本文节选自《设计模式就该这样学》
1 状态模式的UML类图
状态模式的UML类图如下图所示。
2 应用状态模式实现登录状态自在切换
当咱们在社区阅读文章时，如果感觉文章写得很好，咱们就会评论、珍藏两连发。如果处于登录状况下，则能够间接做评论、珍藏这些行为。否则，跳转到登录界面，登录后再继续执行先前的动作。这里波及的状态有两种：登录与未登录；行为有两种：评论和珍藏。上面应用状态模式来实现这个逻辑，代码如下。
首先创立形象状态角色UserState类。
public abstract class UserState { protected AppContext context; public void setContext(AppContext context) { this.context = context; } public abstract void favorite(); public abstract void comment(String comment);}而后创立登录状态LogInState类。
public class LoginInState extends UserState { @Override public void favorite() { System.out.println("珍藏胜利！"); } @Override public void comment(String comment) { System.out.println(comment); }}创立未登录状态UnloginState类。
public class UnLoginState extends UserState { @Override public void favorite() { this.switch2Login(); this.context.getState().favorite(); } @Override public void comment(String comment) { this.switch2Login(); this.context.getState().comment(comment); } private void switch2Login() { System.out.println("跳转到登录页面!"); this.context.setState(this.context.STATE_LOGIN); }}创立上下文角色AppContext类。
public class AppContext { public static final UserState STATE_LOGIN = new LoginInState(); public static final UserState STATE_UNLOGIN = new UnLoginState(); private UserState currentState = STATE_UNLOGIN; { STATE_LOGIN.setContext(this); STATE_UNLOGIN.setContext(this); } public void setState(UserState state) { this.currentState = state; this.currentState.setContext(this); } public UserState getState() { return this.currentState; } public void favorite() { this.currentState.favorite(); } public void comment(String comment) { this.currentState.comment(comment); }}最初编写客户端测试代码。
public static void main(String[] args) { AppContext context = new AppContext(); context.favorite(); context.comment("评论: 好文章，360个赞!");}运行后果如下图所示。
3 应用状态机实现订单状态流转管制
状态机是状态模式的一种利用，相当于上下文角色的一个升级版。在工作流或游戏等各种零碎中有大量应用，如各种工作流引擎，它简直是状态机的子集和实现，封装状态的变动规定。Spring也提供了一个很好的解决方案。Spring中的组件名称就叫作状态机（StateMachine）。状态机帮忙开发者简化状态管制的开发过程，让状态机构造更加层次化。上面用Spring状态机模仿一个订单状态流转的过程。
3.1 增加依赖。
<dependency> <groupId>org.springframework.statemachine</groupId> <artifactId>spring-statemachine-core</artifactId> <version>2.0.1.RELEASE</version></dependency>3.2 创立订单实体Order类。
public class Order { private int id; private OrderStatus status; public void setStatus(OrderStatus status) { this.status = status; } public OrderStatus getStatus() { return status; } public void setId(int id) { this.id = id; } public int getId() { return id; } @Override public String toString() { return "订单号：" + id + ", 订单状态：" + status; }}3.3 创立订单状态枚举类和状态转换枚举类。
/** * 订单状态 */public enum OrderStatus { //待领取，待发货，待收货，订单完结 WAIT_PAYMENT, WAIT_DELIVER, WAIT_RECEIVE, FINISH;}/** * 订单状态扭转事件 */public enum OrderStatusChangeEvent { //领取，发货，确认收货 PAYED, DELIVERY, RECEIVED;}3.4 增加状态流转配置。
/** * 订单状态机配置 */@Configuration@EnableStateMachine(name = "orderStateMachine")public class OrderStateMachineConfig extends StateMachineConfigurerAdapter<OrderStatus, OrderStatusChangeEvent> { /** * 配置状态 * @param states * @throws Exception */ public void configure(StateMachineStateConfigurer<OrderStatus, OrderStatusChangeEvent> states) throws Exception { states .withStates() .initial(OrderStatus.WAIT_PAYMENT) .states(EnumSet.allOf(OrderStatus.class)); } /** * 配置状态转换事件关系 * @param transitions * @throws Exception */ public void configure(StateMachineTransitionConfigurer<OrderStatus, OrderStatusChangeEvent> transitions) throws Exception { transitions .withExternal().source(OrderStatus.WAIT_PAYMENT).target(OrderStatus.WAIT_DELIVER) .event(OrderStatusChangeEvent.PAYED) .and() .withExternal().source(OrderStatus.WAIT_DELIVER).target(OrderStatus.WAIT_RECEIVE) .event(OrderStatusChangeEvent.DELIVERY) .and() .withExternal().source(OrderStatus.WAIT_RECEIVE).target(OrderStatus.FINISH) .event(OrderStatusChangeEvent.RECEIVED); } /** * 长久化配置 * 在理论应用中，能够配合Redis等进行长久化操作 * @return */ @Bean public DefaultStateMachinePersister persister(){ return new DefaultStateMachinePersister<>(new StateMachinePersist<Object, Object, Order>() { @Override public void write(StateMachineContext<Object, Object> context, Order order) throws Exception { //此处并没有进行长久化操作 } @Override public StateMachineContext<Object, Object> read(Order order) throws Exception { //此处间接获取Order中的状态，其实并没有进行长久化读取操作 return new DefaultStateMachineContext(order.getStatus(), null, null, null); } }); }}3.5 增加订单状态监听器。
