Netty多客户端通信

【模拟多客户端上线通知，下线通知，服务器会通知其他客户端】

MyChatServer.java

public class MyChatServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
                    .childHandler(new MyChatServerInitializer());
            ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
            channelFuture.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

MyChatServerInitializer.java

public class MyChatServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));
        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        pipeline.addLast(new MyChatServerHandler());
    }
}

MyChatServerHandler.java

package com.dongqiang.netty.thirdexample;

import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.util.concurrent.GlobalEventExecutor;

/**
 * Created by dongqiang on 2017/6/11.
 */
public class MyChatServerHandler extends SimpleChannelInboundHandler<String> {

    private static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.forEach(ch -> {
            if(channel != ch) {
                ch.writeAndFlush(channel.remoteAddress() + " 发送的消息：" + msg + "\n");
            } else {
                ch.writeAndFlush("[自己] " + msg + "\n");
            }
        });
    }

    /**
     * 客户端与服务器建立连接，通知上线
     * @param ctx
     * @throws Exception
     */
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush("[服务器] - " + channel.remoteAddress() + " 加入\n");
        channelGroup.add(channel);
    }

    /**
     * 连接断开，通知下线
     */
    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush("[服务器] - " + channel.remoteAddress() + " 离开\n");
        //channelGroup.remove(channel);//这行代码用不用都可以，因为netty会自动调用它
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println("[服务器] - " + channel.remoteAddress() + " 上线\n");
    }


    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println("[服务器] - " + channel.remoteAddress() + " 下线\n");
    }

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

正如注释中所写，当客户端连接到服务端的时候，执行handlerAdd()，然后会执行channelActive()，当客户端断开的时候，先会执行channelInactive()，然后执行handlerRemoved()。这里服务端自己记录客户端上线和下线，并在channelActive()和channelInactive()通知其他客户端。ChannelGroup的作用就是为了控制客户端给其他客户端发消息。

看看客户端的代码：

MyChatClient.java

public class MyChatClient {
    public static void main(String[] args) throws Exception {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class).handler(new MyChatClientInitializer());
            Channel channel = bootstrap.connect("localhost", 8899).sync().channel();

            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            for(;;) {
                channel.writeAndFlush(br.readLine() + "\r\n");
            }
        } finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

这里用了一个循环，从标准输入中读取数据，然后写到服务端，服务端通过代码控制，将消息转发给其他客户端。

MyChatClientInitializer.java

package com.dongqiang.netty.thirdexample;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.Delimiters;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;

/**
 * Created by dongqiang on 2017/6/11.
 */
public class MyChatClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));
        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        pipeline.addLast(new MyChatClientHandler());

    }
}

MyClientHandler.java

package com.dongqiang.netty.thirdexample;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

/**
 * Created by dongqiang on 2017/6/11.
 */
public class MyChatClientHandler extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(msg);
    }
}

两个客户端依次启动：

在第一个客户端观察第二个客户端启动：

第二个客户端观察第一个客户端下线：

从server看：