Builder<?, ?>>
-          extends GenericBuilder<T, B> implements FeeTransformResponseExtension.Builder {
-
-    @Override
-    public B setCurrency(CurrencyUnit currency) {
-      getInstance().currency = currency;
-      return thisCastToDerived();
-    }
-
-    @Override
-    public B setFees(List<Fee> fees) {
-      getInstance().fees = fees;
-      return thisCastToDerived();
-    }
-
-    @Override
-    public B setCredits(List<Credit> credits) {
-      return thisCastToDerived();
-    }
-  }
-}

java/google/registry/model/domain/fee/FeeUpdateCommandExtension.java

@@ -0,0 +1,21 @@
+// Copyright 2016 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.model.domain.fee;
+
+import javax.xml.bind.annotation.XmlTransient;
+
+/** A fee extension that may be present on domain update commands. */
+@XmlTransient
+public abstract class FeeUpdateCommandExtension extends FeeTransformCommandExtension {}

java/google/registry/model/domain/fee06/FeeCheckCommandExtensionItemV06.java

@@ -16,22 +16,47 @@ package google.registry.model.domain.fee06;
 
 import com.google.common.base.Optional;
 import google.registry.model.domain.fee.FeeCheckCommandExtensionItem;
-import google.registry.model.domain.fee.FeeCheckResponseExtensionItem;
+import google.registry.model.domain.fee.FeeExtensionCommandDescriptor;
-import google.registry.model.domain.fee.FeeQueryCommandExtensionItemImpl;
 import javax.xml.bind.annotation.XmlType;
 import org.joda.money.CurrencyUnit;
 import org.joda.time.DateTime;
 
 /** An individual price check item in version 0.6 of the fee extension on Check commands. */
 @XmlType(propOrder = {"name", "currency", "command", "period"})
-public class FeeCheckCommandExtensionItemV06
+public class FeeCheckCommandExtensionItemV06 extends FeeCheckCommandExtensionItem {
-    extends FeeQueryCommandExtensionItemImpl implements FeeCheckCommandExtensionItem {
 
   /** The fully qualified domain name being checked. */
   String name;
 
   CurrencyUnit currency;
 
+  /** The command being checked.  */
+  FeeExtensionCommandDescriptor command;
+
+  /** The name of the command being checked. */
+  @Override
+  public CommandName getCommandName() {
+    return command.getCommand();
+  }
+
+  /** The command name before being parsed into an enum, for use in error strings. */
+  @Override
+  public String getUnparsedCommandName() {
+    return command.getUnparsedCommandName();
+  }
+
+  /** The phase of the command being checked. */
+  @Override
+  public String getPhase() {
+    return command.getPhase();
+  }
+
+  /** The subphase of the command being checked. */
+  @Override
+  public String getSubphase() {
+    return command.getSubphase();
+  }
+
   @Override
   public boolean isDomainNameSupported() {
     return true;
@@ -48,7 +73,7 @@ public class FeeCheckCommandExtensionItemV06
   }
 
   @Override
-  public FeeCheckResponseExtensionItem.Builder createResponseBuilder() {
+  public FeeCheckResponseExtensionItemV06.Builder createResponseBuilder() {
     return new FeeCheckResponseExtensionItemV06.Builder();
   }
 

java/google/registry/model/domain/fee06/FeeCheckResponseExtensionItemV06.java

@@ -15,24 +15,31 @@
 package google.registry.model.domain.fee06;
 
 import google.registry.model.domain.fee.FeeCheckResponseExtensionItem;
-import google.registry.model.domain.fee.FeeQueryResponseExtensionItemImpl;
+import google.registry.model.domain.fee.FeeExtensionCommandDescriptor;
+import google.registry.model.domain.fee.FeeQueryCommandExtensionItem.CommandName;
 import javax.xml.bind.annotation.XmlType;
 import org.joda.money.CurrencyUnit;
-import org.joda.time.DateTime;
 
 /** The version 0.6 response for a domain check on a single resource. */
-@XmlType(propOrder = {"name", "currency", "command", "period", "fee", "feeClass"})
+@XmlType(propOrder = {"name", "currency", "command", "period", "fees", "feeClass"})
-public class FeeCheckResponseExtensionItemV06
+public class FeeCheckResponseExtensionItemV06 extends FeeCheckResponseExtensionItem {
-    extends FeeQueryResponseExtensionItemImpl implements FeeCheckResponseExtensionItem {
   /** The name of the domain that was checked, with an attribute indicating if it is premium. */
   String name;
 
   CurrencyUnit currency;
 
+  /** The command that was checked. */
+  FeeExtensionCommandDescriptor command;
+
   /** Builder for {@link FeeCheckResponseExtensionItemV06}. */
   public static class Builder
-      extends FeeQueryResponseExtensionItemImpl.Builder<FeeCheckResponseExtensionItemV06, Builder>
+      extends FeeCheckResponseExtensionItem.Builder<FeeCheckResponseExtensionItemV06> {
-      implements FeeCheckResponseExtensionItem.Builder {
+
+    @Override
+    public Builder setCommand(CommandName commandName, String phase, String subphase) {
+      getInstance().command = FeeExtensionCommandDescriptor.create(commandName, phase, subphase);
+      return this;
+    }
 
