Add XjcToContactResourceConverter

XjcToContactResourceConverter is, as it name suggests, an inverse of
ContactResourceToXjcConverter. This utility class is designed to
support the TLD data import feature.

EXTERNAL_REVIEW_URL=https://github.com/google/domain-registry/pull/19
GIT_AUTHOR=Wolfgang Meyers <wolfgang@donuts.co>
(With some minor changes by Ben McIlwain.)
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125985714

java/google/registry/util/XmlToEnumMapper.java

@@ -0,0 +1,55 @@
+// Copyright 2016 The Domain Registry 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.util;
+
+import com.google.common.collect.ImmutableMap;
+
+import javax.xml.bind.annotation.XmlEnumValue;
+
+/** Efficient lookup from xml enums to java enums */
+public final class XmlToEnumMapper<T extends Enum<?>> {
+
+  private final ImmutableMap<String, T> map;
+
+  /** Look up T from the {@link XmlEnumValue} */
+  public T xmlToEnum(String value) {
+    return map.get(value);
+  }
+
+  /**
+   * Creates a new {@link XmlToEnumMapper} from xml value to enum value.
+   */
+  public static <T extends Enum<?>> XmlToEnumMapper<T> create(T[] enumValues) {
+    return new XmlToEnumMapper<T>(enumValues);
+  }
+
+  private XmlToEnumMapper(T[] enumValues) {
+    ImmutableMap.Builder<String, T> mapBuilder = new ImmutableMap.Builder<>();
+    for (T value : enumValues) {
+      try {
+        String xmlName =
+            value
+                .getDeclaringClass()
+                .getField(value.name())
+                .getAnnotation(XmlEnumValue.class)
+                .value();
+        mapBuilder = mapBuilder.put(xmlName, value);
+      } catch (NoSuchFieldException e) {
+        throw new RuntimeException(e);
+      }
+    }
+    map = mapBuilder.build();
+  }
+}