上文http://nod0620.iteye.com/admin/blogs/1030398 写了session复制的发送部分，继续接收部分：
当接收方tomcat接收到需要session的消息时，最终调用了GroupChannel的messageReceived()方法
public void messageReceived(ChannelMessage msg) {
if ( msg == null ) return;
try {
if ( Logs.MESSAGES.isTraceEnabled() ) {
Logs.MESSAGES.trace("GroupChannel - Received msg:" + new UniqueId(msg.getUniqueId()) + " at " +new java.sql.Timestamp(System.currentTimeMillis())+ " from "+msg.getAddress().getName());
}
Serializable fwd = null;
if ( (msg.getOptions() & SEND_OPTIONS_BYTE_MESSAGE) == SEND_OPTIONS_BYTE_MESSAGE ) {
fwd = new ByteMessage(msg.getMessage().getBytes());
} else {
try {
fwd = XByteBuffer.deserialize(msg.getMessage().getBytesDirect(), 0, msg.getMessage().getLength());
}catch (Exception sx) {
log.error("Unable to deserialize message:"+msg,sx);
return;
}
}
if ( Logs.MESSAGES.isTraceEnabled() ) {
Logs.MESSAGES.trace("GroupChannel - Receive Message:" + new UniqueId(msg.getUniqueId()) + " is " +fwd);
}
//get the actual member with the correct alive time
Member source = msg.getAddress();
boolean rx = false;
boolean delivered = false;
for ( int i=0; i<channelListeners.size(); i++ ) {
ChannelListener channelListener = (ChannelListener)channelListeners.get(i);
if (channelListener != null && channelListener.accept(fwd, source)) {
channelListener.messageReceived(fwd, source);
delivered = true;
//if the message was accepted by an RPC channel, that channel
//is responsible for returning the reply, otherwise we send an absence reply
if ( channelListener instanceof RpcChannel ) rx = true;
}
}//for
if ((!rx) && (fwd instanceof RpcMessage)) {
//if we have a message that requires a response,
//but none was given, send back an immediate one
sendNoRpcChannelReply((RpcMessage)fwd,source);
}
if ( Logs.MESSAGES.isTraceEnabled() ) {
Logs.MESSAGES.trace("GroupChannel delivered["+delivered+"] id:"+new UniqueId(msg.getUniqueId()));
}
} catch ( Exception x ) {
//this could be the channel listener throwing an exception, we should log it
//as a warning.
if ( log.isWarnEnabled() ) log.warn("Error receiving message:",x);
throw new RemoteProcessException("Exception:"+x.getMessage(),x);
}
}
可以看到，这里主要是调用ChannelListener的messageReceived方法，显然这个实现类就是SimpleTcpCluster：
public void messageReceived(Serializable message, Member sender) {
ClusterMessage fwd = (ClusterMessage)message;
fwd.setAddress(sender);
messageReceived(fwd);
}
public void messageReceived(ClusterMessage message) {
long start = 0;
if (log.isDebugEnabled() && message != null)
log.debug("Assuming clocks are synched: Replication for "
+ message.getUniqueId() + " took="
+ (System.currentTimeMillis() - (message).getTimestamp())
+ " ms.");
//invoke all the listeners
boolean accepted = false;
if (message != null) {
for (Iterator iter = clusterListeners.iterator(); iter.hasNext();) {
ClusterListener listener = (ClusterListener) iter.next();
if (listener.accept(message)) {
accepted = true;
listener.messageReceived(message);
}
}
}
if (!accepted && log.isDebugEnabled()) {
if (notifyLifecycleListenerOnFailure) {
Member dest = message.getAddress();
// Notify our interested LifecycleListeners
lifecycle.fireLifecycleEvent(RECEIVE_MESSAGE_FAILURE_EVENT,
new SendMessageData(message, dest, null));
}
log.debug("Message " + message.toString() + " from type "
+ message.getClass().getName()
+ " transfered but no listener registered");
}
return;
}
