利用netty实现支持高并发的Tcp短连接接收服务

      如果你对Netty有所了解，我们利用Netty写Tcp服务时，通常会继承SimpleChannelUpstreamHandler类，重写messageReceived函数进行数据的接收，如下就是个简单的tcp短连接服务样例：

public class TelnetServerHandler extends SimpleChannelUpstreamHandler {

    private static final Logger logger = Logger.getLogger(
            TelnetServerHandler.class.getName());

    @Override
    public void handleUpstream(
            ChannelHandlerContext ctx, ChannelEvent e) throws Exception {
        if (e instanceof ChannelStateEvent) {
            logger.info(e.toString());
        }
        super.handleUpstream(ctx, e);
    }

    @Override
    public void channelConnected(
            ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
        // Send greeting for a new connection.
        e.getChannel().write(
                "Welcome to " + InetAddress.getLocalHost().getHostName() + "!\r\n");
        e.getChannel().write("It is " + new Date() + " now.\r\n");
    }

    @Override
    public void messageReceived(
            ChannelHandlerContext ctx, MessageEvent e) {

        String request = (String) e.getMessage();

        // Generate and write a response.
        String response;
        boolean close = false;
        if (request.length() == 0) {
            response = "Please type something.\r\n";
        } else if (request.toLowerCase().equals("bye")) {
            response = "Have a good day!\r\n";
            close = true;
        } else {
            response = "Did you say '" + request + "'?\r\n";
        }

        // We do not need to write a ChannelBuffer here.
        // We know the encoder inserted at TelnetPipelineFactory will do the conversion.
        ChannelFuture future = e.getChannel().write(response);
        if (close) {
            future.addListener(ChannelFutureListener.CLOSE);
        }
    }
}

   

      但是，如果有高并发用户，数据发送出现乱序。例如有A用户发送1--2--3--4--5--6，B用户发送a--b--c--d--e--f。而服务端接收的数据顺序可能是：1--2--a--b--3--4--c--d---e---f---5---6。
     所以为了支持高并发的用户，不合适采用单线程接收用户数据的机制，应该实现支持异步的数据接收；并且为每个连接通道建立状态来进行缓冲数据的维护，直至客户端关闭时,将接收的数据给业务层去处理,如下面 receiver.receive(receivedBytes)函数。

     下面是个简单的实现：

    public class ChannelHandler extends SimpleChannelHandler {
        private ConcurrentHashMap<SocketAddress,ByteArrayOutputStream> socket2ByteArrayMap = new ConcurrentHashMap<>();
        
        public ChannelHandler() {
        }

        public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
            channels.add(e.getChannel());
            ChannelBuffer buffer = (ChannelBuffer) e.getMessage();
            logger.info(e.getRemoteAddress().toString());
            
           try {
                SocketAddress curSocketAddress = e.getRemoteAddress();
                ByteArrayOutputStream  baos = socket2ByteArrayMap.get(curSocketAddress);
                if(baos == null){
                    baos = new ByteArrayOutputStream(2000);
                    socket2ByteArrayMap.put(curSocketAddress, baos);
                }
                baos.write(buffer.array());
                
            } catch (IOException ie) {
                Thread.currentThread().interrupt();
            }
        }

        public void exceptionCaught(ChannelHandlerContext context, ExceptionEvent event) {
            logger.error("Error", event.getCause());
            Channel c = context.getChannel();
            c.close().addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    if (future.isSuccess())
                        channels.remove(future.getChannel());
                    else
                        logger.error("FAILED to close channel");
                }
            });
        }

        @Override
        public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
            SocketAddress curSocketAddress = e.getChannel().getRemoteAddress();
            ByteArrayOutputStream  baos =socket2ByteArrayMap.remove(curSocketAddress);
            if(baos != null && baos.size() != 0){
                byte[] receivedBytes = baos.toByteArray();
                receiver.receive(receivedBytes);
            }
            super.channelClosed(ctx, e);
        }

    }

     以上用socket2ByteArrayMap容器维护每个客户端接收到的数据，直至对方关闭为止。 

     很简单吧。。