netty 支持socket通信

• 1，netty 大大簡化了socket開發，提高了socket的性能。
• 2，Netty提供異步的、事件驅動的網絡應用程序框架和工具，
  用以快速開發高性能、高可靠性的網絡服務器和客戶端程序。

系列文章

[netty 基本使用- 作為http服務器][gcssloop]
[gcssloop]: http://www.lxweimin.com/p/cd88723c96dc

服務器端代碼

ServerSocket.java

    public class ServerSocket {
    public static void main(String ...arg) throws Exception {

        //負責接收客戶端連接
        NioEventLoopGroup bossGroup = new NioEventLoopGroup();

        //負責處理連接
        NioEventLoopGroup wokerGroup = new NioEventLoopGroup();

        try{

            ServerBootstrap bootstrap = new ServerBootstrap();

            bootstrap.group(bossGroup,wokerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ServerInitializer());

            //綁定端口號
            ChannelFuture channelFuture = bootstrap.bind(9999).sync();
            channelFuture.channel().closeFuture().sync();

        } finally {
            bossGroup.shutdownGracefully();
            wokerGroup.shutdownGracefully();
        }

    }
}

** ServerInitializer.java **

public class ServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
      ChannelPipeline pipeline = ch.pipeline();

      //數據分包，組包，粘包
      pipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,0,4,0,4));
      pipeline.addLast(new LengthFieldPrepender(4));

      pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
      pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));

      pipeline.addLast(new ServerHandler());


    }
}

** ServerHandler.java 處理業務 **

    public class ServerHandler extends SimpleChannelInboundHandler<String> {

        @Override
        protected void channelRead0(ChannelHandlerContext ctx, String msg) throws   Exception {
            //接收到的數據
            System.out.println(ctx.channel().remoteAddress()+" , "+msg);
    
            //返回給客戶端的數據
            ctx.channel().writeAndFlush("server: "+ UUID.randomUUID());
        }
    
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws  Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }

客戶端端代碼

** ClientSocket.java **

    public class ClientSocket {
    public static void main(String[] arg) throws Exception {
        NioEventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class)
                    .handler(new Clientinitializer());

            ChannelFuture channelFuture = bootstrap.connect("localhost", 9999).sync();
            channelFuture.channel().closeFuture().sync();

        } finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

** Clientinitializer.java **

    public class Clientinitializer extends ChannelInitializer<SocketChannel> {

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        //數據分包，組包，粘包
        pipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,0,4,0,4));
        pipeline.addLast(new LengthFieldPrepender(4));

        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));

        pipeline.addLast(new ClientHandler());

    }
}

**ClientHandler.java 處理業務 **

public class ClientHandler extends SimpleChannelInboundHandler<String> {

    //接收服務端數據&發送數據
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {

        System.out.println("客戶端接收到的消息： "+msg);

        ctx.writeAndFlush(LocalDateTime.now());

        //完成通信后關閉連接
        //ctx.close();
    }

    //和服務器建立連接
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
      ctx.writeAndFlush("在嗎?。。?！");
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

** 可以多次和服務器端通信的寫法 **

    public class ClientSocket2 {
    public static void main(String[] arg) throws Exception {
        NioEventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class)
                    .handler(new Clientinitializer());

            ChannelFuture channelFuture = bootstrap.connect("localhost", 9999).sync();
            Channel channel = channelFuture.channel();

            //接收輸入的數據
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in, CharsetUtil.UTF_8));
            while (true) {
                String sendMsg = bufferedReader.readLine() ;
                if ("esc".equals(sendMsg)) {
                    channel.close();
                    break;
                }

                sendMsg += "\r\n";
                channel.writeAndFlush(sendMsg);
            }


        } finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

LengthFieldBasedFrameDecoder

netty 常用的處理大數據分包傳輸問題的解決類。

• maxFrameLength：解碼的幀的最大長度。
• lengthFieldOffset： 長度屬性的起始位（偏移位），包中存放有整個大數據包長度的字節，這段字節的其實位置。
• lengthFieldLength：長度屬性的長度，即存放整個大數據包長度的字節所占的長度。
• lengthAdjustmen：長度調節值，在總長被定義為包含包頭長度時，修正信息長度。
• initialBytesToStrip：跳過的字節數，根據需要我們跳過lengthFieldLength個字節，以便接收端直接接受到不含“長度屬性”的內容。

LengthFieldPrepender 編碼類

編碼類，自動將

+----------------+

| "HELLO, WORLD" |

+----------------+

格式的數據轉換成

+--------+----------------+

• 0x000C | "HELLO, WORLD" |

+--------+----------------+

格式的數據

參考文章

[netty 數據分包、組包、粘包處理機制][123]
[123]: http://blog.163.com/linfenliang@126/blog/static/127857195201210821145721/