参考源码：
文章参考：
机制图解：
注：websocket基于tcp协议，它在第一次连接时发起http请求，之后建立握手
在websocket中设置setConnectionLostTimeout参数，解释为：Setter for the interval checking for lost connections，意思是间隔检查连接是否丢失
整体是调用顺序为：onWebsocketOpen -》 startConnectionLostTimer -》 restartConnectionLostTimer-》 scheduleAtFixedRate -》 executeConnectionLostDetection
关键代码
this.connectionLostTimeout = TimeUnit.SECONDS.toNanos(connectionLostTimeout);
if (this.connectionLostTimeout <= ) {
log.trace("Connection lost timer stopped");
cancelConnectionLostTimer();
return;
}
long minimumPongTime = (long) (System.nanoTime() - ( connectionLostTimeout * 1.5 ));
for( WebSocket conn : connections ) {
executeConnectionLostDetection(conn, minimumPongTime);
}
WebSocketImpl webSocketImpl = (WebSocketImpl) webSocket;
if( webSocketImpl.getLastPong() < minimumPongTime ) {
log.trace("Closing connection due to no pong received: {}", webSocketImpl);
webSocketImpl.closeConnection( CloseFrame.ABNORMAL_CLOSE, "The connection was closed because the other endpoint did not respond with a pong in time. For more information check: https://github.com/TooTallNate/Java-WebSocket/wiki/Lost-connection-detection" );
} else {
if( webSocketImpl.isOpen() ) {
webSocketImpl.sendPing();
} else {
log.trace("Trying to ping a non open connection: {}", webSocketImpl);
}
}
connectionLostTimeout在设置后会转为纳秒时间， minimumPongTime为当前纳秒时间减去connectionLostTimeout的1.5倍，当最后一次Pong的时间小于minimumPongTime时产生close，即在间隔时间内未收到Pong响应关闭连接。如果正常则继续发送ping，即调用sendPing。
在服务端收到ping的时候，立即下发pong，两者的容忍时间为connectionLostTimeout是1.5倍，即设十秒的话就是容忍十五秒。当网络发生异常时，两者情况，服务端没有收到ping亦或者客户端没有收到pong，触发close。