Not able to catch and rethrow spring state machine error

[ArpanMajumdar]

I am working on a project that deals with a contract workflow. I want the state machine to throw an error if a wrong event is sent. I tried using listener to catch the exception thrown by state machine as given in the documentation but I am not able to rethrow error to show an exception message.

Here is my listener

public class ErrorStateMachineListener
    extends StateMachineListenerAdapter<AgreementSubStatus, AgreementEvents> {

  @Override
  public void stateMachineError(
      StateMachine<AgreementSubStatus, AgreementEvents> stateMachine, Exception exception) {
    log.error("Access is denied. Illegal state transition");
    throw new AccessDeniedException("Access is denied");
  }

@Override
  public void eventNotAccepted(Message<AgreementEvents> event) {
    log.info("Inside eventNotAccepted");
    throw new AccessDeniedException("Access is denied");
  }
}

Here is the state machine configuration where I registered the listener.

    // Configure state machine
    builder
        .configureConfiguration()
        .withConfiguration()
        .autoStartup(true)
        .listener(listener())
        .and()
        .withSecurity()
        .enabled(true);

Here is the stack trace obtained after throwing custom exception from the listener.

com.tgt.tvi.libs.basesecurity.exception.AccessDeniedException: Access is denied
	at com.tgt.tvi.apis.agreement.statemachine.ErrorStateMachineListener.eventNotAccepted(ErrorStateMachineListener.java:59)
	at org.springframework.statemachine.listener.CompositeStateMachineListener.eventNotAccepted(CompositeStateMachineListener.java:82)
	at org.springframework.statemachine.support.StateMachineObjectSupport.notifyEventNotAccepted(StateMachineObjectSupport.java:193)
	at org.springframework.statemachine.support.AbstractStateMachine.notifyEventNotAccepted(AbstractStateMachine.java:224)
	at org.springframework.statemachine.support.AbstractStateMachine.sendEventInternal(AbstractStateMachine.java:606)
	at org.springframework.statemachine.support.AbstractStateMachine.sendEvent(AbstractStateMachine.java:218)
	at org.springframework.statemachine.support.AbstractStateMachine.sendEvent(AbstractStateMachine.java:230)

I've also tried putting a try-catch block around sendEvent method but it doesn't come inside the catch block.

try{
        stateMachine.sendEvent(action);
      }catch (Exception e){
        log.error("State machine exception");
   }

Please tell what approach should I take to catch state machine errors to rethrow them and perform some logic.

[jvalkeal]

None of these would not work as any user level interaction cannot break machine. Can't you just check from StateMachine.sendEvent() if it returns false and then throw exception of your own. But do remember that depending on your machine structure, even if event is accepted, in theoretical level it doesn't necessarily mean that machine is actually going to do any state changes.

[CodeYogiCo]

@jvalkeal one unusal behaviour on similar lines. I have spring security configured. And my transition has security enabled. If a wrong role tries to do a transition , it logs AccessDeniedException.However it does not throw that exception

 transitions
        // When initially agreement lifecycle is started
        .withExternal()
        .source(AgreementSubStatus.S1)
        .target(AgreementSubStatus.S2)
        .event(AgreementEvents.CREATED)
        .action(this.S1toS2(),errorAction())
        .secured(IS_ADMIN_OR_BUYER_OR_FINOPS_OR_SUPPORT)

This is the exception being thrown

org.springframework.security.access.AccessDeniedException: Access is denied
	at org.springframework.security.access.vote.AffirmativeBased.decide(AffirmativeBased.java:84)
	at org.springframework.statemachine.security.StateMachineSecurityInterceptor.decide(StateMachineSecurityInterceptor.java:190)
	at org.springframework.statemachine.security.StateMachineSecurityInterceptor.decide(StateMachineSecurityInterceptor.java:157)
	at org.springframework.statemachine.security.StateMachineSecurityInterceptor.preTransition(StateMachineSecurityInterceptor.java:109)
	at org.springframework.statemachine.support.StateMachineInterceptorList.preTransition(StateMachineInterceptorList.java:128)
	at org.springframework.statemachine.support.DefaultStateMachineExecutor.handleTriggerTrans(DefaultStateMachineExecutor.java:266)
	at org.springframework.statemachine.support.DefaultStateMachineExecutor.handleTriggerTrans(DefaultStateMachineExecutor.java:211)
	at org.springframework.statemachine.support.DefaultStateMachineExecutor.processTriggerQueue(DefaultStateMachineExecutor.java:449)
	at org.springframework.statemachine.support.DefaultStateMachineExecutor.access$200(DefaultStateMachineExecutor.java:65)
	at org.springframework.statemachine.support.DefaultStateMachineExecutor$1.run(DefaultStateMachineExecutor.java:323)
	at org.springframework.core.task.SyncTaskExecutor.execute(SyncTaskExecutor.java:50)
	at org.springframework.statemachine.support.DefaultStateMachineExecutor.scheduleEventQueueProcessing(DefaultStateMachineExecutor.java:352)
	at org.springframework.statemachine.support.DefaultStateMachineExecutor.execute(DefaultStateMachineExecutor.java:163)
	at org.springframework.statemachine.support.AbstractStateMachine.sendEventInternal(AbstractStateMachine.java:604)
	at org.springframework.statemachine.support.AbstractStateMachine.sendEvent(AbstractStateMachine.java:218)

However i went ahead and looked into the code .Its just logging it but not being thrown

try {
                                stateContext = this.interceptors.preTransition(stateContext);
                            } catch (Exception var16) {
                                log.info("Interceptors threw exception", var16);
                                stateContext = null;
                            }

Can you help me how can i handle such scenraiors

[jvalkeal]

Well security integration is designed to work internally effectively denying transitions. In this case it breaks from a loop if you follow logic around those lines.

[ArpanMajumdar]

@jvalkeal How do I catch this error if it isn't being rethrown? Should I just check if stateContext is null?

[Bonbons]

Well security integration is designed to work internally effectively denying transitions. In this case it breaks from a loop if you follow logic around those lines.

But, we need to know why transition is denied. The reason is only accessible in the log. We got to indicate to the final user why the machine is still une the same state.

[Bonbons]

@jvalkeal
Ok, but it would be nice to be able to check all error after the loop on transitions.
In this case, it would be interesting to put the AccessDeniedException in a stack. Then, to provide the stack atfer the loop.

[tovisofer]

Hi @jvalkeal,
I saw similar question\bug report mentioned three times.
Is anyone handling it?

#548
#340

[Achilles718611]

We can set statemachine error using machine.setStateMachineError(new ResponseStatusException(HttpStatus.INTERNAL_SERVER_ERROR, "XXX"));
How we can get this error after send event?

i.e machine.sendEvent(event);
When process event, we set stateMachineError, but I don't know how I can retrieve that error later.

[sthallapalliatsmava]

https://stackoverflow.com/questions/55047384/how-to-get-exception-thrown-during-state-transition-using-spring-state-machine