netty学习之路三，定长方式处理拆包黏包问题

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/jjkang_/article/details/88424710

netty除了提供特殊字符拆包之外，还提供了一种定长方式处理拆包的方法。但是，这种方法每次发送的消息必须是固定长度的，如果长度不够，就会阻塞。所以，和特殊字符拆包相比，定长方式处理拆包，优势不大。

server

public class Server {
    public static void main(String[] args) throws Exception{

        EventLoopGroup bossGroup = new NioEventLoopGroup(); // 负责处理来自客户端的链接
        EventLoopGroup workerGroup = new NioEventLoopGroup();//负责处理任务

        ServerBootstrap bootstrap = new ServerBootstrap();//配置类
        bootstrap.group(bossGroup,workerGroup)
                .channel(NioServerSocketChannel.class)
                .option(ChannelOption.SO_SNDBUF, 32*1024)
                .option(ChannelOption.SO_RCVBUF, 32*1024)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        //ByteBuf buf = Unpooled.copiedBuffer("$$".getBytes());
                        //socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, buf));
                        socketChannel.pipeline().addLast(new FixedLengthFrameDecoder(5));
                        socketChannel.pipeline().addLast(new StringDecoder());
                        socketChannel.pipeline().addLast(new StringEncoder());
                        socketChannel.pipeline().addLast(new ServerHandler());//添加处理器
                    }
                })
                .option(ChannelOption.SO_BACKLOG, 128)
                .childOption(ChannelOption.SO_KEEPALIVE, true);

        ChannelFuture future = bootstrap.bind(8888).sync();
        future.channel().closeFuture().sync();//阻塞线程

        workerGroup.shutdownGracefully();
        bossGroup.shutdownGracefully();

    }
}

ServerHandler

public class ServerHandler extends ChannelHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("channelActive is invoked");
    }

    /**
     * 收到数据时调用
     * @param ctx
     * @param msg
     * @throws Exception
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        try{
            System.out.println("server channelRead");
            String result = (String)msg;
            result += "$$";
            System.out.println(result);
            ctx.writeAndFlush(result);//.addListener(ChannelFutureListener.CLOSE);
        }finally {
            ReferenceCountUtil.release(msg);
        }
    }

    /**
     * 抛出异常时调用
     * @param ctx
     * @param cause
     * @throws Exception
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

Client

public class Client {
    public static void main(String[] args) throws Exception{
        EventLoopGroup workerGroup = new NioEventLoopGroup();//负责处理任务

        Bootstrap bootstrap = new Bootstrap();
        bootstrap.group(workerGroup)
                .channel(NioSocketChannel.class)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        //ByteBuf buf = Unpooled.copiedBuffer("$$".getBytes());
                        //socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, buf));
                        socketChannel.pipeline().addLast(new FixedLengthFrameDecoder(5));
                        socketChannel.pipeline().addLast(new StringDecoder());
                        socketChannel.pipeline().addLast(new StringEncoder());
                        socketChannel.pipeline().addLast(new ClientHandler());
                    }
                })
                .option(ChannelOption.SO_BACKLOG, 128)
                .option(ChannelOption.SO_KEEPALIVE, true);

        ChannelFuture f = bootstrap.connect("127.0.0.1",8888).sync();
        f.channel().writeAndFlush("7777");
        f.channel().writeAndFlush("ddd$$");


        f.channel().closeFuture().sync();
        workerGroup.shutdownGracefully();

    }

ClientHandler

public class ClientHandler extends ChannelHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client channelActive");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        try {
            System.out.println("client channelRead");
            //String response = (String)msg;
            System.out.println("收到的响应为:"+msg);
        }finally {
            ReferenceCountUtil.release(msg);
        }
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client channelReadComplete");
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client channelInactive");
    }

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

}