Problem1: 服務端報錯：Broken pipe
java.io.IOException: Connection timed out
at sun.nio.ch.FileDispatcherImpl.read0(Native Method)
at sun.nio.ch.SocketDispatcher.read(SocketDispatcher.java:39)
at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223)
at sun.nio.ch.IOUtil.read(IOUtil.java:197)
at sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:380)
at org.apache.tomcat.util.net.SecureNioChannel.read(SecureNioChannel.java:581)
at org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper.fillReadBuffer(NioEndpoint.java:1248)
at org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper.fillReadBuffer(NioEndpoint.java:1221)
at org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper.read(NioEndpoint.java:1194)
at org.apache.tomcat.websocket.server.WsFrameServer.onDataAvailable(WsFrameServer.java:72)
at org.apache.tomcat.websocket.server.WsFrameServer.doOnDataAvailable(WsFrameServer.java:171)
at org.apache.tomcat.websocket.server.WsFrameServer.notifyDataAvailable(WsFrameServer.java:151)
at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.upgradeDispatch(WsHttpUpgradeHandler.java:148)
at org.apache.coyote.http11.upgrade.UpgradeProcessorInternal.dispatch(UpgradeProcessorInternal.java:54)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:53)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
05-Nov-2018 09:17:07.881 INFO [https-jsse-nio-443-exec-6] org.apache.tomcat.websocket.server.WsRemoteEndpointImplServer.doClose Failed to close the ServletOutputStream connection cleanly
java.io.IOException: Broken pipe
at sun.nio.ch.FileDispatcherImpl.write0(Native Method)
at sun.nio.ch.SocketDispatcher.write(SocketDispatcher.java:47)
at sun.nio.ch.IOUtil.writeFromNativeBuffer(IOUtil.java:93)
at sun.nio.ch.IOUtil.write(IOUtil.java:65)
at sun.nio.ch.SocketChannelImpl.write(SocketChannelImpl.java:471)
at org.apache.tomcat.util.net.SecureNioChannel.flush(SecureNioChannel.java:144)
at org.apache.tomcat.util.net.SecureNioChannel.close(SecureNioChannel.java:526)
at org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper.close(NioEndpoint.java:1209)
at org.apache.tomcat.websocket.server.WsRemoteEndpointImplServer.doClose(WsRemoteEndpointImplServer.java:167)
at org.apache.tomcat.websocket.WsRemoteEndpointImplBase.close(WsRemoteEndpointImplBase.java:710)
at org.apache.tomcat.websocket.WsSession.onClose(WsSession.java:518)
at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.close(WsHttpUpgradeHandler.java:240)
at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.upgradeDispatch(WsHttpUpgradeHandler.java:162)
at org.apache.coyote.http11.upgrade.UpgradeProcessorInternal.dispatch(UpgradeProcessorInternal.java:54)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:53)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
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報出超時的原因可能是后端在向前端發起數據請求時，沒有成功。可能的原因是，在服務端，負責和前端通信的websocket連接Session存放在一個Map中，當由於某種未知的原因，導致前后端連接斷開后，即客戶端失聯了，但是Map里的Session並未被移除。所以當服務端有新消息要發送給這個已經失聯的Session，便會報錯：Connection timed out, Broken pipe。
Solution：當產生這個異常后，后端從Map中移除(remove)已斷開連接的客戶端Session。
Note：也可以在前端把錯誤打印出來：WebSocket斷開時，會觸發CloseEvent, CloseEvent的code字段表示了WebSocket斷開的原因。可以從該字段中分析斷開的原因。
CloseEvent的三個字段：
CloseEvent.code: code是錯誤碼，是整數類型
CloseEvent.reason: reason是斷開原因，是字符串
CloseEvent.wasClean: wasClean表示是否正常斷開，是布爾值。一般異常斷開時，該值為false
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websocket.onclose = function (e) {
console.log('WebSocket連接斷開：Code:' + e.code + ' Reason:' + e.reason + ' wasClean:' + e.wasClean);
}
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Problem2: 客戶端斷開后，如何做到嘗試再次連接，即斷線重連
Solution: websocket斷線重連解決方案: ReconnectingWebSocket
let ws = new WebSocket('ws://host:port');
// 替換為：
let ws = new ReconnectingWebSocket('ws://host:port');
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當然ReconnectingWebSocket中還有其他諸如重試間隔等各類配置項，可以查看文檔或源碼。
Note：如果服務器域名為HTTPS，那么使用的WebSocket協議也必須是wss
If you have any questions or any bugs are found, please feel free to contact me.
Your comments and suggestions are welcome!