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‘