Zookeeper-watcher机制源码分析（二）

在前一篇文章中Zookeeper-watcher机制源码分析（一）说过Watcher的基本流程，在此文中详细剖析服务端几首请求处理流程。

服务端有一个NettyServerCnxn类，用来处理客户端发送过来的请求 

NettyServerCnxn 

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public void receiveMessage(ChannelBuffer message) {         try {             while(message.readable() && !throttled) {                 if (bb != null) { //ByteBuffer不为空                     if (LOG.isTraceEnabled()) {                         LOG.trace("message readable " + message.readableBytes()                                 + " bb len " + bb.remaining() + " " + bb);                         ByteBuffer dat = bb.duplicate();                         dat.flip();                         LOG.trace(Long.toHexString(sessionId)                                 + " bb 0x"                                 + ChannelBuffers.hexDump(                                         ChannelBuffers.copiedBuffer(dat)));                     }                     //bb剩余空间大于message中可读字节大小                     if (bb.remaining() > message.readableBytes()) {                         int newLimit = bb.position() + message.readableBytes();                         bb.limit(newLimit);                     }                     // 将message写入bb中                     message.readBytes(bb);                     bb.limit(bb.capacity());                       if (LOG.isTraceEnabled()) {                         LOG.trace("after readBytes message readable "                                 + message.readableBytes()                                 + " bb len " + bb.remaining() + " " + bb);                         ByteBuffer dat = bb.duplicate();                         dat.flip();                         LOG.trace("after readbytes "                                 + Long.toHexString(sessionId)                                 + " bb 0x"                                 + ChannelBuffers.hexDump(                                         ChannelBuffers.copiedBuffer(dat)));                     }                     if (bb.remaining() == 0) { // 已经读完message，表示内容已经全部接收                         packetReceived(); // 统计接收信息                         bb.flip();                           ZooKeeperServer zks = this.zkServer;                         if (zks == null || !zks.isRunning()) { //Zookeeper服务器为空 ,说明服务端挂了                             throw new IOException("ZK down");                         }                         if (initialized) {                             //处理客户端传过来的数据包                             zks.processPacket(this, bb);                               if (zks.shouldThrottle(outstandingCount.incrementAndGet())) {                                 disableRecvNoWait();                             }                         } else {                             LOG.debug("got conn req request from "                                     + getRemoteSocketAddress());                             zks.processConnectRequest(this, bb);                             initialized = true;                         }                         bb = null;                     }                 } else { //bb为null的情况，大家自己去看，我就不细讲了                     if (LOG.isTraceEnabled()) {                         LOG.trace("message readable "                                 + message.readableBytes()                                 + " bblenrem " + bbLen.remaining());                         ByteBuffer dat = bbLen.duplicate();                         dat.flip();                         LOG.trace(Long.toHexString(sessionId)                                 +