java網絡通訊：netty

Netty提供異步的、事件驅動的網絡應用程序框架和工具，用以快速開發高性能、高可靠性的網絡服務器和客戶端程序。

也就是說，Netty 是一個基於NIO的客戶，服務器端編程框架，使用Netty 能夠確保你快速和簡單的開發出一個網絡應用，例如實現了某種協議的客戶，服務端應用。Netty至關簡化和流線化了網絡應用的編程開發過程，例如，TCP和UDP的socket服務開發。

本文示例採用netty 5.0。上代碼.

服務端:

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 {
        // 配置服務端的NIO，循環事件線程組
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();//配置類
            //NioServerSocketChannel做爲channel類，它的功能對應於JDK NIO類庫中的ServerSocketChannel
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new TimeServerHandler());//綁定事件處理類
            // 綁定端口，同步等待成功
            ChannelFuture f = b.bind(port).sync();

            // 等待服務端監聽端口關閉
            f.channel().closeFuture().sync();
        } finally {
            // 優雅退出，釋放線程池資源
            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) {
                // 採用默認值
            }
        }
        new TimeServer().bind(port);
    }
}

服務端事務處理類:

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 {
　　/*當有數據時，自動調用，讀取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();
    }
}

客戶端：

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 {
        // 配置客戶端NIO線程組
        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>匿名類初始化channel的pipeline，將客戶端事務處理類加入到隊列中
                        @Override
                        public void initChannel(SocketChannel ch)
                                throws Exception {
                            ch.pipeline().addLast(new TimeClientHandler());
                        }
                    });
            // 發起異步鏈接操做
            ChannelFuture f = b.connect(host, port).sync();

            // 當代客戶端鏈路關閉
            f.channel().closeFuture().sync();
        } finally {
            // 優雅退出，釋放NIO線程組
            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) {
        // 採用默認值
        }
    }
    new TimeClient().connect(port, "127.0.0.1");
    }
}

客戶端事件處理類：

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);
    }
　　/*鏈接成功後，自動發送消息*/ public void channelActive(ChannelHandlerContext ctx) {
    　　ctx.writeAndFlush(firstMessage);
    }
　　/*有消息返回時，自動調用該函數讀取*/ 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);
    }
　　/*發生異常時，自動調用*/ public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // 釋放資源
        logger.warning("Unexpected exception from downstream : "
            + cause.getMessage());
        ctx.close();
    }
}