1、示例说明

本示例为基于行字符串的回显应用示例，客户端通过标准输入获取行字符串，并将字符串发送到服务端；服务端读取客户端行数据，解码之后将数据回写给客户端，同事服务端实现与客户端的读写心跳检测等；

2、服务端说明

服务端基于netty创建，解码器为LineBasedFrameDecoder和StringDecoder，主要功能是将ByteBuf类型数据解码转换为String类型数据；心跳机制基于IdleStateHandler实现；

2.1、服务端代码示例

SocketEchoServer 源码：

public class SocketEchoServer {
    private static  int PORT = 9999;


    public static void main(String[] args){
        SocketEchoServer.startServer(PORT);
    }





    private static void startServer(int port){
        NioEventLoopGroup bossGroup = new NioEventLoopGroup(1);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap sb = new ServerBootstrap();
            sb.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 256)
                    .childOption(ChannelOption.SO_KEEPALIVE, true)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            socketChannel.pipeline().addLast("lineDecodeHandler", new LineBasedFrameDecoder(1024, false, false))
                                    .addLast("stringDecoder", new StringDecoder())
                                    .addLast("heartBeatHandler", new IdleStateHandler(0,0, 30))
                                    .addLast("echoHandler", new SocketEchoServerHandler());
                        }
                    });
            ChannelFuture cf = sb.bind(PORT).sync();
            System.out.println("---- server bind success on port:" + PORT + " ----");
            cf.channel().closeFuture().sync();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

}

说明:

• 创建服务端Channel的事件处理线程组bossGroup，本处设置线程个数为1个；
• 创建客户端连接Channel的事件处理线程组workerGroup，线程个数为默认（处理器个数的2倍）；
• 创建ServerBootstrap并设置相关参数，设置服务端Channel为NioServerSocketChannel，设置服务端的连接缓存为256，添加子连接的ChannelHandler为LineBasedFrameDecoder、StringDecoder、IdleStateHandler、SocketEchoServerHandler；
• 绑定本地端口9999，并同步等待绑定结果；
• 同步等待服务端监听连接的关闭结果；

2.2、SocketEchoServerHandler示例

SocketEchoServerHandler源码：

public class SocketEchoServerHandler extends ChannelInboundHandlerAdapter {


    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        InetSocketAddress address = (InetSocketAddress)ctx.channel().remoteAddress();
        System.out.println("---- client active: host=" + address.getHostName() + ",port=" + address.getPort() + "----");
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        InetSocketAddress address = (InetSocketAddress)ctx.channel().remoteAddress();
        System.out.println("---- client inactive: host=" + address.getHostName() + ",port=" + address.getPort() + "----");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        if(msg instanceof String){
            String str = (String)msg;
            ctx.writeAndFlush(Unpooled.copiedBuffer(str.getBytes()));
            System.out.println("recv form client:" + str);
            return;
        }
    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if(evt instanceof IdleStateEvent){
            IdleStateEvent event = (IdleStateEvent) evt;
            DateTimeFormatter format = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss");
            String dt = DateTime.now().toString(format);
            switch (event.state()){
                case ALL_IDLE:
                    System.out.println(dt + ":服务端与客户端读写超时！");
                    break;
                case READER_IDLE:
                    System.out.println(dt + ":服务端读超时！");
                    break;
                case WRITER_IDLE:
                    System.out.println(dt + ":服务端写超时！");
                    break;
            }
        }
    }
}

channelRead：读取解码器解码转换后的String对象，将对象回写到对应的客户端；

userEventTriggered：若事件类型为IdleStateEvent表明为心跳检测事件，获取对应事件类型并打印；

3、客户端说明

客户端主要功能为连接服务器，从标准输入中读取行字符串，将行数据发送给服务端，同时接收服务端回写的数据；

3.1、客户端示例

SocketEchoClient源码：

public class SocketEchoClient {
    private static String LOCAL_HOST = "127.0.0.1";
    private static int SERVER_PORT = 9999;

    public static void main(String[] args){
        SocketEchoClient.startClient(SERVER_PORT);
    }

    private static void startClient(int serverPort){
        NioEventLoopGroup group = new NioEventLoopGroup(1);

        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .option(ChannelOption.SO_KEEPALIVE, true)
                    .handler(new ChannelInitializer<NioSocketChannel>() {
                        @Override
                        protected void initChannel(NioSocketChannel nioSocketChannel) throws Exception {
                            nioSocketChannel.pipeline().addLast("lineDecodeHandler", new LineBasedFrameDecoder(1024, false, false))
                                    .addLast("stringDecoder",new StringDecoder())
                                    .addLast("echoClientHandler", new SocketEchoClientHandler());
                        }
                    });
            ChannelFuture cf = b.connect(LOCAL_HOST, SERVER_PORT).sync();
            System.out.println("client connect to server success! host:" + LOCAL_HOST + ":" + SERVER_PORT);
            cf.channel().closeFuture().sync();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            group.shutdownGracefully();
        }
    }
    
}

说明：

• 创建一个线程的EventLoopGroup；
• 设置客户端Channel类型为NioSocketChannel；
• 设置客户端ChannelHandler的为LineBasedFrameDecoder、StringDecoder及SocketEchoClientHandler；
• 同步连接服务器；

3.2、SocketEchoClientHandler示例

SocketEchoClientHandler源码：

public class SocketEchoClientHandler extends ChannelInboundHandlerAdapter{
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        if(msg instanceof String){
            String str = (String)msg;
            System.out.println("recv form server:" + str);
            return;
        }
    }


    @Override
    public void channelActive(final ChannelHandlerContext ctx) throws Exception {
        try {
            new Thread(new Runnable() {
                public void run() {
                    Scanner scanner = new Scanner(System.in);
                    while (scanner.hasNextLine()){
                        String line = scanner.nextLine();
                        if(line.startsWith("##stop")){
                            ctx.close();
                            break;
                        }
                        line += System.getProperty("line.separator");
                        System.out.println(line);
                        ctx.writeAndFlush(Unpooled.copiedBuffer(line.getBytes()));
                    }
                }
            }).start();
        }catch (Exception e){
            e.printStackTrace();
            ctx.close();
        }
    }
}

channelRead：读取服务端回写数据；

channelActive：客户端连接成功后，创建并启动读取标准输入处理的线程，线程中读取行数据并将数据发送给服务端；

4、应用演示示例

以下为服务端及客户端的实例输入输出，序号为时序。

服务端：

服务端.png

客户端：

客户端.png

应用示例源码：https://github.com/zhaozhou11/netty-demo.git

Netty源码愫读：
Netty源码愫读（一）ByteBuf相关源码学习 【https://www.jianshu.com/p/016daa404957】
Netty源码愫读（二）Channel相关源码学习【https://www.jianshu.com/p/02eac974258e】
Netty源码愫读（三）ChannelPipeline、ChannelHandlerContext相关源码学习【https://www.jianshu.com/p/be82d0fcdbcc】
Netty源码愫读（四）ChannelHandler相关源码学习【https://www.jianshu.com/p/6ee0a3b9d73a】
Netty源码愫读（五）EventLoop与EventLoopGroup相关源码学习【https://www.jianshu.com/p/05096995d296】
Netty源码愫读（六）ServerBootstrap相关源码学习【https://www.jianshu.com/p/a71a9a0291f3】

Netty应用实战：