如何使用状态机较好的实现订单状态流转？

订单状态枚举类与订单事件枚举类

public enum OrderStates {CREATED, PAID, SHIPPED, DELIVERED
}public enum OrderEvents {PAY, SHIP, DELIVER
}

方式一：使用Spring有状态状态机实现

OrderStateMachine 类

@Component
public class OrderStateMachine {private static StateMachine<OrderStates, OrderEvents> stateMachine() throws Exception {StateMachineBuilder.Builder<OrderStates, OrderEvents> builder = StateMachineBuilder.builder();builder.configureStates().withStates().initial(OrderStates.CREATED).states(EnumSet.allOf(OrderStates.class));builder.configureTransitions().withExternal().source(OrderStates.CREATED).target(OrderStates.PAID).event(OrderEvents.PAY).and().withExternal().source(OrderStates.PAID).target(OrderStates.SHIPPED).event(OrderEvents.SHIP).and().withExternal().source(OrderStates.SHIPPED).target(OrderStates.DELIVERED).event(OrderEvents.DELIVER);return builder.build();}public StateMachine<OrderStates, OrderEvents> create(OrderStates state) throws Exception {StateMachine<OrderStates, OrderEvents> stateMachine = stateMachine();stateMachine.stop();// 恢复状态机的状态StateMachineContext<OrderStates, OrderEvents> context = new DefaultStateMachineContext<>(state, null, null, null);stateMachine.getStateMachineAccessor().doWithAllRegions(access -> access.resetStateMachine(context));stateMachine.start();return stateMachine;}
}

OrderService 类

@Service
public class OrderService {@Autowiredprivate OrderStateMachine orderStateMachine;public void processOrderEvent(String orderId, OrderEvents event) throws Exception {// 使用Spring有状态状态机StateMachine<OrderStates, OrderEvents> state = orderStateMachine.create(OrderStates.CREATED);boolean success = state.sendEvent(event);if (success) {OrderStates newState = state.getState().getId();// 更新数据库或其他存储中的订单状态为newState} else {// 处理发送事件失败的情况}}
}

方式二：使用无状态状态机实现

StatelessOrderStateMachine 类

@Component
public class StatelessOrderStateMachine {public OrderStates handleEvent(OrderStates currentState, OrderEvents event) {switch (currentState) {case CREATED:if (event == OrderEvents.PAY) {return OrderStates.PAID;}break;case PAID:if (event == OrderEvents.SHIP) {return OrderStates.SHIPPED;}break;case SHIPPED:if (event == OrderEvents.DELIVER) {return OrderStates.DELIVERED;}break;default:throw new IllegalStateException("Unexpected state: " + currentState);}throw new IllegalArgumentException("Cannot handle event " + event + " in state " + currentState);}
}

OrderService 类

@Service
public class OrderService {@Autowiredprivate StatelessOrderStateMachine statelessOrderStateMachine;public void processOrderEvent(String orderId, OrderEvents event) {// 使用无状态状态机try {OrderStates newState = statelessOrderStateMachine.handleEvent(OrderStates.CREATED, event);// 更新数据库或其他存储中的订单状态为newState} catch (IllegalStateException e) {// 处理非法状态转换的情况}}
}

总结

• 方式一（有状态状态机）：适合处理复杂状态流转，功能强大，但实现较为复杂。
• 方式二（无状态状态机）：简单易用，适合处理简单状态流转，且天然线程安全。