Netty LengthFieldBasedFrameDecoder usage example

       In netty, the LengthFieldBasedFrameDecoder custom length decoder is used to solve the problem of TCP sticky packets. Most protocols carry a length field in the protocol header to identify the length of the message body or the entire packet. LengthFieldBasedFrameDecoder identifies the entire packet of messages by specifying the length, so that sticky packets and half-packet messages can be automatically processed. As long as the correct parameters are passed in, the problem of "reading half-packets" can be easily solved.

Server code:

package cc.zychen.com;

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.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class EchoServer {

 public void bind(int port) throws Exception {
  EventLoopGroup bossGroup = new NioEventLoopGroup();
  EventLoopGroup workerGroup = new NioEventLoopGroup();
  try{
  ServerBootstrap b = new ServerBootstrap();
  b.group(bossGroup, workerGroup)
  .channel(NioServerSocketChannel.class)
  .option(ChannelOption.SO_BACKLOG, 100)
  .handler(new LoggingHandler(LogLevel.INFO))
  .childHandler(new ChannelInitializer<SocketChannel>() {

   @Override
   protected void initChannel(SocketChannel ch) throws Exception {
    // TODO Auto-generated method stub
    ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(65535,2,4,0,2));
    ch.pipeline().addLast(new EchoServerHandler());
   }

  });
  
  //bind port
  ChannelFuture f = b.bind(port).sync();
  //wait
  f.channel().closeFuture().sync();
  }finally{
   bossGroup.shutdownGracefully();
   workerGroup.shutdownGracefully();
  }
 }
 /**
  * @param args
  */
 public static void main(String[] args) {
  int port = 8080;
  try {
   if(args != null && args.length > 0){
    port = Integer.parseInt(args[0]);
   }
   new EchoServer().bind(port);
  } catch (Exception e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }

 }

}

package cc.zychen.com;
import java.nio.charset.Charset;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
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 {
 
  ByteBuf body = (ByteBuf)msg;
  if(body.readableBytes() <= 0){
   ctx.fireChannelRead(msg);
  }
  CCMessageHeader recHd = new CCMessageHeader();
  int nLength = body.readInt();
  int nType = body.readInt();
  int nDataSize = body.readableBytes();
  byte [] aa = new byte[nDataSize];
  body.readBytes(aa);
  String myMsg = new String(aa,Charset.forName("utf-8"));
  
  
  System.out.println("this is "+ ++ counter +" times receive client:[" + myMsg +"]" +" Type["+ nType +"]");
 
  CCMessageHeader hd = new CCMessageHeader();
  hd.setType(2);
  hd.setData("server data...");
  ByteBuf echo = Unpooled.directBuffer();
  echo.writeBytes(hd.getMessageFlag());
  echo.writeInt(hd.getLength());
  echo.writeInt(hd.getType());
  echo.writeCharSequence(hd.getData(), Charset.forName("utf-8"));
  ctx.writeAndFlush(echo);
 }

 @Override
 public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
  ctx.flush();
 }

 @Override
 public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
   throws Exception {
  cause.printStackTrace();
  ctx.close();
 }

}

package cc.zychen.com;

public class CCMessageHeader {
 protected byte[] messageFlag = new byte[2];
 protected int length;
 protected int type;
 protected String data;
 
 CCMessageHeader(){
  messageFlag[0] = (byte) 0xaa;
  messageFlag[1] = (byte) 0xbb;
 }
 
 public byte[] getMessageFlag() {
  return messageFlag;
 }
 public void setMessageFlag(byte[] messageFlag) {
  this.messageFlag = messageFlag;
 }
 public int getType() {
  return type;
 }
 public void setType(int type) {
  this.type = type;
 }
 public int getLength() {
  return length;
 }
 public void setLength(int length) {
  this.length = length;
 }

 public String getData() {
  return data;
 }

 public void setData(String data) {
  this.data = data;
  length = data.length() + 4;
 }
}

Client code:

package cc.zychen.com;

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.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class EchoClient {

 public void connect(String ip,int port) throws InterruptedException{
  EventLoopGroup group = new NioEventLoopGroup();
  try{
  Bootstrap b = new Bootstrap();
  b.group(group)
  .option(ChannelOption.TCP_NODELAY, true)
  .channel(NioSocketChannel.class)
  .handler(new ChannelInitializer<SocketChannel>() {

   @Override
   protected void initChannel(SocketChannel ch) throws Exception {
    ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(65535,2,4,0,2));
    ch.pipeline().addLast(new EchoClientHandler());
   }
  });
  
  ChannelFuture f = b.connect(ip, port).sync();
  f.channel().closeFuture().sync();
  } finally{
   group.shutdownGracefully();
  }
 }
 
 /**
  * @param args
  */
 public static void main(String[] args) {
  int port = 8080;
  try {
   if(args != null && args.length > 0){
    port = Integer.parseInt(args[0]);
   }
   new EchoClient().connect("127.0.0.1", port);
  } catch (Exception e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
 }
}

package cc.zychen.com;

import java.nio.charset.Charset;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class EchoClientHandler extends ChannelInboundHandlerAdapter {
 private int counter = 0;
 static final String ECHO_REQ = "Hi,liujunliang. Welcome to Netty.@_";
 @Override
 public void channelRead(ChannelHandlerContext ctx, Object msg)
   throws Exception {
  
  ByteBuf body = (ByteBuf)msg;
  CCMessageHeader recHd = new CCMessageHeader();
  int nLength = body.readInt();
  int nType = body.readInt();
  int nDataSize = body.readableBytes();
  byte [] aa = new byte[nDataSize];
  body.readBytes(aa);
  String myMsg = new String(aa,Charset.forName("utf-8"));
  
  
  System.out.println("this is "+ ++ counter +" times receive server:[" + myMsg +"]" +" Type["+ nType +"]");
 }

 @Override
 public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
   throws Exception {
  cause.printStackTrace();
  ctx.close();
 }

 @Override
 public void channelActive(ChannelHandlerContext ctx) throws Exception {
  CCMessageHeader hd = new CCMessageHeader();
  hd.setType(1);
  for(int n=0; n<10; n++){
   String strData = String.format("client data%d...", n+1);
   hd.setData(strData);
   ByteBuf echo = Unpooled.directBuffer();
   echo.writeBytes(hd.getMessageFlag());
   echo.writeInt(hd.getLength());
   echo.writeInt(hd.getType());
   echo.writeCharSequence(hd.getData(), Charset.forName("utf-8"));
   ctx.write(echo);
  }
  ctx.flush();
 }

 @Override
 public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
  ctx.flush();
 }

}

package cc.zychen.com;

public class CCMessageHeader {
 protected byte[] messageFlag = new byte[2];
 protected int length;
 protected int type;
 protected String data;
 
 CCMessageHeader(){
  messageFlag[0] = (byte) 0xaa;
  messageFlag[1] = (byte) 0xbb;
 }
 
 public byte[] getMessageFlag() {
  return messageFlag;
 }
 public void setMessageFlag(byte[] messageFlag) {
  this.messageFlag = messageFlag;
 }
 public int getType() {
  return type;
 }
 public void setType(int type) {
  this.type = type;
 }
 public int getLength() {
  return length;
 }
 public void setLength(int length) {
  this.length = length;
 }

 public String getData() {
  return data;
 }

 public void setData(String data) {
  this.data = data;
  length = data.length() + 4;
 }
}

Complete code download: http://download.csdn.net/download/byxdaz/10141694