Normal Steps to Reproduce
Run the zk-springboot-jar demo project (with websockets enabled):
https://github.com/zkoss/zkspringboot/tree/master/zkspringboot-demos/zkspringboot- demo-jar
Open a page in chrome, perform some actions to verify that the websocket connection is established.
In chrome developer tools network panel, set network throttling to offline. (the websocket connection will start retrying to connect).
Shutdown the spring-boot application, and restart it (to purge the existing sessions).
Once the project has fully restarted, in chrome developer tools, network panel, set throttling to "no throttling"
Websocket connection is reestablished.
Current Result
2022-02-10 16:59:56.742 ERROR 17940 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception java.lang.NullPointerException: null at java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011) ~[na:1.8.0_312] at java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:1006) ~[na:1.8.0_312] at org.zkoss.zk.ui.http.ZKWebSocket.modifyHandshake(ZKWebSocket.java:59) ~[zk-9.6.1.jar:9.6.1] at org.apache.tomcat.websocket.server.UpgradeUtil.doUpgrade(UpgradeUtil.java:204) ~[tomcat-embed-websocket-9.0.50.jar:9.0.50] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:78) ~[tomcat-embed-websocket-9.0.50.jar:9.0.50] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.zkoss.zkmax.au.websocket.WebSocketFilter.doFilter(WebSocketFilter.java:71) ~[zkmax-9.6.1.jar:na] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.9.jar:5.3.9] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.9.jar:5.3.9] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.9.jar:5.3.9] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1723) [tomcat-embed-core-9.0.50.jar:9.0.50] at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.50.jar:9.0.50] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_312] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_312] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.50.jar:9.0.50] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_312]
Expected Result
Debug Information
@Override public void modifyHandshake(ServerEndpointConfig config, HandshakeRequest request, HandshakeResponse response) { //on reconnection, there is no matching sessions, so zkSession is null org.zkoss.zk.ui.Session zkSession = SessionsCtrl.getSession(WebApps.getCurrent(), request.getHttpSession()); ... //userProperties map doesn't accept null fields, cause NPE config.getUserProperties().put(tempSessionKey, zkSession); }
Workaround
currently no workaround (session has been already destroyed, and result is a "The resource you request is no longer available:" on the next user interaction with the page.