Messaging facade for clustered communications to allow implementations from JGroups or Hazelcast to be used.

* PropertyBackedBeanExporter uses the facade, configured with JGroups messaging implementation.
* Unfortunately, some remodelling required before this will work with Ehcache's CacheManagerPeerProviderFactory




git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@33830 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/cluster/JGroupsMessenger.java

@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2005-2012 Alfresco Software Limited.
+ *
+ * This file is part of Alfresco
+ *
+ * Alfresco is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Alfresco is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with Alfresco. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.alfresco.repo.cluster;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectInput;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutput;
+import java.io.ObjectOutputStream;
+import java.io.Serializable;
+
+import org.jgroups.Channel;
+import org.jgroups.Message;
+import org.jgroups.ReceiverAdapter;
+
+/**
+ * JGroups implementation of the {@link Messenger} class.
+ * 
+ * @author Matt Ward
+ */
+public class JGroupsMessenger<T extends Serializable> extends ReceiverAdapter implements Messenger<T>
+{
+    private final Channel channel;
+    private MessageReceiver<T> receiverDelegate;
+    
+    
+    /**
+     * Construct a messenger that wraps a JGroups Channel.
+     * 
+     * @param channel
+     */
+    public JGroupsMessenger(Channel channel)
+    {
+        this.channel = channel;
+    }
+
+    
+    @Override
+    public void send(T message)
+    {
+        try
+        {
+            // Serializing the message ourselves and passing a byte[]
+            // to Channel.send() as recommended by JGroups.
+            ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+            ObjectOutput out = new ObjectOutputStream(bytes);
+            out.writeObject(message);
+            out.close();
+            bytes.close();
+            channel.send(null, null, bytes.toByteArray());
+        }
+        catch (Throwable e)
+        {
+            throw new MessageSendingException(e);
+        }
+    }
+
+    /*
+     * @see org.alfresco.repo.cluster.Messenger#setReceiver(org.alfresco.repo.cluster.MessageReceiver)
+     */
+    @Override
+    public void setReceiver(MessageReceiver<T> receiver)
+    {
+        // Make sure the delegate is installed, before starting to receive messages.
+        receiverDelegate = receiver;
+        // Start receiving messages and dispatch them to the delegate.
+        channel.setReceiver(this);
+    }
+
+
+    /*
+     * @see org.jgroups.ReceiverAdapter#receive(org.jgroups.Message)
+     */
+    @Override
+    public void receive(Message msg)
+    {
+        // Deserializing the message ourselves rather than using
+        // the Message's getObject() method (as recommended by JGroups).
+        byte[] msgBytes = msg.getBuffer();
+        ByteArrayInputStream bytes = new ByteArrayInputStream(msgBytes);
+        ObjectInput in;
+        try
+        {
+            in = new ObjectInputStream(bytes);
+            @SuppressWarnings("unchecked")
+            T payload = (T) in.readObject();
+            in.close();
+            bytes.close();
+            // Pass the deserialized payload on to the receiver delegate
+            receiverDelegate.onReceive(payload);
+        }
+        catch (IOException e)
+        {
+            throw new RuntimeException("Couldn't receive object.", e);
+        }
+        catch (ClassNotFoundException e)
+        {
+            throw new RuntimeException("Couldn't receive object.", e);
+        }
+    }
+
+
+    @Override
+    public boolean isConnected()
+    {
+        return channel.isConnected();
+    }
+}