Netty中LineBasedFrameDecoder解码器使用与分析：解决TCP粘包问题
上一篇文章《Netty中TCP粘包问题代码示例与分析》演示了使用了时间服务器的例子演示了TCP的粘包问题，这里使用LineBasedFrameDecoder就是用来解决这个问题的。
不过需要注意的是，LineBasedFrameDecoder见名知其义，可见其是与行相关的，而在前面演示TCP粘包问题时，作者是有意在发送的消息中都加入了换行符，目的也是为了在后面去讲解LineBasedFrameDecoder的使用，当然也是给出一种简单解决TCP粘包问题的方法，或者是通过一个简单案例来让我们这些学习者有更直观的理解。
代码来自于《Netty权威指南》第4章，不过我依然是做了部分的修改。
服务端代码
TimeServer.java
package cn.xpleaf.netty02;import io.netty.bootstrap.ServerBootstrap;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.LineBasedFrameDecoder;import io.netty.handler.codec.string.StringDecoder;public class TimeServer { ???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 ChildChannelHandler()); ???????????// 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(); ???????} ???} ???private class ChildChannelHandler extends ChannelInitializer<SocketChannel> { ???????@Override ???????protected void initChannel(SocketChannel ch) throws Exception { ???????????// 核心在下面两行，加入了LineBasedFrameDecoder和StringDecoder两个解码器 ???????????// 所以当消息到达我们的业务处理handler即TimerServerHandler，所看到的消息 ???????????// 都是前面两个解码器经过处理之后的结果 ???????????ch.pipeline().addLast(new LineBasedFrameDecoder(1024)); ???????????ch.pipeline().addLast(new StringDecoder()); ???????????ch.pipeline().addLast(new TimeServerHandler()); ???????} ???} ???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 TimeServer().bind(port); ???}}TimeServerHandler.java
package cn.xpleaf.netty02;import java.sql.Date;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 TimeServerHandler 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("The time server receive order : " + body + " ; the counter is : " + ++counter); ???????String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? ????????????????new Date(System.currentTimeMillis()).toString() : "BAD ORDER"; ???????currentTime = currentTime + System.getProperty("line.separator"); ???????ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes()); ???????ctx.write(resp); ???} ???@Override ???public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ???????ctx.flush(); ???} ???@Override ???public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { ???????ctx.close(); ???}}客户端代码
TimeClient.java
package cn.xpleaf.netty02;import io.netty.bootstrap.Bootstrap;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.LineBasedFrameDecoder;import io.netty.handler.codec.string.StringDecoder;public class TimeClient { ???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 { ???????????????????????// 核心在下面两行，加入了LineBasedFrameDecoder和StringDecoder两个解码器 ???????????????????????// 所以当消息到达我们的业务处理handler即TimerServerHandler，所看到的消息 ???????????????????????// 都是前面两个解码器经过处理之后的结果 ???????????????????????ch.pipeline().addLast(new LineBasedFrameDecoder(1024)); ???????????????????????ch.pipeline().addLast(new StringDecoder()); ???????????????????????ch.pipeline().addLast(new TimeClientHandler()); ???????????????????} ???????????????}); ???????????// 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 TimeClient().connect(port, "localhost"); ???}}TimeClientHandler.java
package cn.xpleaf.netty02;import java.util.logging.Logger;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 TimeClientHandler extends ChannelInboundHandlerAdapter { ???private static final Logger logger = Logger.getLogger(TimeServerHandler.class.getName()); ???private int counter; ???private byte[] req; ???public TimeClientHandler() { ???????req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes(); ???} ???@Override ???public void channelActive(ChannelHandlerContext ctx) { ???????ByteBuf message = null; ???????for(int i = 0; i < 100; i++) { ???????????message = Unpooled.buffer(req.length); ???????????message.writeBytes(req); ???????????ctx.writeAndFlush(message); ???????} ???} ???@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("Now is : " + body + " ; the counter is : " + ++counter); ???} ???@Override ???public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ???????logger.warning("Unexpected exception from downstream : "); ???????ctx.close(); ???}}测试
服务端运行结果：
The time server receive order : QUERY TIME ORDER ; the counter is : 1The time server receive order : QUERY TIME ORDER ; the counter is : 2The time server receive order : QUERY TIME ORDER ; the counter is : 3...省略多行...The time server receive order : QUERY TIME ORDER ; the counter is : 98The time server receive order : QUERY TIME ORDER ; the counter is : 99The time server receive order : QUERY TIME ORDER ; the counter is : 100客户端运行结果：
Now is : 2018-02-11 ; the counter is : 1Now is : 2018-02-11 ; the counter is : 2Now is : 2018-02-11 ; the counter is : 3...省略多行...Now is : 2018-02-11 ; the counter is : 98Now is : 2018-02-11 ; the counter is : 99Now is : 2018-02-11 ; the counter is : 100从输出结果可以看出，这确实解决了TCP的粘包问题。
原理分析
下面的分析来自于书本上，这里也贴出来：
Netty中LineBasedFrameDecoder解码器使用与分析：解决TCP粘包问题
原文地址：http://blog.51cto.com/xpleaf/2071083