Import code from internal repository to git

java/com/google/domain/registry/model/BackupGroupRoot.java

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+// Copyright 2016 Google Inc. 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 com.google.domain.registry.model;
+
+import com.google.domain.registry.model.EppResource.SharedFields;
+
+import javax.xml.bind.annotation.XmlTransient;
+
+/**
+ * Base class for entities that are the root of a Registry 2.0 entity group that gets enrolled in
+ * commit logs for backup purposes.
+ *
+ * <p>The commit log system needs to preserve the ordering of closely timed mutations to entities
+ * in a single entity group. We require an {@link UpdateAutoTimestamp} field on the root of a group
+ * so that we can enforce strictly increasing timestamps.
+ */
+public abstract class BackupGroupRoot extends ImmutableObject {
+  /**
+   * An automatically managed timestamp of when this object was last written to datastore.
+   *
+   * <p>Note that this is distinct from the EPP-specified {@link SharedFields#lastUpdateTime} on
+   * {@link EppResource} objects, in that it is updated on every save, rather than just in response
+   * to an {@code <update>} command.
+   */
+  @XmlTransient
+  UpdateAutoTimestamp updateTimestamp = UpdateAutoTimestamp.create(null);
+
+  /** Get the {@link UpdateAutoTimestamp} for this entity. */
+  public final UpdateAutoTimestamp getUpdateAutoTimestamp() {
+    return updateTimestamp;
+  }
+}