Java 8 重构传统设计模式,是真的优雅!

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:

1. 策略模式

Java 8 重构传统设计模式,是真的优雅!

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。

Java 8 重构传统设计模式,是真的优雅!

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<Object[]> 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<T>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

Java 8 重构传统设计模式,是真的优雅!

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<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<Observer> 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

Java 8 重构传统设计模式,是真的优雅!

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;

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

同样的效果,可以写得很简洁:

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天然就是getNextProcessor的另一种表达。

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