关于前端:Java-8-重构传统设计模式是真的优雅

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java8 中提供的很多新个性能够用来重构传统设计模式中的写法,上面是一些示例:

1. 策略模式

上图是策略模式的类图,假如咱们当初要保留订单,OrderService 接口定义要做什么,而 NoSqlSaveOrderStragegy 以及 MySqlSaveOrderStrategy 则提供了二种策略,别离是保留到 nosql 数据库,以及传统的 mysql 关系型数据库,最初在 OrderServiceExecutor 中通过构造函数注入最终要应用的策略。

传统写法,这个场景至多得 4 个类,代码如下:

OrderService 接口:

public interface OrderService {void saveOrder(String orderNo);
}

Mysql 策略实现:

public class MySqlSaveOrderStrategy implements OrderService {
    @Override
    public void saveOrder(String orderNo) {System.out.println("order:" + orderNo + "save to mysql");
    }
}

Nosql 策略实现:

public class NoSqlSaveOrderStrategy implements OrderService {
    @Override
    public void saveOrder(String orderNo) {System.out.println("order:" + orderNo + "save to nosql");
    }
}

应用策略的辅助 ” 容器 ”:

public class OrderServiceExecutor {

    private final OrderService service;

    public OrderServiceExecutor(OrderService service) {this.service = service;}

    public void save(String orderNo) {this.service.saveOrder(orderNo);
    }

}

运行测试类:

public class OrderServiceTest {public static void main(String[] args) {OrderServiceExecutor executor1 = new OrderServiceExecutor(new MySqlSaveOrderStrategy());
        executor1.save("001");
        OrderServiceExecutor executor2 = new OrderServiceExecutor(new NoSqlSaveOrderStrategy());
        executor2.save("002");
    }
}

重构后,能够省去 2 个策略实现类,代码如下:

public static void main(String[] args) {OrderServiceExecutor executor1 = new OrderServiceExecutor((String orderNo) -> System.out.println("order:" + orderNo + "save to mysql"));
    executor1.save("001");

    OrderServiceExecutor executor2 = new OrderServiceExecutor((String orderNo) -> System.out.println("order:" + orderNo + "save to nosql"));
    executor2.save("002");
}

2. 模板办法

类图如下,外围思路是把一些通用的规范办法,在形象父类里仅定义方法签名,实现逻辑交给子类。

比方:会员零碎中,每个商家都会有一些营销流动,须要推送某种信息给会员,然而不同的商家推送的内容可能不同,有些须要推送优惠券,有些须要积分告诉。

形象模板类:

public abstract class AbstractPushTemplate {public void push(int customerId, String shopName) {System.out.println("筹备推送...");
        execute(customerId, shopName);
        System.out.println("推送实现 \n");
    }

    abstract protected void execute(int customerId, String shopName);
}

优惠券的具体模板;

public class PushCouponTemplate extends AbstractPushTemplate {

    @Override
    protected void execute(int customerId, String shopName) {System.out.println("会员:" + customerId + ", 你好," + shopName + "送您一张优惠券");
    }
}

积分的具体模板;

public class PushScoreTemplate extends AbstractPushTemplate {

    @Override
    protected void execute(int customerId, String shopName) {System.out.println("会员:" + customerId + ", 你好," + shopName + "送您 10 个积分");
    }
}

应用示例:

AbstractPushTemplate template1 = new PushCouponTemplate();
template1.push(1, "糖果店");

AbstractPushTemplate template2 = new PushScoreTemplate();
template2.push(1, "服装店");

显然如果模板的实现形式越多,子类就越多。

应用 java8 重构后,能够把下面的 3 个模板(包含抽象类模板)缩小到 1 个,参考上面:

public class PushTemplateLambda {public void push(int customerId, String shopName, Consumer<Object[]> execute) {System.out.println("筹备推送...");
        Object[] param = new Object[]{customerId, shopName};
        execute.accept(param);
        System.out.println("推送实现 \n");
    }
}

借助 Consumer<T> 这个 function interface,能够省去实现子类,具体的实现留到应用时再来决定,如:

new PushTemplateLambda().push(1, "糖果店", (Object[] obj) -> {System.out.println("会员:" + obj[0] + ", 你好," + obj[1] + "送您一张优惠券");
});

new PushTemplateLambda().push(1, "服装店", (Object[] obj) -> {System.out.println("会员:" + obj[0] + ", 你好," + obj[1] + "送您 10 个积分");
});

