Camunda token not moving through the flow upon programmatic state transition - spring-boot

Question

I've created a workflow prototype based on the original Camunda Twitter example with a couple of modifications described below.
When ran right out of the box, unmodified, the process token:
stops first at the Review Tweet user task:
and then when the task is completed:
the flow moves to its completion and the token symbol disappears from the diagram, as it should:
the following message correctly appearing in the Spring application log:
along with the following exception being thrown right afterwards, which doesn't seem to affect anything (or does it?):
2019-11-25 12:12:58.995 WARN 772 --- [nio-8080-exec-5] ExceptionHandler : org.camunda.bpm.engine.rest.exception.InvalidRequestException: No matching task with id 0830f1f6-0fa4-11ea-a773-00155d0a5b14
at org.camunda.bpm.engine.rest.sub.task.impl.TaskResourceImpl.getHalTask(TaskResourceImpl.java:198)
at org.camunda.bpm.engine.rest.sub.task.impl.TaskResourceImpl.getTask(TaskResourceImpl.java:180)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:76)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:148)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:191)
at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ObjectOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:216)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:103)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:493)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:415)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:104)
at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:277)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:272)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:268)
at org.glassfish.jersey.internal.Errors.process(Errors.java:316)
at org.glassfish.jersey.internal.Errors.process(Errors.java:298)
at org.glassfish.jersey.internal.Errors.process(Errors.java:268)
at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:289)
at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:256)
at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:703)
at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:416)
at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:370)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:389)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:342)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:229)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.camunda.bpm.engine.rest.filter.CacheControlFilter.doFilter(CacheControlFilter.java:45)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.camunda.bpm.engine.rest.filter.EmptyBodyFilter.doFilter(EmptyBodyFilter.java:101)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.camunda.bpm.webapp.impl.engine.ProcessEnginesFilter.applyFilter(ProcessEnginesFilter.java:130)
at org.camunda.bpm.webapp.impl.filter.AbstractTemplateFilter.doFilter(AbstractTemplateFilter.java:58)
at org.camunda.bpm.spring.boot.starter.webapp.filter.LazyDelegateFilter.doFilter(LazyDelegateFilter.java:60)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.camunda.bpm.webapp.impl.security.filter.headersec.HttpHeaderSecurityFilter.doFilter(HttpHeaderSecurityFilter.java:83)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.camunda.bpm.webapp.impl.security.filter.CsrfPreventionFilter.doFilter(CsrfPreventionFilter.java:165)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.camunda.bpm.webapp.impl.security.filter.SecurityFilter.doFilterSecure(SecurityFilter.java:71)
at org.camunda.bpm.webapp.impl.security.filter.SecurityFilter.doFilter(SecurityFilter.java:55)
at org.camunda.bpm.spring.boot.starter.webapp.filter.LazyDelegateFilter.doFilter(LazyDelegateFilter.java:60)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.camunda.bpm.webapp.impl.security.auth.AuthenticationFilter$1.execute(AuthenticationFilter.java:62)
at org.camunda.bpm.webapp.impl.security.auth.AuthenticationFilter$1.execute(AuthenticationFilter.java:60)
at org.camunda.bpm.webapp.impl.security.SecurityActions.runWithAuthentications(SecurityActions.java:44)
at org.camunda.bpm.webapp.impl.security.auth.AuthenticationFilter.doFilter(AuthenticationFilter.java:60)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:836)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1747)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
