Java 8 重构传统设计模式
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
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：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">public interface OrderService { void saveOrder(String orderNo); }
Mysql策略实现：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">public class MySqlSaveOrderStrategy implements OrderService { @Override public void saveOrder(String orderNo) { System.out.println("order:" + orderNo + " save to mysql"); } }
Nosql策略实现：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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"：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs livescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs cs" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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；
<pre class="prettyprint hljs scala" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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；
<pre class="prettyprint hljs scala" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs gradle" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs cs" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs livescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">public interface Observer { void notify(String orderNo); }
Subject接口:
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">public interface Subject { void registerObserver(Observer o); void notifyAllObserver(String orderNo); }
Subject接口实现：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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:
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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；
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs cpp" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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；
<pre class="prettyprint hljs cpp" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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:
<pre class="prettyprint hljs livescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">public interface Processor { Processor getNextProcessor(); void process(String param); }
抽象实现类：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs scala" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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；
<pre class="prettyprint hljs scala" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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：
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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；
<pre class="prettyprint hljs dart" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">@FunctionalInterface public interface NewProcessor { Consumer<String> process(String param); }
同样的效果，可以写得很简洁：
<pre class="prettyprint hljs rust" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto;">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。
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”。
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