camunda exception Cannot find task with id task is null

Question

First I'd like to say that I've seen this question: camunda Cannot find task with id task is null and that question is just not my issue here.

I've built a rest api using jersey and I'm using camunda workflow engine.

I've used jersey-quickstart-grizzly maven archtype and then defined Process resource like this :

@Path("process")
public class Process {

/**
 * Method handling HTTP GET requests. The returned object will be sent
 * to the client as "text/plain" media type.
 *
 */
@POST
@Produces(MediaType.APPLICATION_JSON)
@Path("start")
public void start(){
    ProcessEngineManager.getEngine().getRuntimeService().startProcessInstanceByKey("test");
}

@POST
@Produces(MediaType.APPLICATION_JSON)
@Path("next")
public void next(@FormParam("name") String name){
    Map formParams = new HashMap<>();
    formParams.put("name",name);
    ProcessEngineManager.getEngine().getFormService().submitTaskForm("testtask",formParams);
}
}

and this is ProcessEngineManager.java :

import org.camunda.bpm.engine.ProcessEngine;
import org.camunda.bpm.engine.ProcessEngines;

public class ProcessEngineManager {
    private static ProcessEngine engine;
    public static ProcessEngine getEngine(){
        if(engine==null) {
            engine = ProcessEngines.getDefaultProcessEngine();
            engine.getRepositoryService().createDeployment()
                    .addClasspathResource("workflowtest/test.bpmn")
                    .deploy();
        }
        return engine;
    }
}

I have test.bpmn under src/main/resources/workflowtest defined like this:

In Xml :



  
    
      SequenceFlow_1v6clcy
    
    
    
      
        
          
        
      
      SequenceFlow_1v6clcy
      SequenceFlow_07kdfp4
    
    
      SequenceFlow_07kdfp4

I have camunda.cfg.xml under src/main/resources defined like this :

I'm testing my api using curl, I verified that curl -X POST http://localhost:8080/process/start works and a process is started, after that I do curl -X POST -d '{name: "John"}' http://localhost:8080/process/next and I see this exception in server console:

org.camunda.bpm.engine.exception.NullValueException: Cannot find task with id testtask: task is null at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:1.8.0_151] at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[?:1.8.0_151] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[?:1.8.0_151] at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[?:1.8.0_151] at org.camunda.bpm.engine.impl.util.EnsureUtil.generateException(EnsureUtil.java:344) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.util.EnsureUtil.ensureNotNull(EnsureUtil.java:49) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.util.EnsureUtil.ensureNotNull(EnsureUtil.java:44) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.cmd.SubmitTaskFormCmd.execute(SubmitTaskFormCmd.java:54) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:24) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:104) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.interceptor.ProcessApplicationContextInterceptor.execute(ProcessApplicationContextInterceptor.java:66) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:30) ~[camunda-engine-7.8.0.jar:7.8.0] at org.camunda.bpm.engine.impl.FormServiceImpl.submitTaskForm(FormServiceImpl.java:88) ~[camunda-engine-7.8.0.jar:7.8.0] at workflowtest.Process.next(Process.java:37) ~[classes/:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_151] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_151] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_151] at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_151] at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:76) ~[jersey-server-2.26.jar:?] at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:148) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:191) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$VoidOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:183) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:103) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:493) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:415) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:104) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:277) [jersey-server-2.26.jar:?] at org.glassfish.jersey.internal.Errors$1.call(Errors.java:272) [jersey-common-2.26.jar:?] at org.glassfish.jersey.internal.Errors$1.call(Errors.java:268) [jersey-common-2.26.jar:?] at org.glassfish.jersey.internal.Errors.process(Errors.java:316) [jersey-common-2.26.jar:?] at org.glassfish.jersey.internal.Errors.process(Errors.java:298) [jersey-common-2.26.jar:?] at org.glassfish.jersey.internal.Errors.process(Errors.java:268) [jersey-common-2.26.jar:?] at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:289) [jersey-common-2.26.jar:?] at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:256) [jersey-server-2.26.jar:?] at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:703) [jersey-server-2.26.jar:?] at org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainer.service(GrizzlyHttpContainer.java:377) [jersey-container-grizzly2-http-2.26.jar:?] at org.glassfish.grizzly.http.server.HttpHandler$1.run(HttpHandler.java:224) [grizzly-http-server-2.4.0.jar:2.4.0] at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:593) [grizzly-framework-2.4.0.jar:2.4.0] at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:573) [grizzly-framework-2.4.0.jar:2.4.0] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_151]

I don't understand why ? it does start the process so it finds process "test" but not task "testtask", why is that and how to solve the issue ?

Big Goal

This project is just a test of an idea for a workflow management system we'd like to build, the idea we want to test is that we can build the form our own way getting its options for select input from our own database and still use camunda as workflow engine.

thorben · Accepted Answer

testTask is the id of the user task in the process but not the id of the task Camunda creates at runtime when execution flow reaches the activity. You can obtain tasks via TaskService#createTaskQuery. This should return one result in your example. Then get the ID via Task#getId and use that as the parameter for calling FormService#submitTaskForm.

Why is that so? You can have more then one instance of a process and therefore more than one instance per BPMN activity. Then, the activity ID cannot uniquely identify a single task instance.

Why does starting the process instance with test work when test is the ID in the process model? This is called in Camunda terms the process key and when you start a process instance that way, it always refers to the latest version of a process definition with that key.

camunda exception Cannot find task with id task is null

Big Goal

Answers (1)

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