1.介绍

ChannelGroup是一个线程安全的集合，它提供了打开一个Channel和不同批量的方法。可以使用ChannelGroup来讲Channel分类到一个有特别意义的组中。当组中的channel关闭时会自动从组中移除，因此我们不需要担心添加进去的channel的生命周期。一个channel可以属于多个ChannelGroup。

当一个ChannelGroup中即存在ServerChanel又存在non-ServerChannel时，执行IO操作时会优先执行ServerChannel中的方法。

2.方法说明

    //返回ChannelGroup的名称
    String name();

    //通过channelId查找相应的Channel
    Channel find(ChannelId id);
    
    //异步地将消息写到所有的Channel中
    ChannelGroupFuture write(Object message);

    ChannelGroupFuture write(Object message, ChannelMatcher matcher);

    ChannelGroupFuture write(Object message, ChannelMatcher matcher, boolean voidPromise);

    ChannelGroup flush();

    ChannelGroup flush(ChannelMatcher matcher);

    ChannelGroupFuture writeAndFlush(Object message);

    @Deprecated
    ChannelGroupFuture flushAndWrite(Object message);

    ChannelGroupFuture writeAndFlush(Object message, ChannelMatcher matcher);

    ChannelGroupFuture writeAndFlush(Object message, ChannelMatcher matcher, boolean voidPromise);

    @Deprecated
    ChannelGroupFuture flushAndWrite(Object message, ChannelMatcher matcher);

    //将所有通道与远程端断开连接
    ChannelGroupFuture disconnect();

    ChannelGroupFuture disconnect(ChannelMatcher matcher);

    //关闭所有的通道
    ChannelGroupFuture close();

    ChannelGroupFuture close(ChannelMatcher matcher);

    @Deprecated
    ChannelGroupFuture deregister();

    @Deprecated
    ChannelGroupFuture deregister(ChannelMatcher matcher);

    //返回一个ChannelGroupFuture，当所有的channel关闭时，会得到相应的通知
    ChannelGroupFuture newCloseFuture();

    ChannelGroupFuture newCloseFuture(ChannelMatcher matcher);

3.示例

  public class MyHandler extends SimpleChannelInboundHandler<TextWebSocketFrame> {

    //channel对象数组
    private static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {
        System.out.println("channelRead0执行了");
        Channel channel = ctx.channel();

        channelGroup.forEach(ch -> {
            if(channel != ch){
                ch.writeAndFlush(new TextWebSocketFrame(channel.remoteAddress() + " 发送的消息 ："+msg.text()));
            }else{
                ch.writeAndFlush(new TextWebSocketFrame("[自己] "+msg.text()));
            }
        });
    }

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        System.out.println("handlerAdded执行了");
        Channel channel = ctx.channel();

        //广播消息
        channelGroup.writeAndFlush(new TextWebSocketFrame("[服务器] - "+channel.remoteAddress()+"加入"));
        channelGroup.add(channel);
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush(new TextWebSocketFrame("[服务器] -"+ channel.remoteAddress() +"离开"));
    }


    //该方法发出的消息，自身channel还未形成所以不能收到消息
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush(new TextWebSocketFrame(channel.remoteAddress() + "上线了"));
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush(new TextWebSocketFrame(channel.remoteAddress() + "下线了"));
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("异常发生");
        ctx.close();
    }
}