3. 观察者模式

思路:基于某个 Subject 主题,而后一堆观察者 Observer 注册到主题上,有事件产生时,subject 依据注册列表,去告诉所有的 observer。

Observer 接口:

public interface Observer {void notify(String orderNo);
}

Subject 接口:

public interface Subject {void registerObserver(Observer o);
    void notifyAllObserver(String orderNo);
}

Subject 接口实现:

public class SubjectImpl implements Subject {private final List<Observer> list = new ArrayList<>();
    @Override
    public void registerObserver(Observer o) {list.add(o);
    }
    @Override
    public void notifyAllObserver(String orderNo) {list.forEach(c -> c.notify(orderNo));
    }
}

观察者的二个实现:

OrderObserver:

public class OrderObserver implements Observer {
    @Override
    public void notify(String orderNo) {System.out.println("订单" + orderNo + "状态更新为【已领取】");
    }
}

StockObserver;

public class StockObserver implements Observer {
    @Override
    public void notify(String orderNo) {System.out.println("订单" + orderNo + "已告诉库房发货!");
    }
}

测试一把:

static void test1() {Subject subject = new SubjectImpl();
    subject.registerObserver(new OrderObserver());
    subject.registerObserver(new StockObserver());
    subject.notifyAllObserver("001");
}

用 java8 重构后,接口能够提供默认实现办法,咱们弄一个新的主题接口;

public interface NewSubject {List<Observer> list = new ArrayList<>();

    default void registerObserver(Observer o) {list.add(o);
    }

    default void nofityAllObserver(String orderNo) {list.forEach(c -> c.notify(orderNo));
    }
}

应用:

static void test2() {NewSubject subject = new NewSubject() { };
    subject.registerObserver((String orderNo) -> System.out.println("订单" + orderNo + "状态更新为【已领取】"));
    subject.registerObserver((String orderNo) -> System.out.println("订单" + orderNo + "已告诉库房发货!"));
    subject.nofityAllObserver("002");
}

只用 2 个接口实现了观察者模式。

4. 责任链 / 职责链模式

核心思想:每个解决环节,都有一个“指针”指向下一个解决者,相似链表一样。

Processor 接口:

public interface Processor {Processor getNextProcessor();

    void process(String param);
}

形象实现类:

public abstract class AbstractProcessor implements Processor {

    private Processor next;

    public AbstractProcessor(Processor processor) {this.next = processor;}

    @Override
    public Processor getNextProcessor() {return next;}

    @Override
    public abstract void process(String param);
}

定义 2 个具体的实现:

public class ProcessorImpl1 extends AbstractProcessor {public ProcessorImpl1(Processor processor) {super(processor);
    }

    @Override
    public void process(String param) {System.out.println("processor 1 is processing:" + param);
        if (getNextProcessor() != null) {getNextProcessor().process(param);
        }
    }
}

及;

public class ProcessorImpl2 extends AbstractProcessor {public ProcessorImpl2(Processor next) {super(next);
    }

    @Override
    public void process(String param) {System.out.println("processor 2 is processing:" + param);
        if (getNextProcessor() != null) {getNextProcessor().process(param);
        }
    }
}

应用示例:

static void test1() {Processor p1 = new ProcessorImpl1(null);
    Processor p2 = new ProcessorImpl2(p1);
    p2.process("something happened");
}

用 java8 重构后,只须要一个新接口;

@FunctionalInterface
public interface NewProcessor {Consumer<String> process(String param);
}

同样的成果,能够写得很简洁:

static void test2() {Consumer<String> p1 = param -> System.out.println("processor 1 is processing:" + param);
    Consumer<String> p2 = param -> System.out.println("processor 2 is processing:" + param);
    p2.andThen(p1).accept("something happened");
}

andThen 人造就是 getNextProcessor 的另一种表白。

重要提醒:什么时候该用 lambda,什么时候不必,这是要看状况的,如果解决逻辑绝对比较简单,能够用 lamdba 来重构,以便让代码更简洁易读,如果解决逻辑很简单,应该还是用“类”。

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