BUG-5280: centralize ShardSnapshot operations

[controller.git] / opendaylight / md-sal / sal-distributed-datastore / src / main / java / org / opendaylight / controller / cluster / datastore / persisted / ShardDataTreeSnapshotMetadata.java

diff --git a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/persisted/ShardDataTreeSnapshotMetadata.java b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/persisted/ShardDataTreeSnapshotMetadata.java
new file mode 100644 (file)
index 0000000..a20ec4e
--- /dev/null
+++ b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/persisted/ShardDataTreeSnapshotMetadata.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2016 Cisco Systems, Inc. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.opendaylight.controller.cluster.datastore.persisted;
+
+import com.google.common.base.Verify;
+import java.io.Externalizable;
+import java.io.Serializable;
+import javax.annotation.Nonnull;
+
+/**
+ * Base class for various bits of metadata attached to a {@link MetadataShardDataTreeSnapshot}. This class is not
+ * an interface because we want to make sure all subclasses implement the externalizable proxy pattern, for which
+ * we need to force {@link #readResolve()} to be abstract.
+ *
+ * All concrete subclasses of this class should be final so as to form a distinct set of possible metadata. Since
+ * metadata is serialized along with {@link MetadataShardDataTreeSnapshot}, this set is part of the serialization format
+ * guarded by {@link PayloadVersion}.
+ *
+ * If a new metadata type is introduced or a type is removed, {@link PayloadVersion} needs to be bumped to ensure
+ * compatibility.
+ *
+ * @author Robert Varga
+ */
+public abstract class ShardDataTreeSnapshotMetadata implements Serializable {
+    private static final long serialVersionUID = 1L;
+
+    ShardDataTreeSnapshotMetadata() {
+        // Prevent subclassing from outside of this package
+    }
+
+    final Object writeReplace() {
+        return Verify.verifyNotNull(externalizableProxy(), "Null externalizable proxy from %s", getClass());
+    }
+
+    /**
+     * Return an Externalizable proxy
+     *
+     * @return Externalizable proxy, may not be null
+     */
+    protected abstract @Nonnull Externalizable externalizableProxy();
+}