关于netty的多个handler链式模式

1. 老规矩, 引入我们喜闻乐见的maven依赖

 <dependency>
     <groupId>io.netty</groupId>
     <artifactId>netty-all</artifactId>
     <version>4.1.6.Final</version>
 </dependency>

2. 服务端

　　2.1: 服务端引导类:

 public class EchoServer {

     private int port;

     private EchoServer(int port) {
         this.port = port;
     }

     private void start() throws Exception {
         System.out.println("Echo Server Start");
         EventLoopGroup group = new NioEventLoopGroup();
         try {
             ServerBootstrap b = new ServerBootstrap();
             b.group(group)
                     .channel(NioServerSocketChannel.class)
                     .localAddress(new InetSocketAddress(port))
                     .childHandler(new ChannelInitializer<SocketChannel>() {
                         @Override
                         public void initChannel(SocketChannel ch) throws Exception {
                             ch.pipeline().addLast(new EchoOutboundHandler1());
                             ch.pipeline().addLast(new EchoOutboundHandler2());

                             ch.pipeline().addLast(new EchoInboundHandler1());
                             ch.pipeline().addLast(new EchoInboundHandler2());
                         }
                     });
             ChannelFuture f = b.bind().sync();
             System.out.println("Server Start Listen At: " + port);
             f.channel().closeFuture().sync();
         } finally {
             group.shutdownGracefully();
         }
     }

     public static void main(String[] args) throws Exception {
         int port;
         if (args.length > 0) {
             port = Integer.parseInt(args[0]);
         } else {
             port = 8080;
         }
         new EchoServer(port).start();
     }
 }

　　2.2 EchoOutboundHandler1

 public class EchoInboundHandler1 extends ChannelInboundHandlerAdapter {

     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) {
         // 读取msg中的数据
         ByteBuf result = (ByteBuf) msg;
         byte[] bytes = new byte[result.readableBytes()];
         result.readBytes(bytes);
         String resultStr = new String(bytes);
         System.out.println("Server Received: " + resultStr + ": Inbound 1 Is OK");

         // 处理完msg中的数据后往msg中重新存放新的数据继续传递
         result.writeBytes(resultStr.getBytes());
         ctx.fireChannelRead(result);
     }

 }

　　2.3 EchoInboundHandler2

 public class EchoInboundHandler2 extends ChannelInboundHandlerAdapter {

     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) {
         // 读取msg中的数据
         ByteBuf result = (ByteBuf) msg;
         byte[] bytes = new byte[result.readableBytes()];
         result.readBytes(bytes);
         String resultStr = new String(bytes);
         System.out.println("Server Received: " + resultStr + ": Inbound 2 Is OK");

         // 处理完msg中的数据后往msg中重新存放新的数据继续传递
         result.writeBytes(resultStr.getBytes());
         ctx.write(result);
     }

 }

　　2.4 EchoOutboundHandler2

 public class EchoOutboundHandler2 extends ChannelOutboundHandlerAdapter {

     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
         // 读取msg中的数据
         ByteBuf result = (ByteBuf) msg;
         byte[] bytes = new byte[result.readableBytes()];
         result.readBytes(bytes);
         String resultStr = new String(bytes);
         System.out.println("Server Received: " + resultStr + ": Outbound 2 Is OK");

         // 处理完msg中的数据后往msg中重新存放新的数据继续传递
         result.writeBytes(resultStr.getBytes());
         ctx.write(result);
     }
 }

　　2.5 EchoOutboundHandler1

 public class EchoOutboundHandler1 extends ChannelOutboundHandlerAdapter {

     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
         // 读取msg中的数据
         ByteBuf result = (ByteBuf) msg;
         byte[] bytes = new byte[result.readableBytes()];
         result.readBytes(bytes);
         String resultStr = new String(bytes);
         System.out.println("Server Received: " + resultStr + ": Outbound 1 Is OK");

         // 处理完msg中的数据后往msg中重新存放新的数据继续传递
         result.writeBytes(resultStr.getBytes());
         ctx.write(result);
         ctx.flush();
     }
 }

3. 客户端

 public class EchoClient {

     private String host;
     private int port;

     private EchoClient(String host, int port) {
         this.host = host;
         this.port = port;
     }

     private void start() throws Exception {
         System.out.println("Echo Client Start");
         EventLoopGroup group = new NioEventLoopGroup();
         try {
             Bootstrap b = new Bootstrap();
             b.group(group)
                     .channel(NioSocketChannel.class)
                     .remoteAddress(new InetSocketAddress(host, port))
                     .handler(new ChannelInitializer<SocketChannel>() {
                         @Override
                         public void initChannel(SocketChannel ch) throws Exception {
                             ch.pipeline().addLast(new EchoClientHandler());
                         }
                     });
             ChannelFuture f = b.connect().sync();
             System.out.println("Server Client Listen IP: [" + host + ":" + port + "]");
             f.channel().closeFuture().sync();
         } finally {
             group.shutdownGracefully();
         }
     }

     public static void main(String[] args) throws Exception {
         String host = "127.0.0.1";
         int port = 8080;
         int len = 2;
         if (args.length == len) {
             host = args[0];
             port = Integer.parseInt(args[1]);
         }
         new EchoClient(host, port).start();
     }

 }

 public class EchoClientHandler extends ChannelInboundHandlerAdapter {

     @Override
     public void channelActive(ChannelHandlerContext ctx) {
         ctx.writeAndFlush(Unpooled.copiedBuffer("Netty Rocks!", CharsetUtil.UTF_8));
     }

     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) {
         // 读取msg中的数据
         ByteBuf result = (ByteBuf) msg;
         byte[] bytes = new byte[result.readableBytes()];
         result.readBytes(bytes);
         String resultStr = new String(bytes);
         System.out.println("Echo Client Received Is OK: " + resultStr);
         ctx.close();
     }

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

4. 结果:

　　服务端:

　　客户端:

5. 注意事项:

5.1. ChannelInboundHandler之间的传递, 通过调用 ctx.fireChannelRead(msg) 实现; 调用ctx.write(msg) 将传递到ChannelOutboundHandler

5.2. ctx.write()方法执行后, 需要调用flush()方法才能令它立即执行

5.3. ChannelOutboundHandler 在注册的时候需要放在最后一个ChannelInboundHandler之前, 否则将无法传递到ChannelOutboundHandler