检测空闲连接和超时是为了及时释放资源。常见的方法发送消息用于测试一个不活跃的连接来,通常称为“心跳”,到远端来确定它是否还活着。(一个更激进的方法是简单地断开那些指定的时间间隔的不活跃的连接)。 处理空闲连接是一项常见的任务,Netty 提供了几个 ChannelHandler 实现此目的。表8.4概述。 Table 8.4 ChannelHandlers for idle connections and timeouts | 名称 | 描述 | | --- | --- | | IdleStateHandler | fires an IdleStateEvent if the connection idles too long. You can then handle the IdleStateEvent by overriding the userEventTriggered(...) method in your ChannelInboundHandler. | | ReadTimeoutHandler | throws a ReadTimeoutException and closes the Channel when no inbound | data is received for a specified interval. The ReadTimeoutException can be detected by overriding the exceptionCaught(...) method of your ChannelHandler. WriteTimeoutHandler | throws a WriteTimeoutException and closes the Channel when no inbound data is received for a specified interval. The WriteTimeoutException can be detected by overriding the exceptionCaught(...) method of your ChannelHandler. 详细看下 IdleStateHandler，下面是一个例子，当超过60秒没有数据收到时，就会得到通知，此时就发送心跳到远端，如果没有回应，连接就关闭。 Listing 8.7 Sending heartbeats ~~~ public class IdleStateHandlerInitializer extends ChannelInitializer<Channel> { @Override protected void initChannel(Channel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); pipeline.addLast(new IdleStateHandler(0, 0, 60, TimeUnit.SECONDS)); //1 pipeline.addLast(new HeartbeatHandler()); } public static final class HeartbeatHandler extends ChannelInboundHandlerAdapter { private static final ByteBuf HEARTBEAT_SEQUENCE = Unpooled.unreleasableBuffer( Unpooled.copiedBuffer("HEARTBEAT", CharsetUtil.ISO_8859_1)); //2 @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception { if (evt instanceof IdleStateEvent) { ctx.writeAndFlush(HEARTBEAT_SEQUENCE.duplicate()) .addListener(ChannelFutureListener.CLOSE_ON_FAILURE); //3 } else { super.userEventTriggered(ctx, evt); //4 } } } } ~~~ 1. IdleStateHandler 将通过 IdleStateEvent 调用 userEventTriggered ，如果连接没有接收或发送数据超过60秒钟 2. 心跳发送到远端 3. 发送的心跳并添加一个侦听器，如果发送操作失败将关闭连接 4. 事件不是一个 IdleStateEvent 的话，就将它传递给下一个处理程序 总而言之,这个例子说明了如何使用 IdleStateHandler 测试远端是否还活着，如果不是就关闭连接释放资源。