     @Override
     public Builder setDomainNameIfSupported(String name) {
@@ -45,26 +52,5 @@ public class FeeCheckResponseExtensionItemV06
       getInstance().currency = currency;
       return this;
     }
-
-    @Override
-    public Builder setAvailIfSupported(boolean avail) {
-      return this;
-    }
-
-    @Override
-    public Builder setReasonIfSupported(String reason) {
-      return this;
-    }
-
-    @Override
-    public Builder setEffectiveDateIfSupported(DateTime effectiveDate) {
-      return this;
-    }
-
-    @Override
-    public Builder setNotAfterDateIfSupported(DateTime notAfterDate) {
-      return this;
-    }
-
   }
 }

java/google/registry/model/domain/fee06/FeeCreateCommandExtensionV06.java

@@ -14,8 +14,9 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import com.google.common.collect.ImmutableList;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImplNoCredits;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeCreateCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
@@ -23,11 +24,19 @@ import javax.xml.bind.annotation.XmlType;
 /** A fee extension that may be present on domain create commands. */
 @XmlRootElement(name = "create")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeCreateCommandExtensionV06
+public class FeeCreateCommandExtensionV06 extends FeeCreateCommandExtension {
-    extends FeeTransformCommandExtensionImplNoCredits implements FeeTransformCommandExtension {
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeCreateResponseExtensionV06.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeCreateResponseExtensionV06());
+  }
+
+  /**
+   * This method is overridden and not annotated for JAXB because this version of the extension
+   * doesn't support the "credit" field.
+   */
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return ImmutableList.of();
   }
 }

java/google/registry/model/domain/fee06/FeeCreateResponseExtensionV06.java

@@ -14,7 +14,9 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImplNoCredits;
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +26,11 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "creData")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeCreateResponseExtensionV06 extends FeeTransformResponseExtensionImplNoCredits {
+public class FeeCreateResponseExtensionV06 extends FeeTransformResponseExtension {
-  /** A builder for {@link FeeCreateResponseExtensionV06}. */
+
-  public static class Builder extends
+  /** This version of the extension doesn't support the "credit" field. */
-      FeeTransformResponseExtensionImplNoCredits.Builder<FeeCreateResponseExtensionV06, Builder> {}
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return ImmutableList.of();
+  }
 }

java/google/registry/model/domain/fee06/FeeDeleteResponseExtensionV06.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,9 +24,12 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "delData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeDeleteResponseExtensionV06 extends FeeTransformResponseExtensionImpl {
+public class FeeDeleteResponseExtensionV06 extends FeeTransformResponseExtension {
 
   /** Builder for {@link FeeDeleteResponseExtensionV06}. */
-  public static class Builder
+  public static class Builder extends FeeTransformResponseExtension.Builder {
-      extends FeeTransformResponseExtensionImpl.Builder<FeeDeleteResponseExtensionV06, Builder> {}
+    public Builder() {
+      super(new FeeDeleteResponseExtensionV06());
+    }
+  }
 }

java/google/registry/model/domain/fee06/FeeInfoCommandExtensionV06.java

@@ -15,7 +15,8 @@
 package google.registry.model.domain.fee06;
 
 import com.google.common.base.Optional;
-import google.registry.model.domain.fee.FeeQueryCommandExtensionItemImpl;
+import google.registry.model.domain.fee.FeeExtensionCommandDescriptor;
+import google.registry.model.domain.fee.FeeQueryCommandExtensionItem;
 import google.registry.model.eppinput.EppInput.CommandExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
@@ -26,11 +27,38 @@ import org.joda.time.DateTime;
 @XmlRootElement(name = "info")
 @XmlType(propOrder = {"currency", "command", "period"})
 public class FeeInfoCommandExtensionV06
-    extends FeeQueryCommandExtensionItemImpl implements CommandExtension {
+    extends FeeQueryCommandExtensionItem implements CommandExtension {
 
   /** A three-character ISO4217 currency code. */
   CurrencyUnit currency;
 
+  /** The command being checked.  */
+  FeeExtensionCommandDescriptor command;
+
+  /** The name of the command being checked. */
+  @Override
+  public CommandName getCommandName() {
+    return command.getCommand();
+  }
+
+  /** The command name before being parsed into an enum, for use in error strings. */
+  @Override
+  public String getUnparsedCommandName() {
+    return command.getUnparsedCommandName();
+  }
+
+  /** The phase of the command being checked. */
+  @Override
+  public String getPhase() {
+    return command.getPhase();
+  }
+
+  /** The subphase of the command being checked. */
+  @Override
+  public String getSubphase() {
+    return command.getSubphase();
+  }
+
   @Override
   public CurrencyUnit getCurrency() {
     return currency;

java/google/registry/model/domain/fee06/FeeInfoResponseExtensionV06.java

@@ -14,54 +14,43 @@
 
 package google.registry.model.domain.fee06;
 
+import google.registry.model.domain.fee.FeeExtensionCommandDescriptor;
+import google.registry.model.domain.fee.FeeQueryCommandExtensionItem.CommandName;
 import google.registry.model.domain.fee.FeeQueryResponseExtensionItem;
-import google.registry.model.domain.fee.FeeQueryResponseExtensionItemImpl;
 import google.registry.model.eppoutput.EppResponse.ResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 import org.joda.money.CurrencyUnit;
-import org.joda.time.DateTime;
 
