学习netty遇到的关于 LineBasedFrameDecoder 的问题

最近在看《Netty权威指南》这本书，关于TCP粘包/拆包，书中使用的是 LineBasedFrameDecoder 来解决的，但是我在实践的过程中出现了问题，上代码吧。

这个是 server 的代码

package com.cd.netty4.zhc.demo.ex01;

import java.text.SimpleDateFormat;
import java.util.Date;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.util.CharsetUtil;

/** 
 * 本例子参考《Netty权威指南（第2版）》第4章 
 * 先运行 TimeServerExc02，然后运行 TimeClientExc02，可解决 TCP 粘包/拆包问题
 * 使用 LineBasedFrameDecoder + StringDecoder 解决 TCP 粘包/拆包问题
 * */
public class TimeServerExc02 {
    public static void main(String args[]) {
        System.out.println("---------------------- server 测试开始 ---------------------");
        new TimeServerExc02().bind("127.0.0.1", 1234);
        System.out.println("---------------------- server 测试end ---------------------");
    }

    public void bind(String host, int port) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        ServerBootstrap serboot = new ServerBootstrap().group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 1024)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel arg0) throws Exception {
                        arg0.pipeline().addLast(new LineBasedFrameDecoder(1024));
                        arg0.pipeline().addLast("decoder", new StringDecoder());
                        arg0.pipeline().addLast("handler", new TimeServerHandlerExc02());
                    }
                });

        try {
            // 绑定端口，同步等待成功
            ChannelFuture future = serboot.bind(host, port).sync();
            // 等待服务端监听端口关闭
            future.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

class TimeServerHandlerExc02 extends ChannelInboundHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("server channelActive(有client连接上了)..");
        ctx.writeAndFlush(Unpooled.copiedBuffer("您已经成功连接上了 server!", CharsetUtil.UTF_8)); // 必须有flush
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("server channelRead..");
        String msgStr = msg.toString();
        System.out.println("读入client消息:" + msgStr);
        String currentTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
        ByteBuf resp = Unpooled.copiedBuffer(currentTime, CharsetUtil.UTF_8);
        ctx.writeAndFlush(resp);
        System.out.println("向client发送消息:" + currentTime);
    }

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

}

这个是client的代码：

package com.cd.netty4.zhc.demo.ex01;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.util.CharsetUtil;

/** 
 * 本例子参考《Netty权威指南（第2版）》第4.2章 
 * */
public class TimeClientExc02 {

    public static void main(String[] args) {
        try {
            System.out.println("---------------------- client 测试开始 ---------------------");
            new TimeClientExc02().connect("127.0.0.1", 1234);
            System.out.println("---------------------- client 测试end ---------------------");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private int count;

    public void connect(String host, int port) throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap boot = new Bootstrap().group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true).handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                            ch.pipeline().addLast("decoder", new StringDecoder());
                            ch.pipeline().addLast(new TimeClientHandlerExc02());
                        }
                    });
            ChannelFuture future = boot.connect(host, port);
            // 等待客户端链路关闭
            future.channel().closeFuture().sync();
        } finally {
            // 优雅的退出，释放NIO线程组
            group.shutdownGracefully();
        }
    }

    class TimeClientHandlerExc02 extends ChannelInboundHandlerAdapter {

        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            System.out.println("client channelActive(client 连接成功)..");
            for (int i = 0; i < 50; i++) {
                System.out.print(i + ",");
                ctx.writeAndFlush(
                        Unpooled.copiedBuffer("It's a good day , I want to know time--" + i , CharsetUtil.UTF_8)); // 必须有flush
            }
            ctx.flush();
        }

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            System.out.println("client channelRead.." + ++count);
            String msgStr = msg.toString();
            System.out.println("读入 server 消息:" + msgStr);
        }

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

    }

}

我先运行的是server，然后是client，发现 server 的 channelActive(..) 以及 client 的 channelActive(..) 都有运行到，但是后续的 channelRead(..) 方法却迟迟没有运行到，我把 LineBasedFrameDecoder 和 StringDecoder 这两个 解码器去掉，则代码正常，但是会有 TCP 粘包/拆包问题。

在网上查了问题原因，无果，认真看了两遍书，发现 LineBasedFrameDecoder  的工作原理是“ 它依次遍历ByteBuf中的可读字节，判断看是否有‘ ’或者‘ ’，如果有，就在此位置为结束位置，从可读索引到结束位置区间的字节就组成了一行 ”。

