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前沿热点:Java 8 重构传统设计模式,是真的优雅!

2022-08-19 09:54:42来源:码猿技术专栏

java8中提供的很多新特性可以用来重构传统设计模式中的写法,下面是一些示例:


【资料图】

1. 策略模式

上图是策略模式的类图,假设我们现在要保存订单,OrderService接口定义要做什么,而NoSqlSaveOrderStragegy以及MySqlSaveOrderStrategy则提供了二种策略,分别是保存到nosql数据库,以及传统的mysql关系型数据库,最后在OrderServiceExecutor中通过构造函数注入最终要使用的策略。

传统写法,这个场景至少得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");    }}

使用策略的辅助"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,可以省去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. 模板方法

类图如下,核心思路是把一些通用的标准方法,在抽象父类里仅定义方法签名,实现逻辑交给子类。

比如:会员系统中,每个商家都会有一些营销活动,需要推送某种信息给会员,但是不同的商家推送的内容可能不同,有些需要推送优惠券,有些需要积分通知。

抽象模板类:

public abstract class AbstractPushTemplate {    public void push(int customerId, String shopName) {        System.out.println("准备推送...");        execute(customerId, shopName);        System.out.println("推送完成\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");    }}

使用示例:

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方式越多,子类就越多。

使用java8重构后,可以把上面的3个模板(包括抽象类模板)减少到1个,参考下面:

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

借助Consumer这个function interface,可以省去实现子类,具体的实现留到使用时再来决定,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,然后一堆观察者Observer注册到主题上,有事件发生时,subject根据注册列表,去通知所有的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 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【已支付】");    }}

StockObserver;

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

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,接口可以提供默认实现方法,我们弄一个新的主题接口;

public interface NewSubject {    List list = new ArrayList<>();    default void registerObserver(Observer o) {        list.add(o);    }    default void nofityAllObserver(String orderNo) {        list.forEach(c -> c.notify(orderNo));    }}

使用:

static void test2() {    NewSubject subject = new NewSubject() {    };    subject.registerObserver((String orderNo) -> System.out.println("订单 " + orderNo + " 状态更新为【已支付】"));    subject.registerObserver((String orderNo) -> System.out.println("订单 " + orderNo + " 已通知库房发货!"));    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:每个处理环节,都有一个“指针”指向下一个处理者,类似链表一样。

Processor接口:

public interface Processor {    Processor getNextProcessor();    void process(String param);}

抽象实现类:

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);        }    }}

使用示例:

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

用java8重构后,只需要一个新接口;

@FunctionalInterfacepublic interface NewProcessor {    Consumer process(String param);}

同样的效果,可以写得很简洁:

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

andThen天然就是getNextProcessor的另一种表达。

重要提示:什么时候该用lambda,什么时候不用,这是要看情况的,如果处理逻辑相对比较简单,可以用lamdba来重构,以便让代码更简洁易读,如果处理逻辑很复杂,应该还是用“类”。

关键词: 观察者模式 设计模式 什么时候 运行测试 可以用来

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