 /**
  * An XML data object that represents a fee extension that may be present on the response to EPP
  * domain info commands.
  */
 @XmlRootElement(name = "infData")
-@XmlType(propOrder = {"currency", "command", "period", "fee", "feeClass"})
+@XmlType(propOrder = {"currency", "command", "period", "fees", "feeClass"})
 public class FeeInfoResponseExtensionV06
-    extends FeeQueryResponseExtensionItemImpl implements ResponseExtension {
+    extends FeeQueryResponseExtensionItem implements ResponseExtension {
 
   CurrencyUnit currency;
 
+  /** The command that was checked. */
+  FeeExtensionCommandDescriptor command;
+
+
   /** Builder for {@link FeeInfoResponseExtensionV06}. */
   public static class Builder
-      extends FeeQueryResponseExtensionItemImpl.Builder<FeeInfoResponseExtensionV06, Builder> {
+      extends FeeQueryResponseExtensionItem.Builder<FeeInfoResponseExtensionV06, Builder> {
 
     @Override
-    public Builder setAvailIfSupported(boolean avail) {
+    public Builder setCommand(CommandName commandName, String phase, String subphase) {
-      return this;
+      getInstance().command = FeeExtensionCommandDescriptor.create(commandName, phase, subphase);
+      return thisCastToDerived();
     }
 
     @Override
-    public Builder setReasonIfSupported(String reason) {
+    public Builder setCurrencyIfSupported(CurrencyUnit currency) {
-      return this;
-    }
-
-    @Override
-    public FeeQueryResponseExtensionItem.Builder
-        setCurrencyIfSupported(CurrencyUnit currency) {
       getInstance().currency = currency;
       return this;
     }
-
-    @Override
-    public Builder setEffectiveDateIfSupported(DateTime effectiveDate) {
-      return this;
-    }
-
-    @Override
-    public Builder setNotAfterDateIfSupported(DateTime notAfterDate) {
-      return this;
-    }
   }
 }

java/google/registry/model/domain/fee06/FeeRenewCommandExtensionV06.java

@@ -14,8 +14,9 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import com.google.common.collect.ImmutableList;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImplNoCredits;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeRenewCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
@@ -23,11 +24,16 @@ import javax.xml.bind.annotation.XmlType;
 /** A fee extension that may be present on domain renew commands. */
 @XmlRootElement(name = "renew")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeRenewCommandExtensionV06
+public class FeeRenewCommandExtensionV06 extends FeeRenewCommandExtension {
-    extends FeeTransformCommandExtensionImplNoCredits implements FeeTransformCommandExtension {
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeRenewResponseExtensionV06.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeRenewResponseExtensionV06());
+  }
+
+  /** This version of the extension doesn't support the "credit" field. */
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return ImmutableList.of();
   }
 }

java/google/registry/model/domain/fee06/FeeRenewResponseExtensionV06.java

@@ -14,7 +14,9 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImplNoCredits;
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +26,11 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "renData")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeRenewResponseExtensionV06 extends FeeTransformResponseExtensionImplNoCredits {
+public class FeeRenewResponseExtensionV06 extends FeeTransformResponseExtension {
-  /** A builder for {@link FeeRenewResponseExtensionV06}. */
+
-  public static class Builder extends
+  /** This version of the extension doesn't support the "credit" field. */
-      FeeTransformResponseExtensionImplNoCredits.Builder<FeeRenewResponseExtensionV06, Builder> {}
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return super.getCredits();
+  }
 }

java/google/registry/model/domain/fee06/FeeTransferCommandExtensionV06.java

@@ -14,8 +14,9 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import com.google.common.collect.ImmutableList;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImplNoCredits;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeTransferCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
@@ -23,11 +24,16 @@ import javax.xml.bind.annotation.XmlType;
 /** A fee extension that may be present on domain transfer requests. */
 @XmlRootElement(name = "transfer")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeTransferCommandExtensionV06
+public class FeeTransferCommandExtensionV06 extends FeeTransferCommandExtension {
-    extends FeeTransformCommandExtensionImplNoCredits implements FeeTransformCommandExtension {
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeTransferResponseExtensionV06.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeTransferResponseExtensionV06());
+  }
+
+  /** This version of the extension doesn't support the "credit" field. */
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return ImmutableList.of();
   }
 }

java/google/registry/model/domain/fee06/FeeTransferResponseExtensionV06.java

@@ -14,7 +14,9 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImplNoCredits;
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,9 +26,11 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "trnData")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeTransferResponseExtensionV06 extends FeeTransformResponseExtensionImplNoCredits {
+public class FeeTransferResponseExtensionV06 extends FeeTransformResponseExtension {
-  /** A builder for {@link FeeTransferResponseExtensionV06}. */
+
-  public static class Builder
+  /** This version of the extension doesn't support the "credit" field. */
-      extends FeeTransformResponseExtensionImplNoCredits
+  @Override
-          .Builder<FeeTransferResponseExtensionV06, Builder> {}
+  public ImmutableList<Credit> getCredits() {
+    return super.getCredits();
+  }
 }

