定义:
用一个中介对象封装一系列的对象交互,中介者使各对象不需要显示地相互作用,从而使其耦合松散,而且可以独立的改变它们之间的交互。
举例(采购-销售-库房例子):
问题所在:如果销售一批产品,那么库房要改变,采购可能也要改变,这是每个类都会与其它类有依赖,耦合十分严重,此时就引出了中介者模式。下面看下类图:
public abstract class AbstractMediator { protected Purchase purchase; protected Sale sale; protected Stock stock; //构造函数 public AbstractMediator(){ purchase = new Purchase(this); sale = new Sale(this); stock = new Stock(this); } //中介者最重要的方法,叫做事件方法,处理多个对象之间的关系 public abstract void execute(String str,Object...objects); } ------------------------------------------------------------------------ public class Mediator extends AbstractMediator { //中介者最重要的方法 public void execute(String str,Object...objects){ if(str.equals("purchase.buy")){ //采购电脑 this.buyComputer((Integer)objects[0]); }else if(str.equals("sale.sell")){ //销售电脑 this.sellComputer((Integer)objects[0]); }else if(str.equals("sale.offsell")){ //折价销售 this.offSell(); }else if(str.equals("stock.clear")){ //清仓处理 this.clearStock(); } } //采购电脑 private void buyComputer(int number){ int saleStatus = super.sale.getSaleStatus(); if(saleStatus>80){ //销售情况良好 System.out.println("采购IBM电脑:"+number + "台"); super.stock.increase(number); }else{ //销售情况不好 int buyNumber = number/2; //折半采购 System.out.println("采购IBM电脑:"+buyNumber+ "台"); } } //销售电脑 private void sellComputer(int number){ if(super.stock.getStockNumber()<number){ //库存数量不够销售 super.purchase.buyIBMcomputer(number); } super.stock.decrease(number); } //折价销售电脑 private void offSell(){ System.out.println("折价销售IBM电脑"+stock.getStockNumber()+"台"); } //清仓处理 private void clearStock(){ //要求清仓销售 super.sale.offSale(); //要求采购人员不要采购 super.purchase.refuseBuyIBM(); } } ------------------------------------------------------------------ public abstract class AbstractColleague { protected AbstractMediator mediator; public AbstractColleague(AbstractMediator _mediator){ this.mediator = _mediator; } } public class Purchase extends AbstractColleague{ public Purchase(AbstractMediator _mediator){ super(_mediator); } //采购IBM型号的电脑 public void buyIBMcomputer(int number){ super.mediator.execute("purchase.buy", number); } //不在采购IBM电脑 public void refuseBuyIBM(){ System.out.println("不再采购IBM电脑"); } } ----------------------------------------------------------------- public class Stock extends AbstractColleague { public Stock(AbstractMediator _mediator){ super(_mediator); } //刚开始有100台电脑 private static int COMPUTER_NUMBER =100; //库存增加 public void increase(int number){ COMPUTER_NUMBER = COMPUTER_NUMBER + number; System.out.println("库存数量为:"+COMPUTER_NUMBER); } //库存降低 public void decrease(int number){ COMPUTER_NUMBER = COMPUTER_NUMBER - number; System.out.println("库存数量为:"+COMPUTER_NUMBER); } //获得库存数量 public int getStockNumber(){ return COMPUTER_NUMBER; } //存货压力大了,就要通知采购人员不要采购,销售人员要尽快销售 public void clearStock(){ System.out.println("清理存货数量为:"+COMPUTER_NUMBER); super.mediator.execute("stock.clear"); } } -------------------------------------------------------------------- public class Sale extends AbstractColleague { public Sale(AbstractMediator _mediator){ super(_mediator); } //销售IBM型号的电脑 public void sellIBMComputer(int number){ super.mediator.execute("sale.sell", number); System.out.println("销售IBM电脑"+number+"台"); } //反馈销售情况,0——100之间变化,0代表根本就没人卖,100代表非常畅销,出1一个卖一个 public int getSaleStatus(){ Random rand = new Random(System.currentTimeMillis()); int saleStatus = rand.nextInt(100); System.out.println("IBM电脑的销售情况为:"+saleStatus); return saleStatus; } //折价处理 public void offSale(){ super.mediator.execute("sale.offsell"); } } ------------------------------------------------------------------- public class Client { public static void main(String[] args) { AbstractMediator mediator = new Mediator(); //采购人员采购电脑 System.out.println("------采购人员采购电脑--------"); Purchase purchase = new Purchase(mediator); purchase.buyIBMcomputer(100); //销售人员销售电脑 System.out.println("\n------销售人员销售电脑--------"); Sale sale = new Sale(mediator); sale.sellIBMComputer(1); //库房管理人员管理库存 System.out.println("\n------库房管理人员清库处理--------") Stock stock = new Stock(mediator); stock.clearStock(); } }
总结:
使用中介者模式的情况:
1、 N 个对象之间产生了相互的依赖关系,其中 N 大于 2,注意是相互的依赖;
2、多个对象有依赖关系,但是依赖的行为尚不确定或者有发生改变的可能,在这种情况下一般建议采 用中介者模式,降低变更引起的风险扩散;
3、产品开发。其中一个明显的例子就是 MVC 框架,把这个应用到产品中,可以提升产品的性能和扩展性,但是作为项目开发就未必,项目是以交付投产为目标,而产品以稳定、高效、扩展为宗旨。