netty DelimiterBasedFrameDecoder

netty server

EchoServer

package com.zhaowb.netty.ch5_1;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class EchoServer {

    public void bind(int port) throws Exception {

        // 配置 服务端的 NIO 线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());// 创建分隔符对象 ByteBuf 使用 $_ 作为分隔符。

                            // 第一个参数为单条消息的最大长度，当达到该长度后仍然没有查找到分隔符，就抛出 TooLongFrameException 异常
                            // 防止由于异常码流缺失分隔符导致的内存溢出，这是 netty 解码器的可靠性保护;第二个参数是分隔符缓冲对象。
                            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new EchoServerHandler());
                        }
                    });

            // 绑定端口，同步等待成功。
            ChannelFuture f = b.bind(port).sync();
            // 等待服务端监听端口关闭。
            f.channel().closeFuture().sync();
        } catch (Exception e) {
            // 退出，释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;

        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
            }
        }
        new EchoServer().bind(port);
    }
}

EchoServerHandler

package com.zhaowb.netty.ch5_1;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;

public class EchoServerHandler extends ChannelHandlerAdapter {

    int counter = 0;

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("链接成功！");
    }

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

        // 当读取信息时，先经过 DelimiterBasedFrameDecoder 去掉结束分隔符，然后再使用 StringDecoder 将 ByteBuf 解码成字符串/
        // 然后 EchoServerHandler 收到的数据就是解码后的字符串对象

        String body = (String) msg;
        System.out.println("This is " + ++counter + " times receive client : [" + body + "]");
        body += "$_"; // 由于 设置 DelimiterBasedFrameDecoder 过滤掉了分隔符，返回给客户端时需要在消息的尾部拼接 "$_"

        ByteBuf echo = Unpooled.copiedBuffer(body.getBytes());
        ctx.writeAndFlush(echo);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();// 发生异常，关闭链路
    }
}

netty client

EchoClient

package com.zhaowb.netty.ch5_1;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class EchoClient {

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

        //配置客户端 NIO 线程组
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());// 创建分隔符对象 ByteBuf 使用 $_ 作为分隔符。
                            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new EchoClientHandler());
                        }
                    });
            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();
            // 等待客户端链路关闭
            f.channel().closeFuture().sync();
        } finally {
            // 释放 NIO 线程组
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
            }
        }
        new EchoClient().connect(port, "127.0.0.1");
    }
}

EchoClientHandler

package com.zhaowb.netty.ch5_1;

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;

public class EchoClientHandler extends ChannelHandlerAdapter {

    private int counter;

    static final String ECHO_REQ = "hello.$_";

    public EchoClientHandler() {
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("链接成功！");
        for (int i = 0; i < 10; i++) {
            ctx.writeAndFlush(Unpooled.copiedBuffer(ECHO_REQ.getBytes()));
        }
    }

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

        System.out.println("This is " + ++counter + "times receive server : [" + msg.toString() + "]");
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

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

如果sever 没有 ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));，在接受数据的时候会一起接收到客户端发送的所有数据，造成粘包问题。如果要使用ch.pipeline().addLast(new FixedLengthFrameDecoder(20));就是截取固定长度的信息，超过的不会输出。

https://gitee.com/JiShiMoWang_admin/netty-learning

https://github.com/zhaowenbo1234/netty