什么是心跳检测
心跳检测指的是在客户端和服务端维护一种特殊的数据包，客户端通过这个数据包告诉服务端自己还是存活的，然后服务端可以通过这个心跳检测机制去实现一些业务功能，如：空闲自动断开、判断客户端是否在线等
如何实现心跳检测机制
其实只需要引入IdleStateHandler，就搞定了
代码语言：javascript复制try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(bossGroup, workerGroup) //设置两个线程组
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.info("客户端channel 初始化");
ch.pipeline().addLast(new IdleStateHandler(3,3,3, TimeUnit.SECONDS));
ch.pipeline().addLast(new NettyServerHandler());
}
});
ChannelFuture cf = bootstrap.bind(9999).sync();
log.info("服务启动成功....");
cf.addListener((ChannelFutureListener) future -> log.info("监听端口:{}",future.isSuccess()));
cf.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
心跳检测机制工作原理
进入源码之后，我们可以发现IdleStateHandler内部定义的一些结构
初始化构造器后
定义了读、写、读写 事件
触发channelActive后
代码语言：javascript复制@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
// This method will be invoked only if this handler was added
// before channelActive() event is fired. If a user adds this handler
// after the channelActive() event, initialize() will be called by beforeAdd().
initialize(ctx);
super.channelActive(ctx);
}
调用了initialize(ctx);，我们点进去看看里面做了什么
代码语言：javascript复制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;
}
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);
}
}
通过我们的配置，分别schedule三个任务：ReaderIdleTimeoutTask、WriterIdleTimeoutTask、AllIdleTimeoutTask
定时执行task
这里拿ReaderIdleTimeoutTask进行说明
代码语言：javascript复制private final class ReaderIdleTimeoutTask extends AbstractIdleTask {
ReaderIdleTimeoutTask(ChannelHandlerContext ctx) {
super(ctx);
}
@Override
protected void run(ChannelHandlerContext ctx) {
long nextDelay = readerIdleTimeNanos;
if (!reading) {
nextDelay -= ticksInNanos() - lastReadTime;
}
if (nextDelay <= 0) {
// Reader is idle - set a new timeout and notify the callback.
readerIdleTimeout = schedule(ctx, this, readerIdleTimeNanos, TimeUnit.NANOSECONDS);
boolean first = firstReaderIdleEvent;
firstReaderIdleEvent = false;
try {
IdleStateEvent event = newIdleStateEvent(IdleState.READER_IDLE, first);
channelIdle(ctx, event);
} catch (Throwable t) {
ctx.fireExceptionCaught(t);
}
} else {
// Read occurred before the timeout - set a new timeout with shorter delay.
readerIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
}
}
}
- 获取读空闲的时长
- 如果当前没有在读，则将当前时间剪去上次读取channel的时间做差值，然后将配置的空闲时长剪去这个差值，得到 新的nextDelay
- 如果nextDelay小于0，则说明，距离上次读取channel的时间已经超过了程序配置的时间
- 重新schedule一个新的task，时间重置
- 触发IdleStateEvent 时间，一般业务逻辑回去订阅这个事件
- 如果大于0，则按照新的delay重新schedule一个task
编写业务逻辑，实现空闲自动断开
代码语言：javascript复制@Slf4j
class NettyServerHandler extends ChannelInboundHandlerAdapter {
int i=0;
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
ByteBuf byteBuf = (ByteBuf) msg;
log.info("第{}次收到客户端消息:{}n",i ,byteBuf.readableBytes());
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) {
}
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
if (evt instanceof IdleStateEvent) {
IdleStateEvent idleStateEvent = (IdleStateEvent) evt;
switch (idleStateEvent.state()) {
case ALL_IDLE:
log.error("读写都空闲");
break;
case READER_IDLE:
log.error("读空闲");
break;
case WRITER_IDLE:
log.error("写空闲");
break;
}
}
}
}
