关于关闭服务端或者客户端时另一端马上抛异常问题

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长连接和心跳机制可以检测链路的有效性，但是我注释了服务端的keep_alive配置，也注释了服务端和客户端中的心跳机制的代码，当我强制关闭服务端或者客户端，另一端马上就能感知到链路断开了，抛出链路断开异常。我想知道在没有长连接和心跳机制的情况下，是怎么感知到链路断开的？ 下面是抛出的异常。

java.io.IOException: 远程主机强迫关闭了一个现有的连接。 at sun.nio.ch.SocketDispatcher.read0(Native Method) at sun.nio.ch.SocketDispatcher.read(SocketDispatcher.java:43) at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223) at sun.nio.ch.IOUtil.read(IOUtil.java:192) at sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:380) at io.netty.buffer.PooledByteBuf.setBytes(PooledByteBuf.java:247) at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1147) at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:347) at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:148) at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:700) at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:635) at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:552) at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:514) at io.netty.util.concurrent.SingleThreadEventExecutor$6.run(SingleThreadEventExecutor.java:1044) at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) at java.lang.Thread.run(Thread.java:748)