Correct Error Handling in Spring Statemachine

Question

I am evaluating Spring Statemachine and would like to understand how to recover from a transition error.

I defined an error action for an action executed during a transition. The execution of S1_TO_S2_ACTION causes an exception which is handled in S1_TO_S2_ERROR_HANDLING.

I can handle the error in the action but how can I recover from the error? I tried to send an event in the error handler (context.getStateMachine().sendEvent(Events.RECOVER)) but without any effect.

@Configuration
@EnableStateMachine
class StateMachineConfig
    extends EnumStateMachineConfigurerAdapter<States, Events> {

    Action<States, Events> S1_TO_S2_ERROR_HANDLING = context -> {
        System.out.println(BO + " ERROR!!!");

        System.out.println("E: " + context.getException());
        System.out.println("S: " + context.getSource().getId());
        System.out.println("T: " + context.getTarget().getId());
    };


    @Override
    public void configure(StateMachineTransitionConfigurer<States, Events> transitions)
        throws Exception {

        transitions
        .withExternal()
        .source(States.SI).target(States.S1).event(Events.E1)
        .action(TRANS_ACTION)
        .and()

        .withExternal()            
        .source(States.S1).target(States.S2).event(Events.E2)
        .action(S1_TO_S2_ACTION, S1_TO_S2_ERROR_HANDLING)
        .and()

        .withExternal()
        .source(States.S2).target(States.SE).event(Events.E3)
        .action(TRANS_ACTION);
    }
}

Suprisingly calling stateMachine.hasStateMachineError() afterwards returns false.

Who can I recover in an error action from an error and why does hasStateMachineError() returns false if an exception is thrown during a transition?

Answer 1

I reckon, you need to explicitly do:

try
    {
        ..
    }
    catch (WhateverException e)
    {
        stateMachine.setStateMachineError(e);
        throw e;
    }

Inside the statemachine transition functions.

I posted an answer to a different question, which may be relevant to you as well: https://stackoverflow.com/a/46519081/1258249