美团的设计模式二三事

// 奖励服务
class RewardService {
    // 外部服务
    private WaimaiService waimaiService;
    private HotelService hotelService;
    private FoodService foodService;
    // 使用对入参的条件判断进行发奖
    public void issueReward(String rewardType, Object ... params) {
        if ("Waimai".equals(rewardType)) {
            WaimaiRequest request = new WaimaiRequest();
            // 构建入参
            request.setWaimaiReq(params);
            waimaiService.issueWaimai(request);
        } else if ("Hotel".equals(rewardType)) {
            HotelRequest request = new HotelRequest();
            request.addHotelReq(params);
            hotelService.sendPrize(request);
        } else if ("Food".equals(rewardType)) {
            FoodRequest request = new FoodRequest(params);
            foodService.getCoupon(request);
        } else {
            throw new IllegalArgumentException("rewardType error!");
        }
    }
}

// 策略接口
interface Strategy {
    void issue(Object ... params);
}
// 外卖策略
class Waimai implements Strategy {
    private WaimaiService waimaiService;
    @Override
    public void issue(Object... params) {
        WaimaiRequest request = new WaimaiRequest();
        // 构建入参
        request.setWaimaiReq(params);
        waimaiService.issueWaimai(request);
    }
}
// 酒旅策略
class Hotel implements Strategy {
    private HotelService hotelService;
    @Override
    public void issue(Object... params) {
        HotelRequest request = new HotelRequest();
        request.addHotelReq(params);
        hotelService.sendPrize(request);
    }
}
// 美食策略
class Food implements Strategy {
    private FoodService foodService;
    @Override
    public void issue(Object... params) {
        FoodRequest request = new FoodRequest(params);
        foodService.payCoupon(request);
    }
}

// 使用分支判断获取的策略上下文
class StrategyContext {
    public static Strategy getStrategy(String rewardType) {
        switch (rewardType) {
            case "Waimai":
                return new Waimai();
            case "Hotel":
                return new Hotel();
            case "Food":
                return new Food();
            default:
                throw new IllegalArgumentException("rewardType error!");
        }
    }
}
// 优化后的策略服务
class RewardService {
    public void issueReward(String rewardType, Object ... params) {
        Strategy strategy = StrategyContext.getStrategy(rewardType);
        strategy.issue(params);
    }
}

// 策略上下文，用于管理策略的注册和获取
class StrategyContext {
    private static final Map<String, Strategy> registerMap = new HashMap<>();
    // 注册策略
    public static void registerStrategy(String rewardType, Strategy strategy) {
        registerMap.putIfAbsent(rewardType, strategy);
    }
    // 获取策略
    public static Strategy getStrategy(String rewardType) {
        return registerMap.get(rewardType);
    }
}
// 抽象策略类
abstract class AbstractStrategy implements Strategy {
    // 类注册方法
    public void register() {
        StrategyContext.registerStrategy(getClass().getSimpleName(), this);
    }
}
// 单例外卖策略
class Waimai extends AbstractStrategy implements Strategy {
    private static final Waimai instance = new Waimai();
    private WaimaiService waimaiService;
    private Waimai() {
        register();
    }
    public static Waimai getInstance() {
        return instance;
    }
    @Override
    public void issue(Object... params) {
        WaimaiRequest request = new WaimaiRequest();
        // 构建入参
        request.setWaimaiReq(params);
        waimaiService.issueWaimai(request);
    }
}
// 单例酒旅策略
class Hotel extends AbstractStrategy implements Strategy {
    private static final Hotel instance = new Hotel();
    private HotelService hotelService;
    private Hotel() {
        register();
    }
    public static Hotel getInstance() {
        return instance;
    }
    @Override
    public void issue(Object... params) {
        HotelRequest request = new HotelRequest();
        request.addHotelReq(params);
        hotelService.sendPrize(request);
    }
}
// 单例美食策略
class Food extends AbstractStrategy implements Strategy {
    private static final Food instance = new Food();
    private FoodService foodService;
    private Food() {
        register();
    }
    public static Food getInstance() {
        return instance;
    }
    @Override
    public void issue(Object... params) {
        FoodRequest request = new FoodRequest(params);
        foodService.payCoupon(request);
    }
}