@Component("orderStateListener")@WithStateMachine(name = "orderStateMachine")public class OrderStateListenerImpl{ @OnTransition(source = "WAIT_PAYMENT", target = "WAIT_DELIVER") public boolean payTransition(Message<OrderStatusChangeEvent> message) { Order order = (Order) message.getHeaders().get("order"); order.setStatus(OrderStatus.WAIT_DELIVER); System.out.println("领取，状态机反馈信息：" + message.getHeaders().toString()); return true; } @OnTransition(source = "WAIT_DELIVER", target = "WAIT_RECEIVE") public boolean deliverTransition(Message<OrderStatusChangeEvent> message) { Order order = (Order) message.getHeaders().get("order"); order.setStatus(OrderStatus.WAIT_RECEIVE); System.out.println("发货，状态机反馈信息：" + message.getHeaders().toString()); return true; } @OnTransition(source = "WAIT_RECEIVE", target = "FINISH") public boolean receiveTransition(Message<OrderStatusChangeEvent> message){ Order order = (Order) message.getHeaders().get("order"); order.setStatus(OrderStatus.FINISH); System.out.println("收货，状态机反馈信息：" + message.getHeaders().toString()); return true; }}3.6 创立IOrderService接口。
public interface IOrderService { //创立新订单 Order create(); //发动领取 Order pay(int id); //订单发货 Order deliver(int id); //订单收货 Order receive(int id); //获取所有订单信息 Map<Integer, Order> getOrders();}3.7 在Service业务逻辑中利用。
@Service("orderService")public class OrderServiceImpl implements IOrderService { @Autowired private StateMachine<OrderStatus, OrderStatusChangeEvent> orderStateMachine; @Autowired private StateMachinePersister<OrderStatus, OrderStatusChangeEvent, Order> persister; private int id = 1; private Map<Integer, Order> orders = new HashMap<>(); public Order create() { Order order = new Order(); order.setStatus(OrderStatus.WAIT_PAYMENT); order.setId(id++); orders.put(order.getId(), order); return order; } public Order pay(int id) { Order order = orders.get(id); System.out.println("线程名称：" + Thread.currentThread().getName() + " 尝试领取，订单号：" + id); Message message = MessageBuilder.withPayload(OrderStatusChangeEvent.PAYED).setHeader("order", order).build(); if (!sendEvent(message, order)) { System.out.println("线程名称：" + Thread.currentThread().getName() + " 领取失败, 状态异样，订单号：" + id); } return orders.get(id); } public Order deliver(int id) { Order order = orders.get(id); System.out.println("线程名称：" + Thread.currentThread().getName() + " 尝试发货，订单号：" + id); if (!sendEvent(MessageBuilder.withPayload(OrderStatusChangeEvent.DELIVERY).setHeader("order", order).build(), orders.get(id))) { System.out.println("线程名称：" + Thread.currentThread().getName() + " 发货失败，状态异样，订单号：" + id); } return orders.get(id); } public Order receive(int id) { Order order = orders.get(id); System.out.println("线程名称：" + Thread.currentThread().getName() + " 尝试收货，订单号：" + id); if (!sendEvent(MessageBuilder.withPayload(OrderStatusChangeEvent.RECEIVED).setHeader("order", order).build(), orders.get(id))) { System.out.println("线程名称：" + Thread.currentThread().getName() + " 收货失败，状态异样，订单号：" + id); } return orders.get(id); } public Map<Integer, Order> getOrders() { return orders; } /** * 发送订单状态转换事件 * * @param message * @param order * @return */ private synchronized boolean sendEvent(Message<OrderStatusChangeEvent> message, Order order) { boolean result = false; try { orderStateMachine.start(); //尝试复原状态机状态 persister.restore(orderStateMachine, order); //增加提早用于线程平安测试 Thread.sleep(1000); result = orderStateMachine.sendEvent(message); //长久化状态机状态 persister.persist(orderStateMachine, order); } catch (Exception e) { e.printStackTrace(); } finally { orderStateMachine.stop(); } return result; }}3.8 编写客户端测试代码。
@SpringBootApplicationpublic class Test { public static void main(String[] args) { Thread.currentThread().setName("主线程"); ConfigurableApplicationContext context = SpringApplication.run(Test.class,args); IOrderService orderService = (IOrderService)context.getBean("orderService"); orderService.create(); orderService.create(); orderService.pay(1); new Thread("客户线程"){ @Override public void run() { orderService.deliver(1); orderService.receive(1); } }.start(); orderService.pay(2); orderService.deliver(2); orderService.receive(2); System.out.println("全副订单状态：" + orderService.getOrders()); }}通过这个实在的业务案例，置信小伙伴们曾经对状态模式有了一个十分粗浅的了解。
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