Spring Statemachine - Quick Reference

Full Reference: See advanced.md for @WithStateMachine annotation, hierarchical states, choice pseudostates, timer transitions, listeners, persistence, and testing.

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: spring-statemachine for comprehensive documentation.

Dependencies

<!-- Spring Statemachine 4.0+ for Spring Boot 3.x -->
<dependency>
    <groupId>org.springframework.statemachine</groupId>
    <artifactId>spring-statemachine-starter</artifactId>
    <version>4.0.0</version>
</dependency>
<!-- For persistence -->
<dependency>
    <groupId>org.springframework.statemachine</groupId>
    <artifactId>spring-statemachine-data-jpa</artifactId>
    <version>4.0.0</version>
</dependency>

Core Concepts

┌─────────────────────────────────────────────────────────────┐
│                    State Machine                            │
│                                                             │
│  ┌──────────┐    EVENT_A     ┌──────────┐                  │
│  │  STATE_1 │ ─────────────▶ │  STATE_2 │                  │
│  │ (initial)│                │          │                  │
│  └──────────┘                └────┬─────┘                  │
│                                   │                         │
│                              EVENT_B                        │
│                                   │                         │
│                                   ▼                         │
│                             ┌──────────┐                    │
│                             │  STATE_3 │                    │
│                             │  (final) │                    │
│                             └──────────┘                    │
└─────────────────────────────────────────────────────────────┘

Basic Configuration

States and Events

public enum OrderStates {
    CREATED,
    PENDING_PAYMENT,
    PAID,
    PROCESSING,
    SHIPPED,
    DELIVERED,
    CANCELLED,
    REFUNDED
}

public enum OrderEvents {
    SUBMIT,
    PAY,
    PROCESS,
    SHIP,
    DELIVER,
    CANCEL,
    REFUND
}

State Machine Configuration

@Configuration
@EnableStateMachineFactory
public class OrderStateMachineConfig
        extends EnumStateMachineConfigurerAdapter<OrderStates, OrderEvents> {

    @Override
    public void configure(StateMachineStateConfigurer<OrderStates, OrderEvents> states)
            throws Exception {
        states
            .withStates()
                .initial(OrderStates.CREATED)
                .state(OrderStates.PENDING_PAYMENT)
                .state(OrderStates.PAID)
                .state(OrderStates.PROCESSING)
                .state(OrderStates.SHIPPED)
                .end(OrderStates.DELIVERED)
                .end(OrderStates.CANCELLED)
                .end(OrderStates.REFUNDED);
    }

    @Override
    public void configure(StateMachineTransitionConfigurer<OrderStates, OrderEvents> transitions)
            throws Exception {
        transitions
            .withExternal()
                .source(OrderStates.CREATED)
                .target(OrderStates.PENDING_PAYMENT)
                .event(OrderEvents.SUBMIT)
            .and()
            .withExternal()
                .source(OrderStates.PENDING_PAYMENT)
                .target(OrderStates.PAID)
                .event(OrderEvents.PAY)
                .guard(paymentValidGuard())
                .action(paymentAction())
            .and()
            .withExternal()
                .source(OrderStates.PAID)
                .target(OrderStates.PROCESSING)
                .event(OrderEvents.PROCESS)
            .and()
            .withExternal()
                .source(OrderStates.PROCESSING)
                .target(OrderStates.SHIPPED)
                .event(OrderEvents.SHIP)
                .action(shipAction())
            .and()
            .withExternal()
                .source(OrderStates.SHIPPED)
                .target(OrderStates.DELIVERED)
                .event(OrderEvents.DELIVER)
            .and()
            // Cancel from multiple states
            .withExternal()
                .source(OrderStates.CREATED)
                .target(OrderStates.CANCELLED)
                .event(OrderEvents.CANCEL)
            .and()
            .withExternal()
                .source(OrderStates.PENDING_PAYMENT)
                .target(OrderStates.CANCELLED)
                .event(OrderEvents.CANCEL);
    }
}

Guards and Actions

Guards (Conditions)

@Configuration
public class OrderGuards {

    @Bean
    public Guard<OrderStates, OrderEvents> paymentValidGuard() {
        return context -> {
            Order order = (Order) context.getExtendedState()
                .getVariables().get("order");
            PaymentInfo payment = (PaymentInfo) context.getMessage()
                .getHeaders().get("payment");

            return payment != null &&
                   payment.getAmount().compareTo(order.getTotal()) >= 0;
        };
    }

    @Bean
    public Guard<OrderStates, OrderEvents> refundEligibleGuard() {
        return context -> {
            Order order = (Order) context.getExtendedState()
                .getVariables().get("order");
            LocalDateTime deliveredAt = order.getDeliveredAt();