java/google/registry/model/domain/fee06/FeeUpdateCommandExtensionV06.java

@@ -14,20 +14,26 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import com.google.common.collect.ImmutableList;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImplNoCredits;
+import google.registry.model.domain.fee.Credit;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import google.registry.model.domain.fee.FeeUpdateCommandExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain update commands. */
 @XmlRootElement(name = "update")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeUpdateCommandExtensionV06
+public class FeeUpdateCommandExtensionV06 extends FeeUpdateCommandExtension {
-    extends FeeTransformCommandExtensionImplNoCredits implements FeeTransformCommandExtension {
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeUpdateResponseExtensionV06.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeUpdateResponseExtensionV06());
+  }
+
+  /** This version of the extension doesn't support the "credit" field. */
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return ImmutableList.of();
   }
 }

java/google/registry/model/domain/fee06/FeeUpdateResponseExtensionV06.java

@@ -14,7 +14,9 @@
 
 package google.registry.model.domain.fee06;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImplNoCredits;
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,9 +26,11 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "updData")
 @XmlType(propOrder = {"currency", "fees"})
-public class FeeUpdateResponseExtensionV06 extends FeeTransformResponseExtensionImplNoCredits {
+public class FeeUpdateResponseExtensionV06 extends FeeTransformResponseExtension {
-  /** A builder for {@link FeeUpdateResponseExtensionV06}. */
+
-  public static class Builder
+  /** This version of the extension doesn't support the "credit" field. */
-      extends FeeTransformResponseExtensionImplNoCredits
+  @Override
-          .Builder<FeeUpdateResponseExtensionV06, Builder> {}
+  public ImmutableList<Credit> getCredits() {
+    return super.getCredits();
+  }
 }

java/google/registry/model/domain/fee11/FeeCheckCommandExtensionV11.java

@@ -24,7 +24,6 @@ import google.registry.model.domain.Period;
 import google.registry.model.domain.fee.FeeCheckCommandExtension;
 import google.registry.model.domain.fee.FeeCheckCommandExtensionItem;
 import google.registry.model.domain.fee.FeeCheckResponseExtensionItem;
-import google.registry.model.domain.fee.FeeCheckResponseExtensionItem.Builder;
 import google.registry.model.domain.fee.FeeExtensionCommandDescriptor;
 import google.registry.model.domain.fee11.FeeCheckCommandExtensionV11.FeeCheckCommandExtensionItemV11;
 import javax.xml.bind.annotation.XmlElement;
@@ -88,7 +87,7 @@ public class FeeCheckCommandExtensionV11 extends ImmutableObject
   }
 
   /** Implementation of the item interface, returning values of the single "item". */
-  class FeeCheckCommandExtensionItemV11 implements FeeCheckCommandExtensionItem {
+  class FeeCheckCommandExtensionItemV11 extends FeeCheckCommandExtensionItem {
 
     /** The name of the command being checked. */
     @Override
@@ -135,7 +134,7 @@ public class FeeCheckCommandExtensionV11 extends ImmutableObject
     }
 
     @Override
-    public Builder createResponseBuilder() {
+    public FeeCheckResponseExtensionItemV11.Builder createResponseBuilder() {
       return new FeeCheckResponseExtensionItemV11.Builder();
     }
 

java/google/registry/model/domain/fee11/FeeCheckResponseExtensionItemV11.java

@@ -16,16 +16,15 @@ package google.registry.model.domain.fee11;
 
 import google.registry.model.domain.DomainObjectSpec;
 import google.registry.model.domain.fee.FeeCheckResponseExtensionItem;
-import google.registry.model.domain.fee.FeeQueryResponseExtensionItemImpl;
+import google.registry.model.domain.fee.FeeExtensionCommandDescriptor;
+import google.registry.model.domain.fee.FeeQueryCommandExtensionItem.CommandName;
 import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlType;
 import org.joda.money.CurrencyUnit;
-import org.joda.time.DateTime;
 
 /** The version 0.11 response for a domain check on a single resource. */
-@XmlType(propOrder = {"object", "command", "currency", "period", "fee", "feeClass", "reason"})
+@XmlType(propOrder = {"object", "command", "currency", "period", "fees", "feeClass", "reason"})
-public class FeeCheckResponseExtensionItemV11
+public class FeeCheckResponseExtensionItemV11 extends FeeCheckResponseExtensionItem {
-    extends FeeQueryResponseExtensionItemImpl implements FeeCheckResponseExtensionItem {
 
   /** Whether the domain is available. */
   @XmlAttribute
@@ -39,10 +38,18 @@ public class FeeCheckResponseExtensionItemV11
   /** The reason that the check item cannot be calculated. */
   String reason;
 
+  /** The command that was checked. */
+  FeeExtensionCommandDescriptor command;
+
   /** Builder for {@link FeeCheckResponseExtensionItemV11}. */
   public static class Builder
-      extends FeeQueryResponseExtensionItemImpl.Builder<FeeCheckResponseExtensionItemV11, Builder>
+    extends FeeCheckResponseExtensionItem.Builder<FeeCheckResponseExtensionItemV11> {
-      implements FeeCheckResponseExtensionItem.Builder {
+
+    @Override
+    public Builder setCommand(CommandName commandName, String phase, String subphase) {
+      getInstance().command = FeeExtensionCommandDescriptor.create(commandName, phase, subphase);
+      return this;
+    }
 
