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.]Netty中分隔符解码器代码示例与分析
原文地址：http://blog.51cto.com/xpleaf/2071237