所以，我的问题就出在消息结尾处没有加上换行符，修改代码后，可运行。修改后代码如下：

package com.cd.netty4.zhc.demo.ex01;

import java.text.SimpleDateFormat;
import java.util.Date;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.util.CharsetUtil;

/** 
 * 本例子参考《Netty权威指南（第2版）》第4章 
 * 先运行 TimeServerExc02，然后运行 TimeClientExc02，可解决 TCP 粘包/拆包问题
 * 使用 LineBasedFrameDecoder + StringDecoder 解决 TCP 粘包/拆包问题
 * 注意：使用 LineBasedFrameDecoder时，发送的消息结尾一定要是
（官方是 System.getProperty("line.separator")），server端 和 client 都必须如此
 * 因为LineBasedFrameDecoder 的工作原理是，依次遍历Bytebuf中的可读字节，判断是否有“
”或者“
”，如果有则在此位置结束
 * */
public class TimeServerExc02 {
    public static void main(String args[]) {
        System.out.println("---------------------- server 测试开始 ---------------------");
        new TimeServerExc02().bind("127.0.0.1", 1234);
        System.out.println("---------------------- server 测试end ---------------------");
    }

    public void bind(String host, int port) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        ServerBootstrap serboot = new ServerBootstrap().group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 1024)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel arg0) throws Exception {
                        arg0.pipeline().addLast(new LineBasedFrameDecoder(1024));
                        arg0.pipeline().addLast("decoder", new StringDecoder());
                        arg0.pipeline().addLast("handler", new TimeServerHandlerExc02());
                    }
                });

        try {
            // 绑定端口，同步等待成功
            ChannelFuture future = serboot.bind(host, port).sync();
            // 等待服务端监听端口关闭
            future.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

class TimeServerHandlerExc02 extends ChannelInboundHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("server channelActive(有client连接上了)..");
        ctx.writeAndFlush(Unpooled.copiedBuffer("您已经成功连接上了 server!", CharsetUtil.UTF_8)); // 必须有flush
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("server channelRead..");
        String msgStr = msg.toString();
        System.out.println("读入client消息:" + msgStr);
        String currentTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
        ByteBuf resp = Unpooled.copiedBuffer(currentTime + System.getProperty("line.separator"), CharsetUtil.UTF_8);
        ctx.writeAndFlush(resp);
        System.out.println("向client发送消息:" + currentTime);
    }

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

}
package com.cd.netty4.zhc.demo.ex01;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.util.CharsetUtil;

/** 
 * 本例子参考《Netty权威指南（第2版）》第4.2章 
 * 注意：使用 LineBasedFrameDecoder时，发送的消息结尾一定要是
（官方是 System.getProperty("line.separator")），server端 和 client 都必须如此
 * 因为LineBasedFrameDecoder 的工作原理是，依次遍历Bytebuf中的可读字节，判断是否有“
”或者“
”，如果有则在此位置结束
 * */
public class TimeClientExc02 {

    public static void main(String[] args) {
        try {
            System.out.println("---------------------- client 测试开始 ---------------------");
            new TimeClientExc02().connect("127.0.0.1", 1234);
            System.out.println("---------------------- client 测试end ---------------------");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private int count;

    public void connect(String host, int port) throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap boot = new Bootstrap().group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true).handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                            ch.pipeline().addLast("decoder", new StringDecoder());
                            ch.pipeline().addLast(new TimeClientHandlerExc02());
                        }
                    });
            ChannelFuture future = boot.connect(host, port);
            // 等待客户端链路关闭
            future.channel().closeFuture().sync();
        } finally {
            // 优雅的退出，释放NIO线程组
            group.shutdownGracefully();
        }
    }

    class TimeClientHandlerExc02 extends ChannelInboundHandlerAdapter {

        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            System.out.println("client channelActive(client 连接成功)..");
            for (int i = 0; i < 50; i++) {
                System.out.print(i + ",");
                ctx.writeAndFlush(
                        Unpooled.copiedBuffer("It's a good day , I want to know time--" + i + "
", CharsetUtil.UTF_8)); // 必须有flush
            }
            ctx.flush();
        }

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            System.out.println("client channelRead.." + ++count);
            String msgStr = msg.toString();
            System.out.println("读入 server 消息:" + msgStr);
        }

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

    }

}

查看了 LineBasedFrameDecoder 的部分源码，确实是以换行作为分割符的。

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原文地址：https://www.cnblogs.com/klbc/p/10887072.html