设计模式-代理模式

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代理模式 (Proxy)

参考: https://github.com/iluwatar/java-design-patterns

故事描述

巫师需要进入象牙塔才能保卫家园,象牙塔只能容纳3位巫师,这里使用代理模式来控制巫师进入象牙塔

个人理解

代理,客户端访问的是真实对象的包装或代理对象,由代理对象简单的访问真实对象,或者添加额外的逻辑. Spring 的事务控制使用的就是代理模式.

Java 代码

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/**
 * 
 * Wizard
 *
 */
public class Wizard {

  private final String name;

  public Wizard(String name) {
    this.name = name;
  }

  @Override
  public String toString() {
    return name;
  }

}

/**
 * WizardTower interface
 */
public interface WizardTower {

  void enter(Wizard wizard);
}

/**
 * 
 * 需要代理的对象
 * 
 */
public class IvoryTower implements WizardTower {

  private static final Logger LOGGER = LoggerFactory.getLogger(IvoryTower.class);

  public void enter(Wizard wizard) {
    LOGGER.info("{} enters the tower.", wizard);
  }

}


/**
 * 
 * The proxy controlling access to the {@link IvoryTower}.
 * 
 */
public class WizardTowerProxy implements WizardTower {

  private static final Logger LOGGER = LoggerFactory.getLogger(WizardTowerProxy.class);

  private static final int NUM_WIZARDS_ALLOWED = 3;

  private int numWizards;

  private final WizardTower tower;

  public WizardTowerProxy(WizardTower tower) {
    this.tower = tower;
  }

  @Override
  public void enter(Wizard wizard) {
    // 控制进入塔内巫师的数量
    if (numWizards < NUM_WIZARDS_ALLOWED) {
      tower.enter(wizard);
      numWizards++;
    } else {
      LOGGER.info("{} is not allowed to enter!", wizard);
    }
  }
}