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Netty中分隔符解码器代码示例与分析

通过特别解码器的使用,可以解决Netty中TCP的粘包问题,上一篇《Netty中LineBasedFrameDecoder解码器使用与分析:解决TCP粘包问题》通过行解码器的使用来解决TCP粘包问题,这意味着Netty的服务端和客户端在每次发送请求消息前,都需要在消息的尾部拼接换行符。

除了使用行解码器外,Netty还提供了通用的分隔符解码器,即可以自定义消息的分隔符,那就是DelimiterBasedFrameDecoder分隔符解码器。

下面的示例代码来自于《Netty权威指南》第5章,这个例子模拟的是echo服务,即类似于ping,客户端向服务端echo一个消息,服务端就会进行回应。

仍然需要注意的是,代码做了部分修改,也加入了个人的一些注释和分析。

服务端

EchoServer.java

package cn.xpleaf.netty;

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;

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)
                .childHandler(new ChannelInitializer<SocketChannel>() {

                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        // 构建DelimiterBasedFrameDecoder解码器的分隔符
                        ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());
                        // 添加DelimiterBasedFrameDecoder解码器到pipeline中
                        // 1024表示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TooLongFrameExceptio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
                        // 第二个参数就是分隔符缓冲对象
                        ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                        // 添加StringDecoder解码器,将ByteBuf解码成字符串对象
                        ch.pipeline().addLast(new StringDecoder());
                        // 添加业务处理handler
                        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();
        } finally {
            // 优雅退出,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(port);
            } catch (NumberFormatException e) {
                // TODO: handle exception
            }
        }
        new EchoServer().bind(port);
    }
}

EchoServerHandler.java

package cn.xpleaf.netty;

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

public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    private int counter = 0;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body = (String) msg;
        // counter的作用是标记这是第几次收到客户端的请求
        System.out.println("This is : " + ++counter + " times receive client : [" + body + "]");
        // 由于设置DelimiterBasedFrameDecoder过滤掉了分隔符,
        // 所以返回给客户端时需要在请求消息尾部拼接分隔符"$_"
        body += "$_";
        ByteBuf echo = Unpooled.copiedBuffer(body.getBytes());
        ctx.write(echo);
    }

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

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

客户端

EchoClient.java

package cn.xpleaf.netty;

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;

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 {
                        // 构建DelimiterBasedFrameDecoder解码器的分隔符
                        ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());
                        // 添加DelimiterBasedFrameDecoder解码器到pipeline中
                        // 1024表示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TooLongFrameExceptio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
                        // 第二个参数就是分隔符缓冲对象
                        ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                        // 添加StringDecoder解码器,将ByteBuf解码成字符串对象
                        ch.pipeline().addLast(new StringDecoder());
                        // 添加业务处理handler
                        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 {
            // 优雅退出,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(port);
            } catch (NumberFormatException e) {
                // 采用默认值
            }
        }
        new EchoClient().connect(port, "localhost");
    }
}

EchoClientHandler.java

package cn.xpleaf.netty;

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

public class EchoClientHandler extends ChannelInboundHandlerAdapter {

    private int counter;

    static final String ECHO_REQ = "Hi, xpleaf. Welcome to Netty.$_";

    public EchoClientHandler() {

    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        // 构建ByteBuf对象
         ByteBuf req = Unpooled.copiedBuffer(ECHO_REQ.getBytes());
        // 每次调用ctx.write()写入ByteBuf对象时,必须要重新构建一个ByteBuf对象
        // 即不能对一个ByteBuf对象多次使用ctx.write(),否则会发生异常

        // 向服务端发送10次请求
        for(int i = 0; i < 10; i++) {
            ctx.writeAndFlush(Unpooled.copiedBuffer(ECHO_REQ.getBytes()));
            // ctx.writeAndFlush(req);
        }
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body = (String) msg;
        // counter的作用是标记这是第几次收到服务端的回应
        System.out.println("This is : " + ++counter + " times receive server : [" + body + "]");
    }

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

}

测试

服务端输出:

This is : 1 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 2 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 3 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 4 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 5 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 6 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 7 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 8 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 9 times receive client : [Hi, xpleaf. Welcome to Netty.]
This is : 10 times receive client : [Hi, xpleaf. Welcome to Netty.]

客户端输出:

This is : 1 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 2 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 3 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 4 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 5 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 6 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 7 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 8 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 9 times receive server : [Hi, xpleaf. Welcome to Netty.]
This is : 10 times receive server : [Hi, xpleaf. Welcome to Netty.]