Netty提供的TCP数据拆包、粘包解决方案
1.前言
关于TCP的数据拆包、粘包的介绍，我在上一篇文章里面已经有过介绍。
想要了解一下的，请点击这里 Chick Here！
今天我们要讲解的是Netty提供的两种解决方案：
- DelimiterBasedFrameDecoder
- FixedLengthFrameDecoder
2.关于Decoder
先观察下两段代码的不同
（1）使用StringDecoder之前
@Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ????try { ????????ByteBuf in = (ByteBuf) msg; ????????String str = in.toString(CharsetUtil.UTF_8); ????????System.out.println("Client:"+str); ????} finally { ????????ReferenceCountUtil.release(msg); ????} }（2）使用StringDecoder之后
@Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ????try { ????????String str = (String) msg; ????????System.out.println("Client:"+str); ????} finally { ????????ReferenceCountUtil.release(msg); ????} }关于Decoder
decoder：n. 解码器
在我看来，Netty数据的解析方式大概为：
发送过程：Buffer------>数据报------>比特流
接受过程：Buffer<------数据报<------比特流
所以我们接受到的msg是一个ButeBuf
使用了Decoder（这里使用StringDecoder举例）之后：
发送过程：Buffer------>数据报------>比特流
接受过程：String<------Buffer<------数据报<------比特流
相当于ByteBuf按照StringDecoder的解码规则，把msg翻译成为了一个字符串。
如何使用Decoder
（1）实际代码演示：
package com.xm.netty.demo02;import java.net.InetSocketAddress;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.Channel;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.nio.NioServerSocketChannel;import io.netty.handler.codec.string.StringDecoder;public class Server { private final int port; public Server(int port) { ????this.port = port; } public static void main(String[] args) { ????int port = 8989; ????try { ????????new Server(port).start(); ????} catch (InterruptedException e) { ????????// TODO Auto-generated catch block ????????e.printStackTrace(); ????} } private void start() throws InterruptedException { ????EventLoopGroup g1 = new NioEventLoopGroup(); ????EventLoopGroup g2 = new NioEventLoopGroup(); ????try { ????????ServerBootstrap bootstrap = new ServerBootstrap(); ?????????bootstrap ????????????????.group(g1,g2) ????????????????.channel(NioServerSocketChannel.class) ????????????????.localAddress(new InetSocketAddress( port)) ????????????????.childHandler(new ChannelInitializer() { ????????????????????@Override ????????????????????protected void initChannel(Channel ch) throws Exception { ????????????????????????ch.pipeline().addLast(new StringDecoder()); ????????????????????????ch.pipeline().addLast(new ServerHandler()); ????????????????????} ????????????????}); ?????????ChannelFuture future = bootstrap.bind().sync(); ?????????future.channel().closeFuture().sync(); ????} finally { ????????g1.shutdownGracefully().sync(); ????????g2.shutdownGracefully().sync(); ????} }}代码改动：
ch.pipeline().addLast(new StringDecoder());
?? ch.pipeline().addLast(new ServerHandler());
（2）多个Decoder的使用顺序：
从前往后，依次解码
?
