Netty的Echo示例

1.简述

　　Echo客户端和服务器之间的交互是非常简单的。在客户端建立一个连接之后，它会向服务器发送一个或多个消息，反过来，服务器又会将每个消息回送给客户端。虽然它本身看起来好像用处不大，但它充分地体现了客户端/服务器系统中典型的请求-响应交互模式。

　　通过同时实现客户端和服务器，我们将能够更加全面地理解Netty的API。

2.示例代码

（1）Maven引入

<dependencies>
        <!-- https://mvnrepository.com/artifact/io.netty/netty-all -->
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.36.Final</version>
        </dependency>
    </dependencies>

（2）服务器

　　EchoServer：

import io.netty.bootstrap.ServerBootstrap;
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 java.net.InetSocketAddress;

/**
 * @description: echo服务器
 **/
public class EchoServer {
    private static final int port = 8080;//服务器监听端口

    public void start() throws InterruptedException {
        ServerBootstrap server = new ServerBootstrap();//引导辅助程序
        EventLoopGroup group = new NioEventLoopGroup();//通过nio方式来接收连接和处理连接
        try {
            server.group(group);
            server.channel(NioServerSocketChannel.class);//设置nio类型的channel
            server.localAddress(new InetSocketAddress(port));//设置监听端口
            server.childHandler(new ChannelInitializer<SocketChannel>() {//有连接到达时会创建一个channel
                protected void initChannel(SocketChannel ch) {
                    //pipeline管理channel中的Handler，在channel队列中添加一个handler来处理业务
                    ch.pipeline().addLast("serverHandler", new EchoServerHandler());
                }
            });
            ChannelFuture f = server.bind().sync();//配置完成，开始绑定server，通过调用sync同步方法阻塞直到绑定成功
            System.out.println(EchoServer.class.getName() + " 开始监听 " + f.channel().localAddress());
            f.channel().closeFuture().sync();//应用程序会一直等待，直到channel关闭
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            group.shutdownGracefully().sync();//关闭EventLoopGroup，释放掉所有资源包括创建的线程
        }
    }

    public static void main(String[] args) {
        try {
            new EchoServer().start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

　　EchoServerHandler：

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;

/**
 * @description: echo服务器业务处理类
 * Sharable表示此对象在channel间共享
 **/
@ChannelHandler.Sharable//注解@Sharable可以让它在channels间共享
public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        ByteBuf in = (ByteBuf) msg;
        System.out.println("服务器收到"+ctx.channel().localAddress()+"数据 :" + in.toString(CharsetUtil.UTF_8));
        //将接收到的消息写给发送者，即客户端，而不冲刷出站消息
        ctx.write(msg);
    }

    public void channelReadComplete(ChannelHandlerContext ctx) {
        //将未决消息冲刷到远程节点，并且关闭该Channel
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
    }

    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        //cause.printStackTrace();//捕捉异常信息
        System.out.println(cause.getMessage());
        ctx.close();//出现异常时关闭channel
    }
}

（3）客户端

　　EchoClient：

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
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 java.net.InetSocketAddress;

/**
 * @description: echo客户端
 **/
public class EchoClient {
    private final String host;
    private final int port;

    public EchoClient(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group);
            b.channel(NioSocketChannel.class);
            b.remoteAddress(new InetSocketAddress(host, port));
            b.handler(new ChannelInitializer<SocketChannel>() {
                public void initChannel(SocketChannel ch) {
                    ch.pipeline().addLast(new EchoClientHandler());
                }
            });
            ChannelFuture f = b.connect().sync();
            f.addListener(new ChannelFutureListener() {
                public void operationComplete(ChannelFuture future) {
                    if(future.isSuccess()){
                        System.out.println("连接echo服务器成功");
                    }else{
                        System.out.println("连接echo服务器失败："+future.cause().getMessage());
                        //future.cause().printStackTrace();
                    }
                }
            });
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }

    public static void main(String[] args) throws Exception {
        for (int i=0;i<100;i++) {
            new Thread(new Runnable() {
                public void run() {
                    try {
                        new EchoClient("127.0.0.1", 8080).start();
                    }catch (Exception e){
                        e.printStackTrace();
                    }
                }
            }).start();
        }
    }
}

　　EchoClientHandler：

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.CharsetUtil;

/**
 * @description: echo客户端业务处理类
 **/
@ChannelHandler.Sharable
public class EchoClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
    /**
     *此方法会在连接到服务器后被调用
     * */
    public void channelActive(ChannelHandlerContext ctx) {
        ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks!", CharsetUtil.UTF_8));
    }

    /**
     *此方法会在接收到服务器数据后调用
     * */
    public void channelRead0(ChannelHandlerContext ctx, ByteBuf in) {
        System.out.println("客户端收到数据: " + in.toString(CharsetUtil.UTF_8));
    }

    /**
     *捕捉到异常
     * */
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        cause.printStackTrace();
        ctx.close();
    }

}