     @Override
     public Builder setDomainNameIfSupported(String name) {
@@ -67,15 +74,5 @@ public class FeeCheckResponseExtensionItemV11
       getInstance().reason = reason;
       return this;
     }
-
-    @Override
-    public Builder setEffectiveDateIfSupported(DateTime effectiveDate) {
-      return this;
-    }
-
-    @Override
-    public Builder setNotAfterDateIfSupported(DateTime notAfterDate) {
-      return this;
-    }
   }
 }

java/google/registry/model/domain/fee11/FeeCreateCommandExtensionV11.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeCreateCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain create commands. */
 @XmlRootElement(name = "create")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeCreateCommandExtensionV11
+public class FeeCreateCommandExtensionV11 extends FeeCreateCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeCreateResponseExtensionV11.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeCreateResponseExtensionV11());
   }
 }

java/google/registry/model/domain/fee11/FeeCreateResponseExtensionV11.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "creData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeCreateResponseExtensionV11 extends FeeTransformResponseExtensionImpl {
+public class FeeCreateResponseExtensionV11 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeCreateResponseExtensionV11}. */
-  public static class Builder
-      extends FeeTransformResponseExtensionImpl.Builder<FeeCreateResponseExtensionV11, Builder> {}
-}

java/google/registry/model/domain/fee11/FeeDeleteResponseExtensionV11.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,9 +24,12 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "delData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeDeleteResponseExtensionV11 extends FeeTransformResponseExtensionImpl {
+public class FeeDeleteResponseExtensionV11 extends FeeTransformResponseExtension {
 
   /** Builder for {@link FeeDeleteResponseExtensionV11}. */
-  public static class Builder
+  public static class Builder extends FeeTransformResponseExtension.Builder {
-      extends FeeTransformResponseExtensionImpl.Builder<FeeDeleteResponseExtensionV11, Builder> {}
+    public Builder() {
+      super(new FeeDeleteResponseExtensionV11());
+    }
+  }
 }

java/google/registry/model/domain/fee11/FeeRenewCommandExtensionV11.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeRenewCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain renew commands. */
 @XmlRootElement(name = "renew")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeRenewCommandExtensionV11
+public class FeeRenewCommandExtensionV11 extends FeeRenewCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeRenewResponseExtensionV11.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeRenewResponseExtensionV11());
   }
 }

java/google/registry/model/domain/fee11/FeeRenewResponseExtensionV11.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "renData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeRenewResponseExtensionV11 extends FeeTransformResponseExtensionImpl {
+public class FeeRenewResponseExtensionV11 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeRenewResponseExtensionV11}. */
-  public static class Builder
-      extends FeeTransformResponseExtensionImpl.Builder<FeeRenewResponseExtensionV11, Builder> {}
-}

java/google/registry/model/domain/fee11/FeeTransferCommandExtensionV11.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeTransferCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain transfer requests. */
 @XmlRootElement(name = "transfer")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeTransferCommandExtensionV11
+public class FeeTransferCommandExtensionV11 extends FeeTransferCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeTransferResponseExtensionV11.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeTransferResponseExtensionV11());
   }
 }

java/google/registry/model/domain/fee11/FeeTransferResponseExtensionV11.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "trnData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeTransferResponseExtensionV11 extends FeeTransformResponseExtensionImpl {
+public class FeeTransferResponseExtensionV11 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeTransferResponseExtensionV11}. */
-  public static class Builder
-     extends FeeTransformResponseExtensionImpl.Builder<FeeTransferResponseExtensionV11, Builder> {}
-}

java/google/registry/model/domain/fee11/FeeUpdateCommandExtensionV11.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import google.registry.model.domain.fee.FeeUpdateCommandExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain update commands. */
 @XmlRootElement(name = "update")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeUpdateCommandExtensionV11
+public class FeeUpdateCommandExtensionV11 extends FeeUpdateCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeUpdateResponseExtensionV11.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeUpdateResponseExtensionV11());
   }
 }

java/google/registry/model/domain/fee11/FeeUpdateResponseExtensionV11.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee11;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "updData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeUpdateResponseExtensionV11 extends FeeTransformResponseExtensionImpl {
+public class FeeUpdateResponseExtensionV11 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeUpdateResponseExtensionV11}. */
-  public static class Builder
-      extends FeeTransformResponseExtensionImpl.Builder<FeeUpdateResponseExtensionV11, Builder> {}
-}

java/google/registry/model/domain/fee12/FeeCheckCommandExtensionItemV12.java

@@ -17,10 +17,8 @@ package google.registry.model.domain.fee12;
 import com.google.common.base.Ascii;
 import com.google.common.base.CharMatcher;
 import com.google.common.base.Optional;
-import google.registry.model.ImmutableObject;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.fee.FeeCheckCommandExtensionItem;
-import google.registry.model.domain.fee.FeeCheckResponseExtensionItem;
 import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlType;
@@ -41,8 +39,7 @@ import org.joda.time.DateTime;
  * the names from the non-extension check element are used.
  */
 @XmlType(propOrder = {"period", "feeClass", "feeDate"})
-public class FeeCheckCommandExtensionItemV12
+public class FeeCheckCommandExtensionItemV12 extends FeeCheckCommandExtensionItem {
-    extends ImmutableObject implements FeeCheckCommandExtensionItem {
 
