代理模式

代理设计模式UML类图

代理设计模式java代码实现

/**
 * WizardTower interface.
 精灵塔
 */
public interface WizardTower {

  void enter(Wizard wizard);
}

/**
 * Wizard.
 巫师
 */
public class Wizard {

  private final String name;

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

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

}

/**
 * The object to be proxyed.
 IvoryTower象牙塔
 */
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) {
    if (numWizards < NUM_WIZARDS_ALLOWED) {
      tower.enter(wizard);
      numWizards++;
    } else {
      LOGGER.info("{} is not allowed to enter!", wizard);
    }
  }
}

/**
 * A proxy, in its most general form, is a class functioning as an interface to something else. The
 * proxy could interface to anything: a network connection, a large object in memory, a file, or
 * some other resource that is expensive or impossible to duplicate. In short, a proxy is a wrapper
 * or agent object that is being called by the client to access the real serving object behind the
 * scenes.
 在最一般的形式上，代理是一个类，充当与其他对象的接口。 代理可以与任何接口：网络连接，内存中的大对象，文件或其他昂贵或无法复制的其他资源。 简而言之，代理是客户端调用的包装器或代理对象，以访问幕后的真实服务对象。
 *
 * <p>The Proxy design pattern allows you to provide an interface to other objects by creating a
 * wrapper class as the proxy. The wrapper class, which is the proxy, can add additional
 * functionality to the object of interest without changing the object's code.
 *<p>通过代理设计模式，您可以通过创建包装器类作为代理来为其他对象提供接口。 包装类（它是代理）可以在不更改对象代码的情况下向目标对象添加其他功能。
 * <p>In this example the proxy ({@link WizardTowerProxy}) controls access to the actual object (
 * {@link IvoryTower}).
 <p>在此示例中，代理（{@link WizardTowerProxy}）控制对实际对象（{@link IvoryTower}）的访问。
 */
public class App {

  /**
   * Program entry point.
   */
  public static void main(String[] args) {

    var proxy = new WizardTowerProxy(new IvoryTower());
    proxy.enter(new Wizard("Red wizard"));
    proxy.enter(new Wizard("White wizard"));
    proxy.enter(new Wizard("Black wizard"));
    proxy.enter(new Wizard("Green wizard"));
    proxy.enter(new Wizard("Brown wizard"));

  }
}

应用场景

spring动态代理生成对象

Mybatis中Mapper动态代理机制

dubbo动态代理模式生成proxy过程