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前言
所谓心跳, 即在 TCP 长连接中, 客户端和服务器之间定期发送的一种特殊的数据包, 通知对方自己还在线, 以确保 TCP 连接的有效性.
这三个参数的含义：
- readerIdleTimeSeconds 读超时. 即当在指定的时间间隔内没有从 Channel 读取到数据时, 会触发一个 READER_IDLE 的IdleStateEvent 事件.
- writerIdleTimeSeconds 写超时. 即当在指定的时间间隔内没有数据写入到 Channel 时, 会触发一个 WRITER_IDLE 的IdleStateEvent 事件.
- allIdleTimeSeconds 读/写超时. 即当在指定的时间间隔内没有读或写操作时, 会触发一个 ALL_IDLE 的 IdleStateEvent 事件.
注：这三个参数默认的时间单位是秒。若需要指定其他时间单位，可以使用另一个构造方法： IdleStateHandler(boolean observeOutput, long readerIdleTime, long writerIdleTime, long allIdleTime, TimeUnit unit)
源码分析
要实现Netty服务端心跳检测机制需要在服务器端的ChannelInitializer中加入如下的代码：
pipeline.addLast(new IdleStateHandler(3, 0, 0, TimeUnit.SECONDS));
1. IdleStateHandler#channelRead
IdleStateHandler#channelRead方法，msg消息透传，不做任何业务了逻辑处理，让channelPipe中的下一个handler处理channelRead方法。
2.IdleStateHandler#channelActive
channelActive方法, 1. 初始化 2. channelActive 事件
initialize方法
private void initialize(ChannelHandlerContext ctx) {
// Avoid the case where destroy() is called before scheduling timeouts.
// See: https://github.com/netty/netty/issues/143
switch (state) {
case 1:
case 2:
return;
default:
break;
}
state = 1;
initOutputChanged(ctx);
lastReadTime = lastWriteTime = ticksInNanos();
if (readerIdleTimeNanos > 0) {
readerIdleTimeout = schedule(ctx, new ReaderIdleTimeoutTask(ctx),
readerIdleTimeNanos, TimeUnit.NANOSECONDS);
}
if (writerIdleTimeNanos > 0) {
writerIdleTimeout = schedule(ctx, new WriterIdleTimeoutTask(ctx),
writerIdleTimeNanos, TimeUnit.NANOSECONDS);
}
if (allIdleTimeNanos > 0) {
allIdleTimeout = schedule(ctx, new AllIdleTimeoutTask(ctx),
allIdleTimeNanos, TimeUnit.NANOSECONDS);
}
}
Netty心跳检测案例
HeartBeatServer
public class HeartBeatServer {
public static void main(String[] args) throws Exception {
EventLoopGroup boss = new NioEventLoopGroup();
EventLoopGroup worker = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(boss, worker)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("decoder", new StringDecoder());
pipeline.addLast("encoder", new StringEncoder());
//IdleStateHandler的readerIdleTime参数指定超过3秒还没收到客户端的连接，
//会触发IdleStateEvent事件并且交给下一个handler处理，下一个handler必须
//实现userEventTriggered方法处理对应事件
pipeline.addLast(new IdleStateHandler(3, 0, 0, TimeUnit.SECONDS));
pipeline.addLast(new HeartBeatServerHandler());
}
});
System.out.println("netty server start。。");
ChannelFuture future = bootstrap.bind(9000).sync();
future.channel().closeFuture().sync();
} catch (Exception e) {
e.printStackTrace();
} finally {
worker.shutdownGracefully();
boss.shutdownGracefully();
}
}
}
HeartBeatClient
public class HeartBeatClient {
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 ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("decoder", new StringDecoder());
pipeline.addLast("encoder", new StringEncoder());
pipeline.addLast(new HeartBeatClientHandler());
}
});
System.out.println("netty client start。。");
Channel channel = bootstrap.connect("127.0.0.1", 9000).sync().channel();
String text = "Heartbeat Packet";
Random random = new Random();
while (channel.isActive()) {
int num = random.nextInt(10);
Thread.sleep(2 * 1000);
channel.writeAndFlush(text);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
eventLoopGroup.shutdownGracefully();
}
}
static class HeartBeatClientHandler extends SimpleChannelInboundHandler<String> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
System.out.println(" client received :" + msg);
if (msg != null && msg.equals("idle close")) {
System.out.println(" 服务端关闭连接，客户端也关闭");
ctx.channel().closeFuture();
}
}
}
}
HeartBeatServerHandler
public class HeartBeatServerHandler extends SimpleChannelInboundHandler<String> {
int readIdleTimes = 0;
@Override
protected void channelRead0(ChannelHandlerContext ctx, String s) throws Exception {
System.out.println(" ====== > [server] message received : " + s);
if ("Heartbeat Packet".equals(s)) {
ctx.channel().writeAndFlush("ok");
} else {
System.out.println(" 其他信息处理 ... ");
}
}
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
IdleStateEvent event = (IdleStateEvent) evt;
String eventType = null;
switch (event.state()) {
case READER_IDLE:
eventType = "读空闲";
readIdleTimes++; // 读空闲的计数加1
break;
case WRITER_IDLE:
eventType = "写空闲";
// 不处理
break;
case ALL_IDLE:
eventType = "读写空闲";
// 不处理
break;
}
System.out.println(ctx.channel().remoteAddress() + "超时事件：" + eventType);
if (readIdleTimes > 3) {
System.out.println(" [server]读空闲超过3次，关闭连接，释放更多资源");
ctx.channel().writeAndFlush("idle close");
ctx.channel().close();
}
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
System.err.println("=== " + ctx.channel().remoteAddress() + " is active ===");
}
演示结果：
常见的心跳检测
比如说Nacos注册中心， Eureka注册中心等等，都有自己的心跳检测机制。
