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
文章目录- 1.策略模式
- 2.模板方法
- 3.观察者模式
- 4.责任链/职责链模式
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。
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
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");
java8重构。可以把上面的3个模板（包括抽象类模板）减少到1个
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
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
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
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】");
}
}
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
static void test1() {
Subject subject = new SubjectImpl();
subject.registerObserver(new OrderObserver());
subject.registerObserver(new StockObserver());
subject.notifyAllObserver("001");
}
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));
}
}
测试
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);
}
}
}
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);
}
}
}
测试
static void test1() {
Processor p1 = new ProcessorImpl1(null);
Processor p2 = new ProcessorImpl2(p1);
p2.process("something happened");
}
java8重构。只需要一个新接口
@FunctionalInterface
public interface NewProcessor {
Consumer process(String param);
}
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
