中介者模式

中介者
中介者模式：用一个中介对象来封装一系列的对象交互，中介者使各对象不需要显式地相互引用，从而使其耦合松散，而且可以独立地改变它们之间的交互。中介者模式又称为调停者模式，它是一种对象行为型模式。

//创建门派抽象类

package com.md.tertium;

//门派抽象类
public abstract class School {
  protected IPatternAlliance patternAlliance;

  public School(IPatternAlliance patternAlliance) {
      super();
      this.patternAlliance = patternAlliance;
  }
//防御
  public void defense() {
      System.out.println( getName() + "防御" );
  }
  //攻击
  public void attack(School school) {
      System.out.println( getName() + "攻击" + school.getName() );
  }

  //有了中介者，将由中介者处理
  public void attackByPatternAlliance(School school) {
      patternAlliance.resolveAttack( this, school );
  }

  //门派攻击
  public void defenseByPatternAlliance() {
      patternAlliance.attack( this );
  }

  public abstract String getName();
}


package com.md.tertium;

//中介者
public class MediatorSchool extends School {

  public MediatorSchool(IPatternAlliance patternAlliance) {
      super( patternAlliance );
  }

  @Override
  public String getName() {
      return "中介者神阁";
  }
}


package com.md.tertium;

public class CommandSchool extends School {
  public CommandSchool(IPatternAlliance patternAlliance) {
      super( patternAlliance );
  }

  @Override
  public String getName() {
      return "命令门";
  }
}
package com.md.tertium;

public class SingletonSchool extends School {
  public SingletonSchool(IPatternAlliance patternAlliance) {
      super( patternAlliance );
  }

  @Override
  public String getName() {
      return "单例宗";
  }
}
package com.md.tertium;

public class StrategySchool extends School {
  public StrategySchool(IPatternAlliance patternAlliance) {
      super( patternAlliance );
  }

  @Override
  public String getName() {
      return "策略";
  }

}
package com.md.tertium;

import java.util.List;

//模式联盟 中介者接口
public interface IPatternAlliance {
  //提供一个加入联盟的接口
  public abstract void add(School school);

  //防御联盟
  public abstract void resolveAttack(School activeSide, School passiveSide);

  //攻击联盟
  public abstract void attack(School passiveSide);
}
package com.md.tertium;

import java.util.LinkedList;
import java.util.List;

//联盟模式的具体实现
public class PatternAlliance implements IPatternAlliance {

  private List  schoolList = new LinkedList ();

  @Override
  public void add(School school) {
      //加入联盟
      schoolList.add( school );
  }

  @Override
  public void resolveAttack(School activeSide, School passiveSide) {
      if (schoolList.contains( passiveSide )) {
          System.out.println( "被攻方" + passiveSide.getName() + "已加入联盟，联盟将齐力防御！" );
          for (School school : schoolList) {
              school.defense();
          }
      } else {
          System.out.println( "被攻方" + passiveSide.getName() + "未加入联盟，联盟不给予防御帮助！" );
          passiveSide.defense();
      }
  }

  @Override
  public void attack(School passiveSide) {
      if (schoolList.contains( passiveSide ) && schoolList.contains( passiveSide )) {
          System.out.println( "主攻方" + passiveSide.getName() + "以及被攻方" + passiveSide.getName() + "都已加入联盟，不允许内讧！" );
      } else if (schoolList.contains( passiveSide ) && !schoolList.contains( passiveSide )) {
          System.out.println( "主攻方" + passiveSide.getName() + "已加入联盟，被攻方" + passiveSide.getName() + "不在联盟之中，将集体攻打该门派！" );
          for (School school : schoolList) {
              school.attack( passiveSide );
          }
      } else {
          System.out.println( "主攻方" + passiveSide.getName() + "未加入联盟，联盟无权干预此事！" );
          passiveSide.attack( passiveSide );
      }
  }
}
package com.md.tertium;

public class Main {
  public static void main(String[] args) {
//        School singletonSchool = new SingletonSchool();
//        School commandSchool = new CommandSchool();
//        School mediatorSchool = new MediatorSchool();
//
//        singletonSchool.attack( mediatorSchool );
//        commandSchool.attack( mediatorSchool );
//
//        mediatorSchool.defense();
      IPatternAlliance patternAlliance = new PatternAlliance();

      School singletonSchool = new SingletonSchool( patternAlliance );
      School commandSchool = new CommandSchool( patternAlliance );
      School mediatorSchool = new MediatorSchool( patternAlliance );

      School strategySchool = new StrategySchool( patternAlliance );

      //策略宫没有被联盟收留
      patternAlliance.add( mediatorSchool );
      patternAlliance.add( commandSchool );
      patternAlliance.add( singletonSchool );

      singletonSchool.attackByPatternAlliance( mediatorSchool );
      commandSchool.attackByPatternAlliance( mediatorSchool );
      System.out.println( "------------------------------------------------------" );
      mediatorSchool.attackByPatternAlliance( strategySchool );
      System.out.println( "------------------------------------------------------" );
      strategySchool.attackByPatternAlliance( mediatorSchool );
      mediatorSchool.defenseByPatternAlliance();
      System.out.println( "------------------------------------------------------" );
  }
}

《中介者模式》针对的问题是，解决一系列对象之间复杂的耦合关系，这一系列对象往往是“多对多”的耦合关系，《中介者模式》采用一个中介者对象将这一系列对象集中管理，而各个对象也将自己与其它对象的交互行为委托给中介者处理，从而减少这一系列对象之间的耦合。
它的优点倒是非常明显，清除了一系列对象之间复杂的耦合关系，并且中介者可以控制这一系列对象的行为，统一管理。
《中介者模式》的缺点是，由于中介者负责着一系列对象的交互与控制，所以中介者的类会非常复杂，而且一旦中介者类无法正常工作，那么所有将行为委托给中介者的类都将会出现问题，所以在使用的时候还是要特别小心。