   /** The default validity period (if not specified) is 1 year for all operations. */
   static final Period DEFAULT_PERIOD = Period.create(1, Period.Unit.YEARS);
@@ -56,9 +53,6 @@ public class FeeCheckCommandExtensionItemV12
   @XmlAttribute
   String subphase;
 
-  @XmlElement
-  Period period;
-
   @XmlElement(name = "class")
   String feeClass;
 
@@ -110,12 +104,7 @@ public class FeeCheckCommandExtensionItemV12
   }
 
   @Override
-  public Period getPeriod() {
+  public FeeCheckResponseExtensionItemV12.Builder createResponseBuilder() {
-    return Optional.fromNullable(period).or(DEFAULT_PERIOD);
-  }
-
-  @Override
-  public FeeCheckResponseExtensionItem.Builder createResponseBuilder() {
     return new FeeCheckResponseExtensionItemV12.Builder();
   }
 

java/google/registry/model/domain/fee12/FeeCheckResponseExtensionItemV12.java

@@ -17,24 +17,19 @@ package google.registry.model.domain.fee12;
 import static google.registry.util.CollectionUtils.forceEmptyToNull;
 
 import com.google.common.collect.ImmutableList;
-import google.registry.model.Buildable.GenericBuilder;
-import google.registry.model.ImmutableObject;
 import google.registry.model.domain.DomainObjectSpec;
 import google.registry.model.domain.Period;
 import google.registry.model.domain.fee.Fee;
 import google.registry.model.domain.fee.FeeCheckResponseExtensionItem;
 import google.registry.model.domain.fee.FeeQueryCommandExtensionItem.CommandName;
-import java.util.List;
 import javax.xml.bind.annotation.XmlType;
-import org.joda.money.CurrencyUnit;
 import org.joda.time.DateTime;
 
 /**
  * The version 0.12 response for a domain check on a single resource.
  */
 @XmlType(propOrder = {"object", "command"})
-public class FeeCheckResponseExtensionItemV12
+public class FeeCheckResponseExtensionItemV12 extends FeeCheckResponseExtensionItem {
-    extends ImmutableObject implements FeeCheckResponseExtensionItem {
 
   /** The domain that was checked. */
   DomainObjectSpec object;
@@ -42,6 +37,28 @@ public class FeeCheckResponseExtensionItemV12
   /** The command that was checked. */
   FeeCheckResponseExtensionItemCommandV12 command;
 
+  /**
+   * This method is overridden and not annotated for JAXB because this version of the extension
+   * doesn't support "period".
+   */
+  @Override
+  public Period getPeriod() {
+    return super.getPeriod();
+  }
+
+  /**
+   * This method is overridden and not annotated for JAXB because this version of the extension
+   * doesn't support "fee".
+   */
+  @Override
+  public ImmutableList<Fee> getFees() {
+    return super.getFees();
+  }
+
+  /**
+   * This method is not annotated for JAXB because this version of the extension doesn't support
+   * "feeClass" and because the data comes off of the command object rather than a field.
+   */
   @Override
   public String getFeeClass() {
     return command.getFeeClass();
@@ -49,15 +66,10 @@ public class FeeCheckResponseExtensionItemV12
 
   /** Builder for {@link FeeCheckResponseExtensionItemV12}. */
   public static class Builder
-      extends GenericBuilder<FeeCheckResponseExtensionItemV12, Builder>
+      extends FeeCheckResponseExtensionItem.Builder<FeeCheckResponseExtensionItemV12> {
-      implements FeeCheckResponseExtensionItem.Builder {
 
-    final FeeCheckResponseExtensionItemCommandV12.Builder commandBuilder;
+    final FeeCheckResponseExtensionItemCommandV12.Builder commandBuilder =
-
+        new FeeCheckResponseExtensionItemCommandV12.Builder();
-    Builder() {
-      super();
-      commandBuilder = new FeeCheckResponseExtensionItemCommandV12.Builder();
-    }
 
     @Override
     public Builder setCommand(CommandName commandName, String phase, String subphase) {
@@ -74,7 +86,7 @@ public class FeeCheckResponseExtensionItemV12
     }
 
     @Override
-    public Builder setFees(List<Fee> fees) {
+    public Builder setFees(ImmutableList<Fee> fees) {
       commandBuilder.setFee(forceEmptyToNull(ImmutableList.copyOf(fees)));
       return this;
     }
@@ -91,22 +103,6 @@ public class FeeCheckResponseExtensionItemV12
       return this;
     }
 
