netty中使用IdleStateHandler来发起心跳
时间:2015-07-07 17:18:35
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网络连接中,处理Idle事件是很常见的,一般情况下,客户端与服务端在指定时间内没有任何读写请求,就会认为连接是idle的。此时,客户端需要向服务端发送ping消息,来维持服务端与客户端的链接。那么怎么判断客户端在指定时间里没有任何读写请求呢?netty中为我们提供一个特别好用的IdleStateHandler来干这个苦差事!请看下面代码:
public class EchoClient { private final static int readerIdleTimeSeconds = 40;//读操作空闲30秒 private final static int writerIdleTimeSeconds = 50;//写操作空闲60秒 private final static int allIdleTimeSeconds = 100;//读写全部空闲100秒 public void connect(int port, String host) throws Exception { // 配置客户端NIO线程组 EventLoopGroup group = new NioEventLoopGroup(); try { Bootstrap b = new Bootstrap(); b.group(group).channel(NioSocketChannel.class) .option(ChannelOption.TCP_NODELAY, true) .handler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel ch) throws Exception { ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()); ch.pipeline().addLast("idleStateHandler", new IdleStateHandler(readerIdleTimeSeconds, writerIdleTimeSeconds,allIdleTimeSeconds)); ch.pipeline().addLast( new DelimiterBasedFrameDecoder(1024, delimiter)); ch.pipeline().addLast(new StringDecoder()); ch.pipeline().addLast(new EchoClientHandler()); } }); // 发起异步连接操作 ChannelFuture f = b.connect(host, port).sync(); // 当代客户端链路关闭 f.channel().closeFuture().sync(); } finally { // 优雅退出,释放NIO线程组 group.shutdownGracefully(); } } /** * @param args * @throws Exception */ public static void main(String[] args) throws Exception { int port = 8080; if (args != null && args.length > 0) { try { port = Integer.valueOf(args[0]); } catch (NumberFormatException e) { // 采用默认值 } } new EchoClient().connect(port, "127.0.0.1"); } }
在netty的客户端中添加:
ch.pipeline().addLast("idleStateHandler", new IdleStateHandler(readerIdleTimeSeconds, writerIdleTimeSeconds,allIdleTimeSeconds));
这个处理器,它的作用就是用来检测客户端的读取超时的,该类的第一个参数是指定读操作空闲秒数,第二个参数是指定写操作的空闲秒数,第三个参数是指定读写空闲秒数,当有操作操作超出指定空闲秒数时,便会触发UserEventTriggered事件。所以我们只需要在自己的handler中截获该事件,然后发起相应的操作即可(比如说发起ping操作)。以下是我们自定义的handler中的代码:
public class EchoClientHandler extends ChannelHandlerAdapter { private int counter; static final String ECHO_REQ = "Hi, Lilinfeng. Welcome to Netty.$_"; public EchoClientHandler() { } @Override public void channelActive(ChannelHandlerContext ctx) { for (int i = 0; i < 10; i++) { ctx.writeAndFlush(Unpooled.copiedBuffer(ECHO_REQ.getBytes())); } } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { System.out.println("This is " + ++counter + " times receive server : [" + msg + "]"); } @Override public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { cause.printStackTrace(); ctx.close(); } @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception { if (IdleStateEvent.class.isAssignableFrom(evt.getClass())) { IdleStateEvent event = (IdleStateEvent) evt; if (event.state() == IdleState.READER_IDLE) System.out.println("read idle"); else if (event.state() == IdleState.WRITER_IDLE) System.out.println("write idle"); else if (event.state() == IdleState.ALL_IDLE) System.out.println("all idle"); } }
这里,我们重点看重新的 userEventTriggered方法:
首先,判断evt事件是不是IdleStateEvent事件;
然后,继续判断是读空闲事件还是写空闲事件还是读写空闲事件;
最后,根据不同事件类型发起相应的操作
好了,现在回到我们的主题,我们的目的是在客户端在写空闲超时时,客户端主动发起一次平操作,所以我们只需要判断写空闲超时,发起ping操作即可!
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