Netty权威指南之Netty入门程序

package com.hjp.netty.netty;

import io.netty.bootstrap.ServerBootstrap;
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;

public class TimeServer {

    public void bind(int port) throws Exception {
        //配置服务端的线程组，两个线程组，一个用于服务端接收客户端连接，另一个进行SocketChannel的网络读写
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            //ServerBootstrap用于启动NIO服务端的辅助启动类，目的是降低服务端开发复杂度
            ServerBootstrap bootstrap = new ServerBootstrap();
            bootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new ChildChannelHandler());
            //绑定端口，同步等待成功
            ChannelFuture future=bootstrap.bind(port).sync();

            //等待服务端监听端口关闭
            future.channel().closeFuture().sync();
        }finally {
            //优雅退出，释放线程资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    private class ChildChannelHandler extends ChannelInitializer<SocketChannel>{

        protected void initChannel(SocketChannel socketChannel) throws Exception {
            socketChannel.pipeline().addLast(new TimeServerHandler());
        }
    }

    public static void main(String[] args)throws Exception{
        int port=8080;
        if(args!=null&&args.length>0){
            try {
                port=Integer.valueOf(args[0]);
            }catch (NumberFormatException e){

            }
        }
        new TimeServer().bind(port);
    }

}

TimeServer

package com.hjp.netty.netty;

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

import java.util.Date;

public class TimeServerHandler extends ChannelHandlerAdapter {

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

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf byteBuf= (ByteBuf) msg;
        byte[] request=new byte[byteBuf.readableBytes()];
        byteBuf.readBytes(request);
        String body=new String(request,"UTF-8");
        System.out.println("The time server receive order : "+body);
        String currentTime="QUERY TIME ORDER".equalsIgnoreCase(body)?new Date().toString():"BAD ORDER";
        ByteBuf response= Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.write(response);
    }

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

TimeServerHandler

package com.hjp.netty.netty;

import io.netty.bootstrap.Bootstrap;
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;

public class TimeClient {

    public void connect(String host, int port) throws Exception {
        //配置客户端NIO线程组
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            socketChannel.pipeline().addLast(new TimeClientHandler());
                        }
                    });
            //发起异步连接操作，同步等待连接成功
            ChannelFuture future=bootstrap.connect(host,port).sync();

            //等待客户端链路关闭
            future.channel().close().sync();
        }finally {
            //优雅退出，释放NIO线程组
            group.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){

            }
        }
        new TimeClient().connect("127.0.0.1",port);
    }

}

TimeClient

package com.hjp.netty.netty;

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

import java.util.logging.Logger;

public class TimeClientHandler extends ChannelHandlerAdapter {

    private static final Logger logger = Logger.getLogger(TimeClientHandler.class.getName());

    private final ByteBuf firstMessage;

    public TimeClientHandler() {
        byte[] request = "QUERY TIME ORDER".getBytes();
        firstMessage = Unpooled.buffer(request.length);
        firstMessage.writeBytes(request);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        logger.warning("Unexpected exception from downstream : "+cause.getMessage());
        ctx.close();
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(firstMessage);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf byteBuf= (ByteBuf) msg;
        byte[] request=new byte[byteBuf.readableBytes()];
        byteBuf.readBytes(request);
        String body=new String(request,"UTF-8");
        System.out.println("Now is "+body);
    }
}

TimeClientHandler

此程序只是入门程序，存在TCP粘包/拆包问题，需要后期使用解码器

NIO内置编解码类：

LineBasedFrameDecoder是以换行符为结束标志的解码器，从可读索引到结束位置间的字节组成一行；支持携带结束符或者不携带结束符两种解码方式，同时支持配置单行最大长度，如果连续读到最大长度，仍然没有发现换行符，就会抛出异常，同时忽略掉之前读到的异常码流

StringDecoder是将收到的对象转换为字符串

DelimiterBasedFrameDecoder分隔符解码器，可以在构造函数中指定单行最大长度和分隔符，如果达到最大长度还没找到分隔符就会抛出TooLongFrameException异常；该分隔符会过滤掉客户端发来的分隔符

FixedLengthFrameDecoder解码器，无论一次接收到多少数据报，都会按照构造函数中设置的固定长度进行解码，如果是半包消息，FixedLengthFrameDecoder会缓存半包消息并等待下个包到达后进行拼包，直到读取到一个完整的包

其他编解码类：

Google的Protobuf，Facebook的Thrift，JBoss Marshalling，MessagePack