FixedLengthFrameDecoder使用

FixedLengthFrameDecoder是netty提供的固定长度解码器，它能够按照指定的长度对消息进行解码，开发者不需要考虑TCP的粘包拆包问题，非常使用。下面通过一个实例来具体了解一下：

1、服务端:
在服务端的ChannelPipeline中新增FixedLengthFrameDecoder，消息截取长度自定义。

public class EchoServer {

public void bind(int port) throws InterruptedException {

    EventLoopGroup bossGroup = new NioEventLoopGroup();

    EventLoopGroup workerGroup = new NioEventLoopGroup();

    try {

        ServerBootstrap boot = new ServerBootstrap();

        boot.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
                .option(ChannelOption.SO_BACKLOG, 100).childHandler(new ChannelInitializer<SocketChannel>() {

                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(new FixedLengthFrameDecoder(7));
                        ch.pipeline().addLast(new StringDecoder());
                        ch.pipeline().addLast(new EchoServerHandler());
                    }
                });

        // 绑定端口，同步等待成功
        ChannelFuture cf = boot.bind(port).sync();
        // 等待服务器监听端口关闭
        cf.channel().closeFuture().sync();
    } finally {
        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();
    }
}

public static void main(String[] args) {
    int port = 8080;
    try {
        new EchoServer().bind(port);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}
}

服务端handler

public class EchoServerHandler extends ChannelHandlerAdapter {

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

@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

    System.out.println("Receive client : [" + msg + "]");

}

}

2、客户端

public class EchoClient {

public void connect(int port, String host) throws InterruptedException {

    EventLoopGroup group = new NioEventLoopGroup();

    try {
        Bootstrap boot = new Bootstrap();

        boot.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true);

        boot.handler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
                ch.pipeline().addLast(new EchoClientHandler());
            }

        });

        ChannelFuture cf = boot.connect(host, port).sync();
        cf.channel().closeFuture().sync();

    } finally {
        group.shutdownGracefully();
    }
}

public static void main(String[] args) throws InterruptedException {
    new EchoClient().connect(8080, "127.0.0.1");
}

}

客户端handler
public class EchoClientHandler extends ChannelHandlerAdapter {

public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
    super.channelRead(ctx, msg);
}

public void channelActive(ChannelHandlerContext ctx) throws Exception {

    ByteBuf out = Unpooled.copiedBuffer("Krisjin  Welcome to Beijing!".getBytes());
    ctx.writeAndFlush(out);

}

}