netty5 LengthFieldBasedFrameDecoder实例（解决半包）

1,使用LengthFieldPrepender编码，LengthFieldBasedFrameDecoder解码的netty传输

可以解决半包粘包

2 代码部分

tcpserver

package com.bimatrix.revit.nettyTest;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
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.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;

import org.apache.log4j.Logger;
  
public class TcpServer {  
  
    private static final Logger logger = Logger.getLogger(TcpServer.class);  
    private static final String IP = "127.0.0.1";  
    private static final int PORT = 9999;  
    /**用于分配处理业务线程的线程组个数 */  
    protected static final int BIZGROUPSIZE = Runtime.getRuntime().availableProcessors()*2; //默认  
    /** 业务出现线程大小*/  
    protected static final int BIZTHREADSIZE = 4;  
        /* 
     * NioEventLoopGroup实际上就是个线程池, 
     * NioEventLoopGroup在后台启动了n个NioEventLoop来处理Channel事件, 
     * 每一个NioEventLoop负责处理m个Channel, 
     * NioEventLoopGroup从NioEventLoop数组里挨个取出NioEventLoop来处理Channel 
     */  
    private static final EventLoopGroup bossGroup = new NioEventLoopGroup(BIZGROUPSIZE);  
    private static final EventLoopGroup workerGroup = new NioEventLoopGroup(BIZTHREADSIZE);  
      
    protected static void run() throws Exception {  
        ServerBootstrap b = new ServerBootstrap();  
        b.group(bossGroup, workerGroup);  
        b.channel(NioServerSocketChannel.class);  
        b.childHandler(new ChannelInitializer() {  
            @Override  
            public void initChannel(SocketChannel ch) throws Exception {  
                ChannelPipeline pipeline = ch.pipeline();  
                pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));  
                pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));  
                pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8));  
                pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8));  
                pipeline.addLast(new TcpServerHandler());  
            }  
        });  
  
        // b.bind(IP, PORT).sync();  
    	ChannelFuture f = b.bind(PORT).sync(); // (7)


		f.channel().closeFuture().sync();
        
        
        logger.info("TCP服务器已启动");  
    }  
      
    protected static void shutdown() {  
        workerGroup.shutdownGracefully();  
        bossGroup.shutdownGracefully();  
    }  
  
    public static void main(String[] args) throws Exception {  
        logger.info("开始启动TCP服务器...");  
        TcpServer.run();  
//      TcpServer.shutdown();  
    }  
}  

TcpServerHandler

package com.bimatrix.revit.nettyTest;



import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
  
public class TcpServerHandler extends ChannelHandlerAdapter  {  
  
	@Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) { // (2)
	   ctx.write(msg); // (1)
       String obj= (String)msg;
       System.out.println("访问数据"+obj);
      // ctx.write(obj); // (1)
       ctx.flush(); // (2)

    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { // (4)

       // Close theconnection when an exception is raised.
       cause.printStackTrace();
       ctx.close();
    }
    @Override
    public void channelActive(final ChannelHandlerContext ctx) {
            ctx.writeAndFlush("有客户端连接"); // (3)
    }
  
}  

TcpClientHander

package com.bimatrix.revit.nettyTest;

import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;

public class TcpClientHandler extends ChannelHandlerAdapter {  
    public TcpClientHandler() {  
    }  
    //private byte[] req;
    /** 
     * 链路链接成功 
     */  
    @Override  
    public void channelActive(ChannelHandlerContext ctx) throws Exception {  
	    /*for (int i = 0; i < 1000; i++) {
	        ctx.writeAndFlush("1ac");
	    } */
        // 链接成功后发送  
    }  
  
    @Override  
    public void channelRead(ChannelHandlerContext ctx, Object msg)  
            throws Exception {  
    	 System.out.println("client收到数据" +msg);
//    	 ctx.write("收到数据!"); 
//    	 ctx.write(msg); 
//    	 ctx.write("w2d"); 
  
    }  
  
    @Override  
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {  
        ctx.flush();  
    }  
  
    @Override  
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)  
            throws Exception {  
        cause.printStackTrace();  
        ctx.close();  
    }  
}  