假设我们有个通过字符串变化为时间的TimeDecoder：
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new TimeDecoder());
? ch.pipeline().addLast(new ServerHandler());
解析规则为：
3.DelimiterBasedFrameDecoder
关于DelimiterBasedFrameDecoder
其实很简单，就是在一个缓冲区的末尾添加一个结束字符。
在规定了最大长度的缓冲区里，遇到一个特殊字符，就截取一次。
原理类似于String的split（）方法。
代码实现
（1）服务端Server
package com.xm.netty.demo03;import java.net.InetSocketAddress;import io.netty.bootstrap.ServerBootstrap;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.Channel;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.nio.NioServerSocketChannel;import io.netty.handler.codec.DelimiterBasedFrameDecoder;import io.netty.handler.codec.string.StringDecoder;public class Server { private final int port; public Server(int port) { ????this.port = port; } public static void main(String[] args) { ????int port = 8989; ????try { ????????new Server(port).start(); ????} catch (InterruptedException e) { ????????// TODO Auto-generated catch block ????????e.printStackTrace(); ????} } private void start() throws InterruptedException { ????EventLoopGroup g1 = new NioEventLoopGroup(); ????EventLoopGroup g2 = new NioEventLoopGroup(); ????try { ????????ServerBootstrap bootstrap = new ServerBootstrap(); ?????????bootstrap ????????????????.group(g1,g2) ????????????????.channel(NioServerSocketChannel.class) ????????????????.localAddress(new InetSocketAddress( port)) ????????????????.childHandler(new ChannelInitializer() { ????????????????????@Override ????????????????????protected void initChannel(Channel ch) throws Exception { ????????????????????????ByteBuf buf = Unpooled.copiedBuffer("$".getBytes()); ????????????????????????ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,buf)); ????????????????????????ch.pipeline().addLast(new StringDecoder()); ????????????????????????ch.pipeline().addLast(new ServerHandler()); ????????????????????} ????????????????}); ?????????ChannelFuture future = bootstrap.bind().sync(); ?????????future.channel().closeFuture().sync(); ????} finally { ????????g1.shutdownGracefully().sync(); ????????g2.shutdownGracefully().sync(); ????} }}（2）服务端ServerHandler
package com.xm.netty.demo03;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.util.CharsetUtil;public class ServerHandler extends ChannelHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ????String str = (String) msg; ????System.out.println("Server:"+str); ????str = "服务器返回--->"+ str+"$"; ????ctx.writeAndFlush(Unpooled.copiedBuffer(str.getBytes())); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ????cause.printStackTrace(); ????ctx.close(); } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { ????System.out.println(DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now())+"一个客户端连接上服务器！"); }}（3）客户端Client
package com.xm.netty.demo03;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;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.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 Client { private final int port; private final String host; public Client(int port, String host) { ????this.port = port; ????this.host = host; } public static void main(String[] args) { ????String host = "127.0.0.1"; ????int port = 8989; ????try { ????????new Client(port, host).start(); ????} catch (InterruptedException e) { ????????// TODO Auto-generated catch block ????????e.printStackTrace(); ????} } private void start() throws InterruptedException { ????EventLoopGroup group = new NioEventLoopGroup(); ????try { ????????Bootstrap bootstrap = new Bootstrap(); ????????bootstrap ????????????????.group(group) ????????????????.channel(NioSocketChannel.class) ????????????????.remoteAddress(host, port) ????????????????.handler(new ChannelInitializer<SocketChannel>() { ????????????????????@Override ????????????????????protected void initChannel(SocketChannel ch) throws Exception { ????????????????????????ByteBuf buf = Unpooled.copiedBuffer("$".getBytes()); ????????????????????????ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,buf)); ????????????????????????ch.pipeline().addLast(new StringDecoder()); ????????????????????????ch.pipeline().addLast(new ClientHandler()); ????????????????????} ????????????????}); ????????ChannelFuture future = bootstrap.connect().sync(); ????????for(int i=10;i<20;i++) { ????????????String str = DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now()) + "---- " +i+"<<<$"; ????????????future.channel().write(Unpooled.copiedBuffer(str.getBytes())); ????????} ????????future.channel().flush(); ????????//future.channel().writeAndFlush(Unpooled.copiedBuffer("Hello Netty!".getBytes())); ????????future.channel().closeFuture().sync(); ????} finally { ????????group.shutdownGracefully().sync(); ????} }}（4）客户端ClientHandler
package com.xm.netty.demo03;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.util.CharsetUtil;import io.netty.util.ReferenceCountUtil;public class ClientHandler extends ChannelHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ????try { ????????String str = (String) msg; ????????System.out.println("Client:"+str); ????} finally { ????????ReferenceCountUtil.release(msg); ????} } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ????cause.printStackTrace(); ????ctx.close(); } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { ????System.out.println(DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now())+"已连接服务器！"); }}运行结果截图
