netty自定义协议demo

以下是一个简单的Netty自定义协议的示例代码，该协议由消息头和消息体组成，消息头包含消息的长度信息，消息体包含具体的消息内容。

1. 定义消息类

public class MyMessage {
    private int length;
    private String content;

    // getter and setter methods
}

2. 编写编解码器

public class MyMessageCodec extends MessageToByteEncoder<MyMessage> {
    @Override
    protected void encode(ChannelHandlerContext ctx, MyMessage msg, ByteBuf out) throws Exception {
        byte[] contentBytes = msg.getContent().getBytes(CharsetUtil.UTF_8);
        out.writeInt(contentBytes.length);
        out.writeBytes(contentBytes);
    }
}

public class MyMessageDecoder extends ByteToMessageDecoder {
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        if (in.readableBytes() < 4) {
            return;
        }
        in.markReaderIndex();
        int length = in.readInt();
        if (in.readableBytes() < length) {
            in.resetReaderIndex();
            return;
        }
        byte[] contentBytes = new byte[length];
        in.readBytes(contentBytes);
        String content = new String(contentBytes, CharsetUtil.UTF_8);
        MyMessage message = new MyMessage();
        message.setLength(length);
        message.setContent(content);
        out.add(message);
    }
}

3. 编写服务端和客户端代码

服务端代码：

public class MyServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast(new MyMessageDecoder());
                            pipeline.addLast(new MyServerHandler());
                            pipeline.addLast(new MyMessageCodec());
                        }
                    })
                    .option(ChannelOption.SO_BACKLOG, 128)
                    .childOption(ChannelOption.SO_KEEPALIVE, true);

            ChannelFuture f = b.bind(8888).sync();
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }
}

public class MyServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        MyMessage message = (MyMessage) msg;
        System.out.println("Server receive message: " + message.getContent());
        message.setContent("Hello, " + message.getContent() + "!");
        ctx.writeAndFlush(message);
    }
}

客户端代码：

public class MyClient {
    public static void main(String[] args) throws Exception {
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(workerGroup)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast(new MyMessageCodec());
                            pipeline.addLast(new MyMessageDecoder());
                            pipeline.addLast(new MyClientHandler());
                        }
                    });

            ChannelFuture f = b.connect("localhost", 8888).sync();
            for (int i = 0; i < 10; i++) {
                MyMessage message = new MyMessage();
                message.setContent("world-" + i);
                f.channel().writeAndFlush(message);
                Thread.sleep(1000);
            }
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }
}

public class MyClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        MyMessage message = (MyMessage) msg;
        System.out.println("Client receive message: " + message.getContent());
    }
}

以上代码演示了如何使用Netty实现自定义协议，其中MyMessageCodec和MyMessageDecoder负责编解码，MyServer和MyServerHandler负责服务端逻辑，MyClient和MyClientHandler负责客户端逻辑。在本示例中，自定义协议包含消息头和消息体，消息头包含消息长度信息，消息体包含具体的消息内容。