TcpClient

package com.bimatrix.revit.nettyTest;

import io.netty.bootstrap.Bootstrap;  
import io.netty.channel.Channel;  
import io.netty.channel.ChannelInitializer;  
import io.netty.channel.ChannelOption;  
import io.netty.channel.ChannelPipeline;  
import io.netty.channel.EventLoopGroup;  
import io.netty.channel.nio.NioEventLoopGroup;  
import io.netty.channel.socket.nio.NioSocketChannel;  
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;  
import io.netty.handler.codec.LengthFieldPrepender;  
import io.netty.handler.codec.string.StringDecoder;  
import io.netty.handler.codec.string.StringEncoder;  
import io.netty.util.CharsetUtil;  
  
import org.apache.log4j.Logger;  
  
public class TcpClient {  
    private static final Logger logger = Logger.getLogger(TcpClient.class);  
    public static String HOST = "127.0.0.1";  
    public static int PORT = 9999;  
      
    public static Bootstrap bootstrap = getBootstrap();  
    public static Channel channel = getChannel(HOST,PORT);  
    /** 
     * 初始化Bootstrap 
     * @return 
     */  
    public static final Bootstrap getBootstrap(){  
        EventLoopGroup group = new NioEventLoopGroup();  
        Bootstrap b = new Bootstrap();  
        b.group(group).channel(NioSocketChannel.class);  
        b.handler(new ChannelInitializer() {  
            @Override  
            protected void initChannel(Channel ch) throws Exception {  
                ChannelPipeline pipeline = ch.pipeline();  
                pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));  
                pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));  
                pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8));  
                pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8));  
                pipeline.addLast("handler", new TcpClientHandler());  
            }  
        });  
        b.option(ChannelOption.SO_KEEPALIVE, true);  
        return b;  
    }  
  
    public static final Channel getChannel(String host,int port){  
        Channel channel = null;  
        try {  
            channel = bootstrap.connect(host, port).sync().channel();  
        } catch (Exception e) {  
            logger.error(String.format("连接Server(IP[%s],PORT[%s])失败", host,port),e);  
            return null;  
        }  
        return channel;  
    }  
  
    public static void sendMsg(String msg) throws Exception {  
        if(channel!=null){  
            channel.writeAndFlush(msg).sync();  
        }else{  
            logger.warn("消息发送失败,连接尚未建立!");  
        }  
    }  
  
    public static void main(String[] args) throws Exception {
 
        try {  
            long t0 = System.nanoTime();  
            for (int i = 0; i < 100000; i++) { 
            	if(i%3==0){
            		 TcpClient.sendMsg(i+"11aaa222aaa"); 
            	}else if(i%3==1){
            		 TcpClient.sendMsg(i+"222cccdddbbbbbbbbbbbb"); 
            	}else if(i%3==2){
           		 TcpClient.sendMsg(i+"333cccddda12ccccccccccccccccccccccccc"); 
            	}
            }  
            long t1 = System.nanoTime();  
            System.out.println((t1-t0)/1000000.0);  
        } catch (Exception e) {  
            e.printStackTrace();  
        }  
    }  
}  

ps :看到楼下评论有提到对于tcp clietn类的连接server在哪没找到：

连接在这里

 public static Channel channel = getChannel(HOST,PORT);  

初始化一个静态变量 写的有点略不好理解

可以参考以下 https://blog.csdn.net/lihongye_10/article/details/16844543

由于静态变量是通过赋值操作进行初始化的，因此可以通过静态函数返回值的方式为其初始化。如：

public class Test {
    public static int _i = init();

    private static int init() {
        return 10;
    }
}

其本质与下面的代码相同：

public class Test {
    public static int _i;
    static {
        _i = init();
    }

    private static int init() {
        return 10;
    }
}

上面代码部分下面这一块 主要测试消息发送是否会造成粘包
 for (int i = 0; i < 100000; i++) { 
            if(i%3==0){
            TcpClient.sendMsg(i+"11aaa222aaa"); 
            }else if(i%3==1){
            TcpClient.sendMsg(i+"222cccdddbbbbbbbbbbbb"); 
            }else if(i%3==2){
            TcpClient.sendMsg(i+"333cccddda12ccccccccccccccccccccccccc"); 
            }
            }