委派模式
委派模式，可以精简程序逻辑，提升代码的可读性。
委派模式（Delegate Pattern）的基本作用就是负责任务的调用和分配任务。
例如：老板（Boss）给项目经理（Leader）下达任务，项目经理会根据实际情况给每个员工派发工作任务，待员工把工作任务完成之后，再由项目经理汇报工作进度和结果给老板。
和代理模式的区别
跟代理模式很像，可以看做是一种特殊情况下的静态代理的全权代理，但是代理模式注重过程，而委派模式注重结果。委派模式在Spring 中应用非常多，常用的DispatcherServlet 其实就是用到了委派模式。
案例
public interface IEmployee { void doing(String command); }
public class EmployeeA implements IEmployee { @Override public void doing(String command) { System.out.println("我是员工A，我现在开始干" + command + "工作"); } } ```java public class EmployeeB implements IEmployee { @Override public void doing(String command) { System.out.println("我是员工B，我现在开始干" + command + "工作"); } }
public class Leader implements IEmployee { private Map<String, IEmployee> targets = new HashMap<>(); public Leader() { targets.put("登录", new EmployeeA()); targets.put("加密", new EmployeeB()); } @Override public void doing(String command) { targets.get(command).doing(command); } }
public class Boss { public void command(String command, Leader leader) { leader.doing(command); } }
测试:
public class DelegateTest { public static void main(String[] args) { //客户请求（Boss）、委派者（Leader）、被被委派者（Target） //委派者要持有被委派者的引用 //代理模式注重的是过程， 委派模式注重的是结果 //策略模式注重是可扩展（外部扩展），委派模式注重内部的灵活和复用 //委派的核心：就是分发、调度、派遣 //委派模式：就是静态代理和策略模式一种特殊的组合 new Boss().command("登录",new Leader()); new Boss().command("加密", new Leader()); } }
应用场景
手写一个DispatcherServlet: DispatcherServlet根据url分配到对应的controller的method方法就体现了委派模式。
public class DispatcherServlet extends HttpServlet { @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { doDispatch(req, resp); } catch (Exception e) { e.printStackTrace(); } } private void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { String uri = request.getRequestURI(); String mid = request.getParameter("mid"); if ("/getMemberById".equals(uri)) { new MemberController().getMemberById(mid); } else if ("/getOrderById".equals(uri)) { new OrderController().getOrderById(mid); } else if ("/logout".equals(uri)) { new SystemController().logout(); } else { response.getWriter().write("404 Not Found!!"); } }
public class MemberController { public void getMemberById(String mid){ System.out.println(mid); } }
public class OrderController { public void getOrderById(String mid){ } }
public class SystemController { public void logout(){ } }
策略模式
介绍
策略模式（Strategy Pattern）是指定义了算法家族、分别封装起来，让它们之间可以互相替换，此模式让算法的变化不会影响到使用算法的用户。
策略模式的应用场景
1、假如系统中有很多类，而他们的区别仅仅在于他们的行为不同。
2、一个系统需要动态地在几种算法中选择一种。
案例1。
课程经常会有优惠活动，优惠策略会有很多种可能
如：领取优惠券抵扣、返现促销、拼团优惠。下面我们用代码来模拟，首先我们创建一
个促销策略的抽象PromotionStrategy
public interface PromotionStrategy { void doPromotion(); }
/** * 返现活动 * Created by HFL */ public class CashbackStrategy implements PromotionStrategy { @Override public void doPromotion() { System.out.println("返现促销,返回的金额转到支付宝账号"); } }
/** * 优惠券 * */ public class CouponStrategy implements PromotionStrategy { @Override public void doPromotion() { System.out.println("领取优惠券,课程的价格直接减优惠券面值抵扣"); } }
/** * 无优惠 * */ public class EmptyStrategy implements PromotionStrategy { @Override public void doPromotion() { System.out.println("无促销活动"); } }
/** * 拼团优惠 * */ public class GroupbuyStrategy implements PromotionStrategy{ @Override public void doPromotion() { System.out.println("拼团，满20人成团，全团享受团购价"); } }
优惠活动
public class PromotionActivity { private PromotionStrategy promotionStrategy; public PromotionActivity(PromotionStrategy promotionStrategy) { this.promotionStrategy = promotionStrategy; } public void execute(){ promotionStrategy.doPromotion(); } }
测试1：
public class PromotionActivityTest { public static void main(String[] args) { PromotionActivity activity618 = new PromotionActivity(new CouponStrategy()); PromotionActivity activity1111 = new PromotionActivity(new CashbackStrategy()); activity618.execute(); activity1111.execute(); }
根据前端的条件选择哪种策略方式:
public static void main(String[] args) { PromotionActivity promotionActivity = null; String promotionKey = "CASHBACK"; if(StringUtils.equals(promotionKey,"COUPON")){ promotionActivity = new PromotionActivity(new CouponStrategy()); }else if(StringUtils.equals(promotionKey,"CASHBACK")){ promotionActivity = new PromotionActivity(new CashbackStrategy()); }//...... promotionActivity.execute(); }
从形式上看，这这个测试类根据条件，类似简单工厂。所以我们可以改成简单工厂的方法优化下:
再写个简单工厂类.用于生产策略类:
public class PromotionStrategyFactory { private static Map<String,PromotionStrategy> PROMOTION_STRATEGY_MAP = new HashMap<String, PromotionStrategy>(); static { PROMOTION_STRATEGY_MAP.put(PromotionKey.COUPON,new CouponStrategy()); PROMOTION_STRATEGY_MAP.put(PromotionKey.CASHBACK,new CashbackStrategy()); PROMOTION_STRATEGY_MAP.put(PromotionKey.GROUPBUY,new GroupbuyStrategy()); } private static final PromotionStrategy NON_PROMOTION = new EmptyStrategy(); private PromotionStrategyFactory(){} public static PromotionStrategy getPromotionStrategy(String promotionKey){ PromotionStrategy promotionStrategy = PROMOTION_STRATEGY_MAP.get(promotionKey); return promotionStrategy == null ? NON_PROMOTION : promotionStrategy; } private interface PromotionKey{ String COUPON = "COUPON"; String CASHBACK = "CASHBACK"; String GROUPBUY = "GROUPBUY"; } }
重写测试类:
public static void main(String[] args) { String promotionKey = "GROUPBUY"; PromotionActivity promotionActivity = new PromotionActivity(PromotionStrategyFactory.getPromotionStrategy(promotionKey)); promotionActivity.execute(); }