Now, I've created the following modifications to the original example:
a) Introduced an endpoint (/invoke) via which the process is initially invoked:
#RequestMapping(value= "/invoke", method = RequestMethod.POST, produces=MediaType.APPLICATION_JSON_VALUE,consumes=MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public String tweetWritten( #RequestBody CreateTweet data) {
Map<String, Object> context = new HashMap<>();
context.put("content", data.content);
context.put("email", data.email);
ProcessInstance processInstance = runtimeService.startProcessInstanceByKey("TwitterDemoProcessControlled",context);
String processInstanceId = processInstance.getProcessInstanceId();
logger.info("started instance: {}", processInstanceId);
return processInstanceId;
}
b) Introduced another endpoint (/review) intended to programmatically transition the flow from the User Task of reviewing the tweet:
#RequestMapping(value= "/review", method = RequestMethod.POST, produces=MediaType.APPLICATION_JSON_VALUE,consumes=MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public String reviewTweet( #RequestBody ReviewTweet data) {
boolean approved = data.approved;
String comments = data.comments;
Map<String, Object> context = new HashMap<>();
context.put("approved", approved);
context.put("comments", comments);
logger.info("Application approved: {} with comments: {}", approved, comments);
ProcessInstance processInstance = runtimeService.createProcessInstanceQuery().singleResult();
String processInstanceId = processInstance.getId();
logger.info("Instance from the query: {}", processInstanceId);
runtimeService.createProcessInstanceModification(processInstanceId)
.startAfterActivity("user_task_review_tweet")
.setVariable("approved", approved)
.setVariable("comments", comments)
.execute();
return processInstanceId;
}
When started via the /invoke endpoint:
curl -X POST \
http://localhost:8080/twitter-demo/invoke \
-H 'Accept: */*' \
-H 'Accept-Encoding: gzip, deflate' \
-H 'Cache-Control: no-cache' \
-H 'Connection: keep-alive' \
-H 'Content-Length: 95' \
-H 'Content-Type: application/json' \
-H 'Host: localhost:8080' \
-H 'Postman-Token: 420dfc61-f7c8-4480-bd1b-d1b4ab90c4ac,6b18c053-b43d-4de3-9f88-61b70f5ad812' \
-H 'User-Agent: PostmanRuntime/7.20.1' \
-H 'cache-control: no-cache' \
-d '{
"email": "s.l#abc.com",
"content": "This is the message to be twitted"
}'
Spring logs no longer register any exception:
2019-11-25 13:24:48.872 WARN 18188 --- [nio-8080-exec-4] o.glassfish.jersey.servlet.WebComponent : A servlet request to the URI http://localhost:8080/api/admin/auth/user/default/login/cockpit contains form parameters in the request body but the request body has been consumed by the servlet or a servlet filter accessing the request parameters. Only resource methods using #FormParam will work as expected. Resource methods consuming the request body by other means will not work as expected.
2019-11-25 13:25:29.168 INFO 18188 --- [nio-8080-exec-1] o.c.b.s.b.e.t.ProcessFlowController : started instance: f53c1e54-0fb0-11ea-b813-00155d0a5b14
and the Cockpit displays the token similar to how it shows in the original example above:
.
However after invoking the /review endpoint:
curl -X POST \
http://localhost:8080/twitter-demo/review \
-H 'Accept: */*' \
-H 'Accept-Encoding: gzip, deflate' \
-H 'Cache-Control: no-cache' \
-H 'Connection: keep-alive' \
-H 'Content-Length: 76' \
-H 'Content-Type: application/json' \
-H 'Host: localhost:8080' \
-H 'Postman-Token: 74ed1585-6330-4506-ab7b-0c5b8727de90,fae2ee8d-1e23-4006-bbf5-ff80453d754f' \
-H 'User-Agent: PostmanRuntime/7.20.1' \
-H 'cache-control: no-cache' \
-d '{
"approved": false,
"comments": "This does not deserve to be published"
}'
the token symbol count still stays at the Review Tweet task:
even though, according to the Spring logs, the process was successfully completed:
2019-11-25 13:24:48.872[0;39m [33m WARN[0;39m [35m18188[0;39m [2m---[0;39m [2m[nio-8080-exec-4][0;39m [36mo.glassfish.jersey.servlet.WebComponent [0;39m [2m:[0;39m A servlet request to the URI http://localhost:8080/api/admin/auth/user/default/login/cockpit contains form parameters in the request body but the request body has been consumed by the servlet or a servlet filter accessing the request parameters. Only resource methods using #FormParam will work as expected. Resource methods consuming the request body by other means will not work as expected.
