网络编程复习（八）：Netty解决拆包粘包问题--定长方式

这里说道定长方式，个人觉得定长这种定义方式还是不够方便，因为当数据没有达到规定的长度的时候，你就必须用空格（或其他字符）补齐长度，否则这段不够的数据将会丢失。

在Netty中，分隔符与定长唯一的实现区别就是DelimiterBasedFrameDecoder（自定义分隔符）改为了FixedLengthFrameDecoder定长类。

注意：使用定长类，会有中文乱码问题，这里就要说说Netty的编解码技术了，下一章会说，同时除了这两种方式，还有第三张就是自定义传输协议，分为消息头和消息体，消息头会定义消息体的长度，这样就可以知道数据有多长，同样可以解决拆包粘包问题。

关于自定义协议可以看这篇文章，这里我就不说了
http://blog.csdn.net/zbw18297786698/article/details/53691915
client：

package 网络编程_netty2;

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

public class client {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup worker = new NioEventLoopGroup();
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(worker)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
//ByteBuf buf = Unpooled.copiedBuffer("$_".getBytes());
//ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, buf));//自定义分隔符
ch.pipeline().addLast(new FixedLengthFrameDecoder(5));
ch.pipeline().addLast(new StringDecoder());//设置字符串形式的解码
ch.pipeline().addLast(new ClientHandler());
}
});
ChannelFuture f = bootstrap.connect("127.0.0.1", 8888).sync();
f.channel().writeAndFlush(Unpooled.wrappedBuffer("aaaaabbbbbb".getBytes()));
f.channel().writeAndFlush(Unpooled.wrappedBuffer("bbbb".getBytes()));
f.channel().writeAndFlush(Unpooled.wrappedBuffer("ccccccc".getBytes()));
f.channel().closeFuture().sync();
worker.shutdownGracefully();
}

}

serverhandler类和clientHandler类与上一章一样，这里就不复制了。

server：

package 网络编程_netty2;

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

public class Server {
private int port;

public Server(int port){
this.port = port;
}
public void run()throws Exception{
EventLoopGroup boss = new NioEventLoopGroup();
EventLoopGroup workers = new NioEventLoopGroup();
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(boss, workers)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
//ByteBuf buf = Unpooled.copiedBuffer("$_".getBytes());
//ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, buf));
ch.pipeline().addLast(new FixedLengthFrameDecoder(5));
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new ServerHandler());
}
});
ChannelFuture f = bootstrap.bind(port).sync();
f.channel().closeFuture().sync();
workers.shutdownGracefully();
boss.shutdownGracefully();
}
public static void main(String[] args) throws Exception {
new Server(8888).run();
}
}

注意：我client端发送的数据是不够长度的，因此会造成数据丢失，用空格补全就可以了，这里就不贴了，下面看下输出内容：

client端：

hello
hello
hello
hello

server端：

aaaaa
bbbbb
bbbbb
ccccc