策略模式实现方式之Map<K,Function>

小概念

场景

• 我们有一个对象
• 对象有一个行为
• 该行为在不同场景中有不同的表现形式

策略模式

• 定义了一系列算法
• 封装了每个算法
• 这一系列的算法可互换代替

代码实现

定义一个对象行为表现形式枚举

    //定义一个对象行为表现形式枚举
    public enum AdApplyTypeEnum implements BaseEnum<Integer> {

    /**
     * 价值鉴定
     */
    WORTH(1, "价值鉴定","JZJD",3);

    Integer value;

    /**
     * 名称
     */
    String name;

    /**
     * 申请单编号编码前缀
     */
    String code;

    /**
     * 鉴定类型对应工作流模板类型
     */
    Integer wfType;

    AdApplyTypeEnum(Integer value, String name, String code,Integer wfType) {
        this.value = value;
        this.name = name;
        this.code = code;
        this.wfType = wfType;
    }

    /**
     * 获取枚举值
     *
     * @return value
     */
    @Override
    public Integer getValue() {
        return value;
    }

    /**
     * 根据枚举值获取枚举类型
     *
     * @param value 枚举值
     * @return FormStateEnum
     */
    public static AdApplyTypeEnum valueOf(Integer value) {
        for (AdApplyTypeEnum typeEnum : AdApplyTypeEnum.values()) {
            if (typeEnum.getValue().equals(value)) {
                return typeEnum;
            }
        }
        return AdApplyTypeEnum.OTHER;
    }
}

定义每种表现形式

/**
 *价值
 **/
private boolean updateWorth(AdApplyDataPO adApplyDataPO) {

}
/**
 * 销毁
 **/
private boolean updateDestroy(AdApplyDataPO adApplyDataPO) {
        
}

封装Map<K,Funtion> 和 初始化算法的对应的函数

    /**
     * 鉴定完成业务逻辑
     */
    private final Map<AdApplyTypeEnum, Function<AdApplyDataPO, Boolean>> applyTypeBusinessLogicMap = new HashMap<>(16);

    /**
     * 初始化鉴定类型对应鉴定完成后业务逻辑
     */
    @PostConstruct
    private void initApplyTypeBusinessLogicMap() {
        applyTypeBusinessLogicMap.put(AdApplyTypeEnum.WORTH, this::updateWorth);
        applyTypeBusinessLogicMap.put(AdApplyTypeEnum.DESTROY, this::updateDestroy);
        applyTypeBusinessLogicMap.put(AdApplyTypeEnum.DECRYPT, this::updateDecrypt);
        applyTypeBusinessLogicMap.put(AdApplyTypeEnum.OPEN, this::updateOpen);
    }

具体应用

    //参数
    AdApplyDataPO adApplyDataPO;
    //K值
    AdApplyTypeEnum adApplyType;
    //调用
    applyTypeBusinessLogicMap.get(adApplyType).apply(adApplyDataPO);

其他实现方式

利用java的多态特性

• 使用接口的多实现
• 子类继承父类重写父类的方法

代码实现

//StrategyExample test application

class StrategyExample {

    public static void main(String[] args) {

        Context context;

        // Three contexts following different strategies
        context = new Context(new FirstStrategy());
        context.execute();

        context = new Context(new SecondStrategy());
        context.execute();

        context = new Context(new ThirdStrategy());
        context.execute();

    }

}

// The classes that implement a concrete strategy should implement this

// The context class uses this to call the concrete strategy
interface Strategy {

    void execute();
    
}

// Implements the algorithm using the strategy interface
class FirstStrategy implements Strategy {

    public void execute() {
        System.out.println("Called FirstStrategy.execute()");
    }
    
}

class SecondStrategy implements Strategy {

    public void execute() {
        System.out.println("Called SecondStrategy.execute()");
    }
    
}

class ThirdStrategy implements Strategy {

    public void execute() {
        System.out.println("Called ThirdStrategy.execute()");
    }
    
}

// Configured with a ConcreteStrategy object and maintains a reference to a Strategy object
class Context {

    Strategy strategy;

    // Constructor
    public Context(Strategy strategy) {
        this.strategy = strategy;
    }

    public void execute() {
        this.strategy.execute();
    }

}

还有一种在枚举中实现

但是这种我很少见到别人使用，不知道是不符合规范还是什么原因
不知道还有没有其他更好用的方式了

实现示例

enum PaymentStrategy {
    CREDIT_CARD {
        @Override
        void pay(int amount) {
            System.out.println("Paid " + amount + " dollars by credit card");
        }
    },
    PAYPAL {
        @Override
        void pay(int amount) {
            System.out.println("Paid " + amount + " dollars by PayPal");
        }
    };

    abstract void pay(int amount);
}

public class ShoppingCart {
    private PaymentStrategy paymentStrategy;

    public void setPaymentStrategy(PaymentStrategy paymentStrategy) {
        this.paymentStrategy = paymentStrategy;
    }

    public void checkout(int amount) {
        paymentStrategy.pay(amount);
    }

    public static void main(String[] args) {
        ShoppingCart cart = new ShoppingCart();
        cart.setPaymentStrategy(PaymentStrategy.CREDIT_CARD);
        cart.checkout(100);

        cart.setPaymentStrategy(PaymentStrategy.PAYPAL);
        cart.checkout(50);
    }
}