[2m2019-11-25 13:25:29.168[0;39m [32m INFO[0;39m [35m18188[0;39m [2m---[0;39m [2m[nio-8080-exec-1][0;39m [36mo.c.b.s.b.e.t.ProcessFlowController [0;39m [2m:[0;39m started instance: f53c1e54-0fb0-11ea-b813-00155d0a5b14
[2m2019-11-25 13:28:09.385[0;39m [32m INFO[0;39m [35m18188[0;39m [2m---[0;39m [2m[nio-8080-exec-6][0;39m [36mo.c.b.s.b.e.t.ProcessFlowController [0;39m [2m:[0;39m Application approved: false with comments: This does not deserve to be published
[2m2019-11-25 13:28:09.387[0;39m [32m INFO[0;39m [35m18188[0;39m [2m---[0;39m [2m[nio-8080-exec-6][0;39m [36mo.c.b.s.b.e.t.ProcessFlowController [0;39m [2m:[0;39m Instance from the query: f53c1e54-0fb0-11ea-b813-00155d0a5b14
Hi!
Unfortunately your tweet has been rejected.
Original content: This is the message to be twitted
Comment: This does not deserve to be published
Sorry, please try with better content the next time :-)
As an experiment, if I start several (2) instances of the process:
the review endpoint starts throwing the following exception:
org.camunda.bpm.engine.ProcessEngineException: Query return 2 results instead of max 1
at org.camunda.bpm.engine.impl.AbstractQuery.executeSingleResult(AbstractQuery.java:216) ~[camunda-engine-7.11.0.jar:7.11.0]
at org.camunda.bpm.engine.impl.AbstractQuery.execute(AbstractQuery.java:170) ~[camunda-engine-7.11.0.jar:7.11.0]
at org.camunda.bpm.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:28) ~[camunda-engine-7.11.0.jar:7.11.0]
at org.camunda.bpm.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:107) ~[camunda-engine-7.11.0.jar:7.11.0]
at org.camunda.bpm.engine.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:46) ~[camunda-engine-spring-7.11.0.jar:7.11.0]
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:140) ~[spring-tx-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.camunda.bpm.engine.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:44) ~[camunda-engine-spring-7.11.0.jar:7.11.0]
at org.camunda.bpm.engine.impl.interceptor.ProcessApplicationContextInterceptor.execute(ProcessApplicationContextInterceptor.java:70) ~[camunda-engine-7.11.0.jar:7.11.0]
at org.camunda.bpm.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:33) ~[camunda-engine-7.11.0.jar:7.11.0]
at org.camunda.bpm.engine.impl.AbstractQuery.singleResult(AbstractQuery.java:133) ~[camunda-engine-7.11.0.jar:7.11.0]
at org.camunda.bpm.spring.boot.example.twitter.ProcessFlowController.reviewTweet(ProcessFlowController.java:61) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_231]
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_231]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_231]
at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_231]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200) ~[tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:836) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1747) [tomcat-embed-core-9.0.19.jar:9.0.19]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.19.jar:9.0.19]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_231]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_231]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.19.jar:9.0.19]
at java.lang.Thread.run(Unknown Source) [na:1.8.0_231]
Then, when one of the 2 processes is transitioned to its end via the Task List app, the token count on the user task gets decreased from 2 to 1, but does not get decreased from 1 to 0 (as expected) by the subsequent invocation of the \review endpoint, like before.
My questions are:
Why does the token disappear in the invocation of the original Camunda example code but remains visible in the Cockpit even after the successful process completion when the user task is invoked via an endpoint as described above? Does transitioning user state via code not affect Cockpit view and some extra code manipulations required to sync them up?
Why am I seeing the above exception in the original code? Does it affect anything? Why is it not being thrown when the process invoked via an `/invoke' endpoint?
What needs to be changed in the code behind the /review endpoint to eliminate the Query returns 2 results instead of max 1 exception?

Answer 1

I can start by trying to answer (2): The task was completed and the process completed normally. If you now reload the Browser window with the tasklist, it again tries to open the task with the given id ... but it does not exist anymore, you completed it before. So this is not an exception thrown by the process flow itself but just indicating an invalid state (trying to load something that isn't there).
For (1): Your approach to modify the process instance execution instead of using the taskService#completeTask API is pretty unusual ... you should not use that API for regular process execution, it is meant for migration and administration/repair.
I suppose what you see is that you have two tokens ... the original one still waits at the user task, your additionally created token started after the user task and completed the process, but since there is still a token waiting, the instance remains active. If you use the modification API (which you shouldn't imho) cancel the existing token while creating the modification.
For (3): given that my guess for (1) is correct, that is exactly what happens: you did not cancel the original token, so by using the modification API you created a second one, leading to the "correct" query result.