（1）服务端运行结果：
（2）客户端运行结果：
4.FixedLengthFrameDecoder
关于FixedLengthFrameDecoder
其实很简单，就是对规定的发送的数据进行限制长度，
当符合这个长度的情况下，就可以解析。
假设你发送一个’123456‘，’654321‘
那么解析的状况为’12345‘，’66543‘
代码实现
（1）服务端Server
package com.xm.netty.demo04;import java.net.InetSocketAddress;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.Channel;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.nio.NioServerSocketChannel;import io.netty.handler.codec.FixedLengthFrameDecoder;import io.netty.handler.codec.string.StringDecoder;public class Server { private final int port; public Server(int port) { ????this.port = port; } public static void main(String[] args) { ????int port = 8989; ????try { ????????new Server(port).start(); ????} catch (InterruptedException e) { ????????// TODO Auto-generated catch block ????????e.printStackTrace(); ????} } private void start() throws InterruptedException { ????EventLoopGroup g1 = new NioEventLoopGroup(); ????EventLoopGroup g2 = new NioEventLoopGroup(); ????try { ????????ServerBootstrap bootstrap = new ServerBootstrap(); ?????????bootstrap ????????????????.group(g1,g2) ????????????????.channel(NioServerSocketChannel.class) ????????????????.localAddress(new InetSocketAddress( port)) ????????????????.childHandler(new ChannelInitializer() { ????????????????????@Override ????????????????????protected void initChannel(Channel ch) throws Exception { ????????????????????????ch.pipeline().addLast(new FixedLengthFrameDecoder(5)); ????????????????????????ch.pipeline().addLast(new StringDecoder()); ????????????????????????ch.pipeline().addLast(new ServerHandler()); ????????????????????} ????????????????}); ?????????ChannelFuture future = bootstrap.bind().sync(); ?????????future.channel().closeFuture().sync(); ????} finally { ????????g1.shutdownGracefully().sync(); ????????g2.shutdownGracefully().sync(); ????} }}（2）服务端ServerHandler
package com.xm.netty.demo04;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.util.CharsetUtil;public class ServerHandler extends ChannelHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ????String str = (String) msg; ????System.out.println("Server:"+str); ????ctx.writeAndFlush(Unpooled.copiedBuffer(str.getBytes())); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ????cause.printStackTrace(); ????ctx.close(); } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { ????System.out.println(DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now())+"一个客户端连接上服务器！"); }}（3）客户端Client
package com.xm.netty.demo04;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.bootstrap.Bootstrap;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;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.FixedLengthFrameDecoder;import io.netty.handler.codec.string.StringDecoder;public class Client { private final int port; private final String host; public Client(int port, String host) { ????this.port = port; ????this.host = host; } public static void main(String[] args) { ????String host = "127.0.0.1"; ????int port = 8989; ????try { ????????new Client(port, host).start(); ????} catch (InterruptedException e) { ????????// TODO Auto-generated catch block ????????e.printStackTrace(); ????} } private void start() throws InterruptedException { ????EventLoopGroup group = new NioEventLoopGroup(); ????try { ????????Bootstrap bootstrap = new Bootstrap(); ????????bootstrap ????????????????.group(group) ????????????????.channel(NioSocketChannel.class) ????????????????.remoteAddress(host, port) ????????????????.handler(new ChannelInitializer<SocketChannel>() { ????????????????????@Override ????????????????????protected void initChannel(SocketChannel ch) throws Exception { ????????????????????????ch.pipeline().addLast(new FixedLengthFrameDecoder(5)); ????????????????????????ch.pipeline().addLast(new StringDecoder()); ????????????????????????ch.pipeline().addLast(new ClientHandler()); ????????????????????} ????????????????}); ????????ChannelFuture future = bootstrap.connect().sync(); ????????for(int i=123450;i<123460;i++) { ????????????String str = ""+i; ????????????future.channel().write(Unpooled.copiedBuffer(str.getBytes())); ????????} ????????future.channel().flush(); ????????//future.channel().writeAndFlush(Unpooled.copiedBuffer("Hello Netty!".getBytes())); ????????future.channel().closeFuture().sync(); ????} finally { ????????group.shutdownGracefully().sync(); ????} }}（4）客户端ClientHandler
package com.xm.netty.demo04;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.util.CharsetUtil;import io.netty.util.ReferenceCountUtil;public class ClientHandler extends ChannelHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ????try { ????????String str = (String) msg; ????????System.out.println("Client:"+str); ????} finally { ????????ReferenceCountUtil.release(msg); ????} } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ????cause.printStackTrace(); ????ctx.close(); } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { ????System.out.println(DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now())+"已连接服务器！"); }}运行结果截图
（1）服务端运行结果：
（2）客户端运行结果：
3.Netty的粘包、拆包（二）
原文地址：https://www.cnblogs.com/TimerHotel/p/netty03.html