java网络通信：netty

Netty提供异步的、事件驱动的网络应用程序框架和工具，用以快速开发高性能、高可靠性的网络服务器和客户端程序。

也就是说，Netty 是一个基于NIO的客户，服务器端编程框架，使用Netty 可以确保你快速和简单的开发出一个网络应用，例如实现了某种协议的客户，服务端应用。Netty相当简化和流线化了网络应用的编程开发过程，例如，TCP和UDP的socket服务开发。

本文示例采用netty 5.0。上代码.

服务端:

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class TimeServer {

    public void bind(int port) throws Exception {
        // 配置服务端的NIO，循环事件线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();//配置类
            //NioServerSocketChannel作为channel类，它的功能对应于JDK NIO类库中的ServerSocketChannel
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new TimeServerHandler());//绑定事件处理类
            // 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(args[0]);
            } catch (NumberFormatException e) {
                // 采用默认值
            }
        }
        new TimeServer().bind(port);
    }
}

服务端事务处理类:

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

public class TimeServerHandler extends ChannelHandlerAdapter {
　　/*当有数据时，自动调用，读取msg*/
    public void channelRead(ChannelHandlerContext ctx, Object msg)
        throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body = new String(req, "UTF-8");
        System.out.println("The time server receive order : " + body);
        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new java.util.Date(
                System.currentTimeMillis()).toString() : "BAD ORDER";
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.write(resp);
    }
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
    ctx.close();
    }
}

客户端：

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(int port, String host) throws Exception {
        // 配置客户端NIO线程组
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
//ChannelInitializer<SocketChannel>匿名类初始化channel的pipeline，将客户端事务处理类加入到队列中
                        @Override
                        public void initChannel(SocketChannel ch)
                                throws Exception {
                            ch.pipeline().addLast(new TimeClientHandler());
                        }
                    });
            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();

            // 当代客户端链路关闭
            f.channel().closeFuture().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(args[0]);
        } catch (NumberFormatException e) {
        // 采用默认值
        }
    }
    new TimeClient().connect(port, "127.0.0.1");
    }
}

客户端事件处理类：

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[] req = "QUERY TIME ORDER".getBytes();
        firstMessage = Unpooled.buffer(req.length);
        firstMessage.writeBytes(req);
    }
　　/*连接成功后，自动发送消息*/
    public void channelActive(ChannelHandlerContext ctx) {
    　　ctx.writeAndFlush(firstMessage);
    }
　　/*有消息返回时，自动调用该函数读取*/
    public void channelRead(ChannelHandlerContext ctx, Object msg)
        throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body = new String(req, "UTF-8");
        System.out.println("Now is : " + body);
    }
　　/*发生异常时，自动调用*/
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // 释放资源
        logger.warning("Unexpected exception from downstream : "
            + cause.getMessage());
        ctx.close();
    }
}