Netty中定长解码器的使用
有了前面的基础，定长解码器的使用相对就比较简单了，所以这里只使用服务端的代码，测试时，用telnet作为客户客户端，数据只作单向的发送，即从客户端到服务端。
服务端
EchoServer.java
package cn.xpleaf.netty02;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.FixedLengthFrameDecoder;import io.netty.handler.codec.string.StringDecoder;public class EchoServer { ???public void bind(int port) throws Exception { ???????// 配置服务端的NIO线程组 ???????EventLoopGroup bossGroup = new NioEventLoopGroup(); ???????EventLoopGroup workerGroup = new NioEventLoopGroup(); ???????try { ???????????ServerBootstrap b = new ServerBootstrap(); ???????????b.group(bossGroup, workerGroup) ???????????????.channel(NioServerSocketChannel.class) ???????????????.option(ChannelOption.SO_BACKLOG, 1024) ???????????????.childHandler(new ChannelInitializer<SocketChannel>() { ???????????????????@Override ???????????????????protected void initChannel(SocketChannel ch) throws Exception { ???????????????????????// 添加定长分隔符解码器到pipeline中，长度设置为20 ???????????????????????ch.pipeline().addLast(new FixedLengthFrameDecoder(20)); ???????????????????????// 添加StringDecoder解码器，将ByteBuf解码成字符串对象 ???????????????????????ch.pipeline().addLast(new StringDecoder()); ???????????????????????// 添加业务处理handler ???????????????????????ch.pipeline().addLast(new EchoServerHandler()); ???????????????????} ???????????????}); ???????????// 绑定端口，同步等待成功 ???????????ChannelFuture f = b.bind(port).sync(); ???????????// 等待服务端监听端口关闭 ???????????f.channel().closeFuture().sync(); ???????} finally { ???????????// 优雅退出，释放线程池资源 ???????????bossGroup.shutdownGracefully(); ???????????workerGroup.shutdownGracefully(); ???????} ???} ???public static void main(String[] args) throws Exception { ???????int port = 8080; ???????if(args != null && args.length > 0) { ???????????try { ???????????????port = Integer.valueOf(port); ???????????} catch (NumberFormatException e) { ???????????????// TODO: handle exception ???????????} ???????} ???????new EchoServer().bind(port); ???}}EchoServerHandler.java
package cn.xpleaf.netty02;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;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 { ???????String body = (String) msg; ???????System.out.println("Receive client : [" + body + "]"); ???} ???@Override ???public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ???????ctx.flush(); ???} ???@Override ???public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { ???????// 发生异常，关闭链路 ???????ctx.close(); ???}}测试
启动服务端，在telnet客户端中输入相应字符串：
yeyonghao@yeyonghaodeMacBook-Pro:~$ telnet localhost 8080Trying ::1...Connected to localhost.Escape character is ‘^]‘.Ye Yonghao welcome to Beijing此时查看服务端的输出：
Receive client : [Ye Yonghao welcome t]可以看到中括号时字符数刚好是20个，因为在pipeline中设置定长解码器时，设置的长度就是20。
可以尝试再发送消息：
yeyonghao@yeyonghaodeMacBook-Pro:~$ telnet localhost 8080Trying ::1...Connected to localhost.Escape character is ‘^]‘.Ye Yonghao welcome to BeijingI love you so much!再查看服务端的输出：
Receive client : [Ye Yonghao welcome t]Receive client : [o BeijingI love yo]可以看到服务端把上一次的消息作为这次消息的开始，包括换行符，这说明定长解码器确实是有效果了。
Netty中定长解码器的使用
原文地址：http://blog.51cto.com/xpleaf/2071241