netty解决channel管理，可广播消息

在Netty中提供了ChannelGroup接口，该接口继承Set接口，因此可以通过ChannelGroup可管理服务器端所有的连接的Channel，然后对所有的连接Channel广播消息。

Server端：

public class BroadCastServer {

    public static void run(int port) {
        EventLoopGroup boss = new NioEventLoopGroup();
        EventLoopGroup worker = new NioEventLoopGroup();
        try {
            ServerBootstrap bootstrap = new ServerBootstrap();
            bootstrap.group(boss, worker)
                     .channel(NioServerSocketChannel.class)                // 设置Channel Type
                     .option(ChannelOption.SO_BACKLOG, 1024)            // 设置Channel属性
                     .childHandler(new ChannelInitializer<SocketChannel>() {

                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
                            pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));
                            pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8));
                            pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8));
                            pipeline.addLast(new BroadCastChannelHandler());
                        }
                    });
            ChannelFuture channelFuture = bootstrap.bind(port).sync();
            if (channelFuture.isDone()) {
                System.out.println(String.format("server bind port %s sucess", port));
            }
            Channel channel = channelFuture.channel();
            /**CloseFuture异步方式关闭*/
            channel.closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            boss.shutdownGracefully();
            worker.shutdownGracefully();
        }
    }

    public static void main(String []args) {
        BroadCastServer.run(8080);
    }
        
}

public class BroadCastChannelHandler extends ChannelInboundHandlerAdapter {

    private static final Gson GSON = new GsonBuilder().create();
    
    private static final SimpleDateFormat SDF = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    
    private static final AtomicInteger response = new AtomicInteger();
    
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel ch = ctx.channel();
        if (ChannelGroups.size() > 0) {
            Message msg = new Message(ch.remoteAddress().toString().substring(1), SDF.format(new Date()));
            ChannelGroups.broadcast(GSON.toJson(msg), new ChannelMatchers());
        }
        ChannelGroups.add(ch);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        Channel ch = ctx.channel();
        if (ChannelGroups.contains(ch) && String.valueOf(msg).equals("welcome")) {
            System.out.println(String.format("receive [%s] from [%s] at [%s]", String.valueOf(msg) ,
                                    ch.remoteAddress().toString().substring(1), SDF.format(new Date())));
            response.incrementAndGet();
        }
        synchronized (response) {
            System.out.println(response.get() + "	" + ChannelGroups.size());
            if (response.get() == ChannelGroups.size() - 1) {
                System.out.println("server close all connected channel");
                ChannelGroups.disconnect();
                response.set(0);
            }
        }
    }
    
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }
    
    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        ctx.close();
    }
    
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ChannelGroups.discard(ctx.channel());
        response.decrementAndGet();
    }

    public static class ChannelMatchers implements ChannelMatcher {

        @Override
        public boolean matches(Channel channel) {
            return true;
        }
        
    }
    
}

服务器端收到所有连接客户端对广播消息的响应后，服务器端主动关闭已连接的Channel

客户端：

public class Client	{

	private static final String host = "127.0.0.1";
	
	private static final int port = 8080;
	
	private static final ExecutorService es = Executors.newFixedThreadPool(5);
	
	public static void start() {
		for (int i = 0; i < 5; i++) {
			es.execute(new Task());
		}
		es.shutdown();
	}
	
	public static class Task implements Runnable {

		@Override
		public void run() {
			EventLoopGroup group = new NioEventLoopGroup();
			try {
				Bootstrap bootstrap = new Bootstrap();
				bootstrap.group(group)
						 .channel(NioSocketChannel.class)
						 .option(ChannelOption.TCP_NODELAY, true)
						 .handler(new ChannelInitializer<SocketChannel>() {

							@Override
							protected void initChannel(SocketChannel ch) throws Exception {
								ChannelPipeline pipeline = ch.pipeline();
								pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
								pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));
								pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8));
								pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8));
								pipeline.addLast(new SimpleClientChannelHandler());
							}
							
						});
				ChannelFuture channelFuture = bootstrap.connect(host, port).sync();
				if (channelFuture.isSuccess()) {
					System.out.println(String.format("connect server(%s:%s) sucess", host, port));
				}
				channelFuture.channel().closeFuture().sync();
			} catch (InterruptedException e) {
				e.printStackTrace();
			} finally {
				group.shutdownGracefully();
			}
		}
		
	}
	
	public static void main(String []args) {
		Client.start();
	}
}


public class SimpleClientChannelHandler extends ChannelInboundHandlerAdapter {

	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
		Channel channel = ctx.channel();
		System.out.println(String.format("client(%s) receive message [%s]", channel.localAddress().toString().substring(1), 
								String.valueOf(msg)));
		System.out.println();
		ctx.writeAndFlush(String.valueOf("welcome"));
	}

	@Override
	public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
		ctx.disconnect(ctx.newPromise());
		ctx.close();
		System.out.println(String.format("client(%s) close sucess", ctx.channel().localAddress().toString().substring(1)));
	}
}

　　本文使用ChannelGroups辅助类管理服务器端已连接的Channel，代码实现如下:

public class ChannelGroups {

    private static final ChannelGroup CHANNEL_GROUP = new DefaultChannelGroup("ChannelGroups", GlobalEventExecutor.INSTANCE);
    
    public static void add(Channel channel) {
        CHANNEL_GROUP.add(channel);
    }
    
    public static ChannelGroupFuture broadcast(Object msg) {
        return CHANNEL_GROUP.writeAndFlush(msg);
    }
    
    public static ChannelGroupFuture broadcast(Object msg, ChannelMatcher matcher) {
        return CHANNEL_GROUP.writeAndFlush(msg, matcher);
    }
    
    public static ChannelGroup flush() {
        return CHANNEL_GROUP.flush();
    }
    
    public static boolean discard(Channel channel) {
        return CHANNEL_GROUP.remove(channel);
    }
    
    public static ChannelGroupFuture disconnect() {
        return CHANNEL_GROUP.disconnect();
    }
    
    public static ChannelGroupFuture disconnect(ChannelMatcher matcher) {
        return CHANNEL_GROUP.disconnect(matcher);
    }
    
    public static boolean contains(Channel channel) {
        return CHANNEL_GROUP.contains(channel);
    }
    
    public static int size() {
        return CHANNEL_GROUP.size();
    }
}