// 任务状态枚举
@AllArgsConstructor
@Getter
enum TaskState {
    INIT("初始化"),
    ONGOING( "进行中"),
    PAUSED("暂停中"),
    FINISHED("已完成"),
    EXPIRED("已过期")
    ;
    private final String message;
}
// 行为枚举
@AllArgsConstructor
@Getter
enum ActionType {
    START(1, "开始"),
    STOP(2, "暂停"),
    ACHIEVE(3, "完成"),
    EXPIRE(4, "过期")
    ;
    private final int code;
    private final String message;
}

class Task {
    private Long taskId;
    // 任务的默认状态为初始化
    private TaskState state = TaskState.INIT;
    // 活动服务
    private ActivityService activityService;
    // 任务管理器
    private TaskManager taskManager;
    // 使用条件分支进行任务更新
    public void updateState(ActionType actionType) {
        if (state == TaskState.INIT) {
            if (actionType == ActionType.START) {
                state = TaskState.ONGOING;
            }
        } else if (state == TaskState.ONGOING) {
            if (actionType == ActionType.ACHIEVE) {
                state = TaskState.FINISHED;
                // 任务完成后进对外部服务进行通知
                activityService.notifyFinished(taskId);
                taskManager.release(taskId);
            } else if (actionType == ActionType.STOP) {
                state = TaskState.PAUSED;
            } else if (actionType == ActionType.EXPIRE) {
                state = TaskState.EXPIRED;
            }
        } else if (state == TaskState.PAUSED) {
            if (actionType == ActionType.START) {
                state = TaskState.ONGOING;
            } else if (actionType == ActionType.EXPIRE) {
                state = TaskState.EXPIRED;
            }
        }
    }
}

// 任务状态抽象接口
interface State {
    // 默认实现，不做任何处理
    default void update(Task task, ActionType actionType) {
        // do nothing
    }
}
// 任务初始状态
class TaskInit implements State {
    @Override
    public void update(Task task, ActionType actionType) {
        if  (actionType == ActionType.START) {
            task.setState(new TaskOngoing());
        }
    }
}
// 任务进行状态
class TaskOngoing implements State {
    private ActivityService activityService;
    private TaskManager taskManager; 
    @Override
    public void update(Task task, ActionType actionType) {
        if (actionType == ActionType.ACHIEVE) {
            task.setState(new TaskFinished());
            // 通知
            activityService.notifyFinished(taskId);
            taskManager.release(taskId);
        } else if (actionType == ActionType.STOP) {
            task.setState(new TaskPaused());
        } else if (actionType == ActionType.EXPIRE) {
            task.setState(new TaskExpired());
        }
    }
}
// 任务暂停状态
class TaskPaused implements State {
    @Override
    public void update(Task task, ActionType actionType) {
        if (actionType == ActionType.START) {
            task.setState(new TaskOngoing());
        } else if (actionType == ActionType.EXPIRE) {
            task.setState(new TaskExpired());
        }
    }
}
// 任务完成状态
class TaskFinished implements State {
}
// 任务过期状态
class TaskExpired implements State {
}
@Data
class Task {
    private Long taskId;
    // 初始化为初始态
    private State state = new TaskInit();
    // 更新状态
    public void updateState(ActionType actionType) {
        state.update(this, actionType);
    }
}

// 抽象观察者
interface Observer {
    void response(Long taskId); // 反应
}
// 抽象目标
abstract class Subject {
    protected List<Observer> observers = new ArrayList<Observer>();
    // 增加观察者方法
    public void add(Observer observer) {
        observers.add(observer);
    }
    // 删除观察者方法
    public void remove(Observer observer) {
        observers.remove(observer);
    }
    // 通知观察者方法
    public void notifyObserver(Long taskId) {
        for (Observer observer : observers) {
            observer.response(taskId);
        }
    }
}
// 活动观察者
class ActivityObserver implements Observer {
    private ActivityService activityService;
    @Override
    public void response(Long taskId) {
        activityService.notifyFinished(taskId);
    }
}
// 任务管理观察者
class TaskManageObserver implements Observer {
    private TaskManager taskManager;
    @Override
    public void response(Long taskId) {
        taskManager.release(taskId);
    }
}

// 任务进行状态
class TaskOngoing extends Subject implements State {  
    @Override
    public void update(Task task, ActionType actionType) {
        if (actionType == ActionType.ACHIEVE) {
            task.setState(new TaskFinished());
            // 通知
            notifyObserver(task.getTaskId());
        } else if (actionType == ActionType.STOP) {
            task.setState(new TaskPaused());
        } else if (actionType == ActionType.EXPIRE) {
            task.setState(new TaskExpired());
        }
    }
}
// 任务初始状态
class TaskInit implements State {
    @Override
    public void update(Task task, ActionType actionType) {
        if  (actionType == ActionType.START) {
            TaskOngoing taskOngoing = new TaskOngoing();
            taskOngoing.add(new ActivityObserver());
            taskOngoing.add(new TaskManageObserver());
            task.setState(taskOngoing);
        }
    }
}