其实这里调用的是ClusterListener的messageReceived()方法，默认的两个ClusterListener是ClusterSessionListener和JvmRouteSessionIDBinderListener，JvmRouteSessionIDBinderListener只有在发送的消息是关于session id改变的消息时才起作用，重点看ClusterSessionListener.messageReceived()方法，其实是调用到了DeltaManager的messageDataReceived()方法：
public void messageDataReceived(ClusterMessage cmsg) {
if (cmsg != null && cmsg instanceof SessionMessage) {
SessionMessage msg = (SessionMessage) cmsg;
switch (msg.getEventType()) {
case SessionMessage.EVT_GET_ALL_SESSIONS:
case SessionMessage.EVT_SESSION_CREATED:
case SessionMessage.EVT_SESSION_EXPIRED:
case SessionMessage.EVT_SESSION_ACCESSED:
case SessionMessage.EVT_SESSION_DELTA:
case SessionMessage.EVT_CHANGE_SESSION_ID: {
synchronized(receivedMessageQueue) {
if(receiverQueue) {
receivedMessageQueue.add(msg);
return ;
}
}
break;
}
default: {
//we didn't queue, do nothing
break;
}
} //switch
messageReceived(msg, msg.getAddress() != null ? (Member) msg.getAddress() : null);
}
}
这里的事件是EVT_GET_ALL_SESSIONS，在messageReceived()方法中有这个分支的处理代码，最后面调用
handleGET_ALL_SESSIONS()方法：
protected void handleGET_ALL_SESSIONS(SessionMessage msg, Member sender) throws IOException {
counterReceive_EVT_GET_ALL_SESSIONS++;
//get a list of all the session from this manager
if (log.isDebugEnabled()) log.debug(sm.getString("deltaManager.receiveMessage.unloadingBegin", getName()));
// Write the number of active sessions, followed by the details
// get all sessions and serialize without sync
Session[] currentSessions = findSessions();
long findSessionTimestamp = System.currentTimeMillis() ;
if (isSendAllSessions()) {
sendSessions(sender, currentSessions, findSessionTimestamp);
} else {
// send session at blocks
for (int i = 0; i < currentSessions.length; i += getSendAllSessionsSize()) {
int len = i + getSendAllSessionsSize() > currentSessions.length ? currentSessions.length - i : getSendAllSessionsSize();
Session[] sendSessions = new Session[len];
System.arraycopy(currentSessions, i, sendSessions, 0, len);
sendSessions(sender, sendSessions,findSessionTimestamp);
if (getSendAllSessionsWaitTime() > 0) {
try {
Thread.sleep(getSendAllSessionsWaitTime());
} catch (Exception sleep) {
}
}//end if
}//for
}//end if
SessionMessage newmsg = new SessionMessageImpl(name,SessionMessage.EVT_ALL_SESSION_TRANSFERCOMPLETE, null,"SESSION-STATE-TRANSFERED", "SESSION-STATE-TRANSFERED"+ getName());
newmsg.setTimestamp(findSessionTimestamp);
if (log.isDebugEnabled()) log.debug(sm.getString("deltaManager.createMessage.allSessionTransfered",getName()));
counterSend_EVT_ALL_SESSION_TRANSFERCOMPLETE++;
cluster.send(newmsg, sender);
}
主要是先找到所有的session，然后发送所有的session，然后发送一个标志结束的消息表示发送完成。这样第一次tomcat的启动加入集群是拿所用的session就完成了，主要的流程是这样的：
发送方：
StandardContext.start()--->SimpleTcpCluster.createManager()--->StandardContext.setManager()--->
DeltaManager.start()--->DeltaManager.getAllClusterSessions()--->SimpleTcpCluster.send()
---->GroupChannel.send()---->ParallelNioSender.sendMessage()--->NioSender.process()
接收方：
NioReceiver.listen()--->NioReceiver.readDataFromSocket()---->NioReplicationTask.drainChannel()--->
ListenCallback.messageDataReceived()---->ChannelCoordinator.messageReceived()--->
GroupChannel.messageReceived()--->SimpleTcpCluster.messageReceived()--->
DeltaManager.messageDataReceived()---->DeltaManager.handleGET_ALL_SESSIONS()
接收方准备好数据又要发送给发送方，简单来说通信是这样：
发送方发送请求--->接收方接受请求，发送数据，一个是session的数据，一个是session发送完毕的数据--->
发送方收到接收方过来的两种数据