-    /** Version 0.12 does not support currency in check items. */
-    @Override
-    public Builder setCurrencyIfSupported(CurrencyUnit currency) {
-      return this;
-    }
-
-    @Override
-    public Builder setAvailIfSupported(boolean avail) {
-      return this;
-    }
-
-    @Override
-    public Builder setReasonIfSupported(String reason) {
-      return this;
-    }
-
     @Override
     public FeeCheckResponseExtensionItemV12 build() {
       getInstance().command = commandBuilder.build();

java/google/registry/model/domain/fee12/FeeCreateCommandExtensionV12.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeCreateCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain create commands. */
 @XmlRootElement(name = "create")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeCreateCommandExtensionV12
+public class FeeCreateCommandExtensionV12 extends FeeCreateCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeCreateResponseExtensionV12.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeCreateResponseExtensionV12());
   }
 }

java/google/registry/model/domain/fee12/FeeCreateResponseExtensionV12.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "creData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeCreateResponseExtensionV12 extends FeeTransformResponseExtensionImpl {
+public class FeeCreateResponseExtensionV12 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeCreateResponseExtensionV12}. */
-  public static class Builder
-      extends FeeTransformResponseExtensionImpl.Builder<FeeCreateResponseExtensionV12, Builder> {}
-}

java/google/registry/model/domain/fee12/FeeDeleteResponseExtensionV12.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,9 +24,12 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "delData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeDeleteResponseExtensionV12 extends FeeTransformResponseExtensionImpl {
+public class FeeDeleteResponseExtensionV12 extends FeeTransformResponseExtension {
 
   /** Builder for {@link FeeDeleteResponseExtensionV12}. */
-  public static class Builder
+  public static class Builder extends FeeTransformResponseExtension.Builder {
-      extends FeeTransformResponseExtensionImpl.Builder<FeeDeleteResponseExtensionV12, Builder> {}
+    public Builder() {
+      super(new FeeDeleteResponseExtensionV12());
+    }
+  }
 }

java/google/registry/model/domain/fee12/FeeRenewCommandExtensionV12.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeRenewCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain renew commands. */
 @XmlRootElement(name = "renew")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeRenewCommandExtensionV12
+public class FeeRenewCommandExtensionV12  extends FeeRenewCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeRenewResponseExtensionV12.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeRenewResponseExtensionV12());
   }
 }

java/google/registry/model/domain/fee12/FeeRenewResponseExtensionV12.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "renData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeRenewResponseExtensionV12 extends FeeTransformResponseExtensionImpl {
+public class FeeRenewResponseExtensionV12 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeRenewResponseExtensionV12}. */
-  public static class Builder
-      extends FeeTransformResponseExtensionImpl.Builder<FeeRenewResponseExtensionV12, Builder> {}
-}

java/google/registry/model/domain/fee12/FeeTransferCommandExtensionV12.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
+import google.registry.model.domain.fee.FeeTransferCommandExtension;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain transfer requests. */
 @XmlRootElement(name = "transfer")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeTransferCommandExtensionV12
+public class FeeTransferCommandExtensionV12 extends FeeTransferCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeTransferResponseExtensionV12.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeTransferResponseExtensionV12());
   }
 }

java/google/registry/model/domain/fee12/FeeTransferResponseExtensionV12.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "trnData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeTransferResponseExtensionV12 extends FeeTransformResponseExtensionImpl {
+public class FeeTransferResponseExtensionV12 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeTransferResponseExtensionV12}. */
-  public static class Builder
-      extends FeeTransformResponseExtensionImpl.Builder<FeeTransferResponseExtensionV12, Builder> {}
-}

java/google/registry/model/domain/fee12/FeeUpdateCommandExtensionV12.java

@@ -14,20 +14,32 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformCommandExtension;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
-import google.registry.model.domain.fee.FeeTransformCommandExtensionImpl;
+
+import com.google.common.collect.ImmutableList;
+import google.registry.model.domain.fee.Credit;
 import google.registry.model.domain.fee.FeeTransformResponseExtension;
+import google.registry.model.domain.fee.FeeUpdateCommandExtension;
+import java.util.List;
+import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
 /** A fee extension that may be present on domain update commands. */
 @XmlRootElement(name = "update")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeUpdateCommandExtensionV12
+public class FeeUpdateCommandExtensionV12 extends FeeUpdateCommandExtension {
-    extends FeeTransformCommandExtensionImpl implements FeeTransformCommandExtension {
+
+  @XmlElement(name = "credit")
+  List<Credit> credits;
+
+  @Override
+  public ImmutableList<Credit> getCredits() {
+    return nullToEmptyImmutableCopy(credits);
+  }
 
   @Override
   public FeeTransformResponseExtension.Builder createResponseBuilder() {
-    return new FeeUpdateResponseExtensionV12.Builder();
+    return new FeeTransformResponseExtension.Builder(new FeeUpdateResponseExtensionV12());
   }
 }

java/google/registry/model/domain/fee12/FeeUpdateResponseExtensionV12.java

@@ -14,7 +14,7 @@
 
 package google.registry.model.domain.fee12;
 
-import google.registry.model.domain.fee.FeeTransformResponseExtensionImpl;
+import google.registry.model.domain.fee.FeeTransformResponseExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 
@@ -24,8 +24,4 @@ import javax.xml.bind.annotation.XmlType;
  */
 @XmlRootElement(name = "updData")
 @XmlType(propOrder = {"currency", "fees", "credits"})
-public class FeeUpdateResponseExtensionV12 extends FeeTransformResponseExtensionImpl {
+public class FeeUpdateResponseExtensionV12 extends FeeTransformResponseExtension {}
-  /** A builder for {@link FeeUpdateResponseExtensionV12}. */
-  public static class Builder
-      extends FeeTransformResponseExtensionImpl.Builder<FeeUpdateResponseExtensionV12, Builder> {}
-}

java/google/registry/model/eppinput/EppInput.java

@@ -17,7 +17,6 @@ package google.registry.model.eppinput;
 import static google.registry.util.CollectionUtils.nullSafeImmutableCopy;
 import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
 
