netty LengthFieldBasedFrameDecoder 使用实例

netty中，通过LengthFieldBasedFrameDecoder 自定义长度解码器解决TCP黏包问题。大多数的协议在协议头中都会携带长度字段，用于标识消息体或则整包消息的长度。LengthFieldBasedFrameDecoder通过指定长度来标识整包消息，这样就可以自动的处理黏包和半包消息，只要传入正确的参数，就可以轻松解决“读半包”的问题。

服务端代码：

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;
}
}

客户端代码：

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 String getData() {
return data;
}

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

完整代码下载：http://download.csdn.net/download/byxdaz/10141694

netty LengthFieldBasedFrameDecoder 使用实例

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