// 抽象活动接口
interface ActivityInterface {
    void participate(Long userId);
}
// 活动类
class Activity implements ActivityInterface {
    private String type;
    private Long id;
    private String name;
    private Integer scene;
    private String material;
    public Activity(String type) {
        this.type = type;
        // id的构建部分依赖于活动的type
        if ("period".equals(type)) {
            id = 0L;
        }
    }
    public Activity(String type, Long id) {
        this.type = type;
        this.id = id;
    }
    public Activity(String type, Long id, Integer scene) {
        this.type = type;
        this.id = id;
        this.scene = scene;
    }
    public Activity(String type, String name, Integer scene, String material) {
        this.type = type;
        this.scene = scene;
        this.material = material;
        // name的构建完全依赖于活动的type
        if ("period".equals(type)) {
            this.id = 0L;
            this.name = "period" + name;
        } else {
            this.name = "normal" + name;
        }
    }
    // 参与活动
    @Override
    public void participate(Long userId) {
        // do nothing
    }
}
// 任务型活动
class TaskActivity extends Activity {
    private Task task;
    public TaskActivity(String type, String name, Integer scene, String material, Task task) {
        super(type, name, scene, material);
        this.task = task;
    }
    // 参与任务型活动
    @Override
    public void participate(Long userId) {
        // 更新任务状态为进行中
        task.getState().update(task, ActionType.START);
    }
}

// 活动类
class Activity implements ActivityInterface {
    protected String type;
    protected Long id;
    protected String name;
    protected Integer scene;
    protected String material;
    // 全参构造函数
    public Activity(String type, Long id, String name, Integer scene, String material) {
        this.type = type;
        this.id = id;
        this.name = name;
        this.scene = scene;
        this.material = material;
    }
    @Override
    public void participate(Long userId) {
        // do nothing
    }
    // 静态建造器类，使用奇异递归模板模式允许继承并返回继承建造器类
    public static class Builder<T extends Builder<T>> {
        protected String type;
        protected Long id;
        protected String name;
        protected Integer scene;
        protected String material;
        public T setType(String type) {
            this.type = type;
            return (T) this;
        }
        public T setId(Long id) {
            this.id = id;
            return (T) this;
        }
        public T setId() {
            if ("period".equals(this.type)) {
                this.id = 0L;
            }
            return (T) this;
        }
        public T setScene(Integer scene) {
            this.scene = scene;
            return (T) this;
        }
        public T setMaterial(String material) {
            this.material = material;
            return (T) this;
        }
        public T setName(String name) {
            if ("period".equals(this.type)) {
                this.name = "period" + name;
            } else {
                this.name = "normal" + name;
            }
            return (T) this;
        }
        public Activity build(){
            return new Activity(type, id, name, scene, material);
        }
    }
}
// 任务型活动
class TaskActivity extends Activity {
    protected Task task;
    // 全参构造函数
    public TaskActivity(String type, Long id, String name, Integer scene, String material, Task task) {
        super(type, id, name, scene, material);
        this.task = task;
    }
    // 参与任务型活动
    @Override
    public void participate(Long userId) {
        // 更新任务状态为进行中
        task.getState().update(task, ActionType.START);
    }
    // 继承建造器类
    public static class Builder extends Activity.Builder<Builder> {
        private Task task;
        public Builder setTask(Task task) {
            this.task = task;
            return this;
        }
        public TaskActivity build(){
            return new TaskActivity(type, id, name, scene, material, task);
        }
    }
}

public void participate(Long userId) {
    // 对目标用户做风险控制，失败则抛出异常
    Risk.doControl(userId);
    // 更新任务状态为进行中
    task.state.update(task, ActionType.START);
}

// 抽象装饰角色
abstract class ActivityDecorator implements ActivityInterface {
    protected ActivityInterface activity;
    public ActivityDecorator(ActivityInterface activity) {
        this.activity = activity;
    }
    public abstract void participate(Long userId);
}
// 能够对活动做风险控制的包装类
class RiskControlDecorator extends ActivityDecorator {
    public RiskControlDecorator(ActivityInterface activity) {
        super(activity);
    }
    @Override
    public void participate(Long userId) {
        // 对目标用户做风险控制，失败则抛出异常
        Risk.doControl(userId);
        // 更新任务状态为进行中
        activity.participate(userId);
    }
}