-import com.google.common.base.Optional;
 import com.google.common.collect.FluentIterable;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -111,34 +110,6 @@ public class EppInput extends ImmutableObject {
     return FluentIterable.from(getCommandWrapper().getExtensions()).filter(clazz).first().orNull();
   }
 
-  /** Get the extension based on type, or null, chosen from a list of possible extension classes.
-   * If there are extensions matching multiple classes, the first class listed is chosen. If there
-   * are multiple extensions of the same class, the first extension of that class is chosen
-   * (assuming that an extension matching a preceding class was not already chosen). This method is
-   * used to support multiple versions of an extension. Specify all supported versions, starting
-   * with the latest. The first-occurring extension of the latest version will be chosen, or failing
-   * that the first-occurring extension of the previous version, and so on.
-   */
-  @Nullable
-  public <E extends CommandExtension>
-      E getFirstExtensionOfClasses(ImmutableList<Class<? extends E>> classes) {
-    for (Class<? extends E> clazz : classes) {
-      Optional<? extends E> extension = FluentIterable.from(
-          getCommandWrapper().getExtensions()).filter(clazz).first();
-      if (extension.isPresent()) {
-        return extension.get();
-      }
-    }
-    return null;
-  }
-
-  @SafeVarargs
-  @Nullable
-  public final <E extends CommandExtension>
-      E getFirstExtensionOfClasses(Class<? extends E>... classes) {
-    return getFirstExtensionOfClasses(ImmutableList.copyOf(classes));
-  }
-
   /** A tag that goes inside of an EPP {@literal <command>}. */
   public static class InnerCommand extends ImmutableObject {}
 

java/google/registry/tools/server/VerifyOteAction.java

@@ -18,7 +18,6 @@ import static com.google.common.base.Predicates.not;
 import static com.google.common.collect.Maps.toMap;
 import static google.registry.flows.EppXmlTransformer.unmarshal;
 import static google.registry.flows.picker.FlowPicker.getFlowClass;
-import static google.registry.model.domain.fee.Fee.FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.util.CollectionUtils.isNullOrEmpty;
 import static google.registry.util.DomainNameUtils.ACE_PREFIX;
@@ -58,6 +57,7 @@ import google.registry.flows.host.HostCreateFlow;
 import google.registry.flows.host.HostDeleteFlow;
 import google.registry.flows.host.HostUpdateFlow;
 import google.registry.model.domain.DomainCommand;
+import google.registry.model.domain.fee.FeeCreateCommandExtension;
 import google.registry.model.domain.launch.LaunchCreateExtension;
 import google.registry.model.domain.secdns.SecDnsCreateExtension;
 import google.registry.model.domain.secdns.SecDnsUpdateExtension;
@@ -143,8 +143,7 @@ public class VerifyOteAction implements Runnable, JsonAction {
   private static final Predicate<EppInput> HAS_FEE = new Predicate<EppInput>() {
       @Override
       public boolean apply(@Nonnull EppInput eppInput) {
-        return eppInput.getFirstExtensionOfClasses(
+        return eppInput.getSingleExtension(FeeCreateCommandExtension.class) != null;
-            FEE_CREATE_COMMAND_EXTENSIONS_IN_PREFERENCE_ORDER) != null;
       }};
 
   private static final Predicate<EppInput> HAS_SEC_DNS = new Predicate<EppInput>() {

javatests/google/registry/flows/ExtensionManagerTest.java

@@ -24,7 +24,6 @@ import google.registry.flows.ExtensionManager.UndeclaredServiceExtensionExceptio
 import google.registry.flows.ExtensionManager.UnsupportedRepeatedExtensionException;
 import google.registry.flows.exceptions.OnlyToolCanPassMetadataException;
 import google.registry.flows.session.HelloFlow;
-import google.registry.model.domain.allocate.AllocateCreateExtension;
 import google.registry.model.domain.fee06.FeeInfoCommandExtensionV06;
 import google.registry.model.domain.launch.LaunchCreateExtension;
 import google.registry.model.domain.metadata.MetadataExtension;
@@ -68,23 +67,6 @@ public class ExtensionManagerTest {
     manager.validate();
   }
 
-  @Test
-  public void testMultipleExtensionsFromSameGroupForbidden() throws Exception {
-    ExtensionManager manager = new TestInstanceBuilder()
-        .setEppRequestSource(EppRequestSource.TOOL)
-        .setDeclaredUris(ServiceExtension.FEE_0_6.getUri())
-        .setSuppliedExtensions(
-            MetadataExtension.class,
-            LaunchCreateExtension.class,
-            AllocateCreateExtension.class)
-        .build();
-    manager.register(MetadataExtension.class);
-    manager.registerAsGroup(
-        ImmutableList.of(LaunchCreateExtension.class, AllocateCreateExtension.class));
-    thrown.expect(UnsupportedRepeatedExtensionException.class);
-    manager.validate();
-  }
-
   @Test
   public void testUndeclaredExtensionsLogged() throws Exception {
     TestLogHandler handler = new TestLogHandler();