            // Refund within 30 days
            return deliveredAt != null &&
                   deliveredAt.plusDays(30).isAfter(LocalDateTime.now());
        };
    }
}

Actions

@Configuration
public class OrderActions {

    @Bean
    public Action<OrderStates, OrderEvents> paymentAction() {
        return context -> {
            Order order = (Order) context.getExtendedState()
                .getVariables().get("order");
            PaymentInfo payment = (PaymentInfo) context.getMessage()
                .getHeaders().get("payment");

            order.setPaymentId(payment.getTransactionId());
            order.setPaidAt(LocalDateTime.now());
            orderRepository.save(order);

            log.info("Payment processed for order: {}", order.getId());
        };
    }

    @Bean
    public Action<OrderStates, OrderEvents> shipAction() {
        return context -> {
            Order order = (Order) context.getExtendedState()
                .getVariables().get("order");

            String trackingNumber = shippingService.createShipment(order);
            order.setTrackingNumber(trackingNumber);
            order.setShippedAt(LocalDateTime.now());
            orderRepository.save(order);

            notificationService.sendShippingNotification(order);
        };
    }

    // Error action
    @Bean
    public Action<OrderStates, OrderEvents> errorAction() {
        return context -> {
            Exception exception = context.getException();
            log.error("State machine error: {}", exception.getMessage());
        };
    }
}

State Machine Service

@Service
@RequiredArgsConstructor
@Slf4j
public class OrderStateMachineService {

    private final StateMachineFactory<OrderStates, OrderEvents> factory;
    private final OrderRepository orderRepository;

    public void processEvent(Long orderId, OrderEvents event, Map<String, Object> headers) {
        Order order = orderRepository.findById(orderId)
            .orElseThrow(() -> new OrderNotFoundException(orderId));

        StateMachine<OrderStates, OrderEvents> sm = build(order);

        Message<OrderEvents> message = MessageBuilder
            .withPayload(event)
            .copyHeaders(headers)
            .setHeader("orderId", orderId)
            .build();

        // Reactive event sending (Spring Statemachine 4.0+)
        sm.sendEvent(Mono.just(message))
            .doOnComplete(() -> log.info("Event {} processed for order {}", event, orderId))
            .doOnError(e -> log.error("Error processing event: {}", e.getMessage()))
            .subscribe();
    }

    private StateMachine<OrderStates, OrderEvents> build(Order order) {
        StateMachine<OrderStates, OrderEvents> sm = factory.getStateMachine(
            order.getId().toString()
        );

        sm.stopReactively().block();

        sm.getStateMachineAccessor()
            .doWithAllRegions(accessor -> {
                accessor.resetStateMachineReactively(
                    new DefaultStateMachineContext<>(
                        order.getState(), null, null, null
                    )
                ).block();
            });

        sm.getExtendedState().getVariables().put("order", order);
        sm.startReactively().block();

        return sm;
    }

    public boolean canTransition(Long orderId, OrderEvents event) {
        Order order = orderRepository.findById(orderId).orElseThrow();
        StateMachine<OrderStates, OrderEvents> sm = build(order);

        return sm.getTransitions().stream()
            .anyMatch(t -> t.getSource().getId() == order.getState() &&
                          t.getTrigger().getEvent() == event);
    }
}

Best Practices

Do	Don't
Define clear states and events	Use generic state names
Use guards for validation	Put business logic in transitions
Persist state machine state	Keep state only in memory
Handle all edge cases	Assume happy path only
Use listeners for monitoring	Ignore state changes

Production Checklist

When NOT to Use This Skill

Simple status fields - Use enum with database column
Complex orchestration - Use Spring Integration or Camunda BPM
Business rules - Use Drools or similar rules engine
Event-driven sagas - Consider Spring Cloud Stream

Anti-Patterns

Anti-Pattern	Problem	Solution
State in memory only	Lost on restart	Use JPA persistence
Complex logic in guards	Hard to test	Extract to services
Missing error actions	Silent failures	Add error handling actions
Single machine instance	Concurrency issues	Use factory pattern
No state validation	Invalid transitions	Implement guards properly

Quick Troubleshooting

Problem	Diagnostic	Fix
Event not accepted	Check current state	Verify transition exists
Guard always false	Debug guard logic	Log guard evaluation
Action not executed	Check transition config	Verify action is attached
State not persisted	Check persister config	Configure JPA persister
Machine not starting	Check initial state	Verify initial() configured

Reference Documentation

Spring Statemachine Reference