什么是代理？什么是代理类？

代理类相当于古代的摄政王！

//接口
public interface Subject {
  void request();
}

// 被代理的类
public class RealSubject implements Subject{

  @Override
  public void request() {
    System.out.println("RealSubject request"); 
  }
}

// 代理类
public class Proxy implements Subject{

  private RealSubject realSubject;

  public Proxy(RealSubject realSubject) {
    this.realSubject = realSubject;
  }

  @Override
  public void request() {
    // 预处理
    preRequest();
    
    // 调用真实主题
    realSubject.request();

    // 后处理
    postRequest();
  }

  private void preRequest() {
    System.out.println("Proxy preRequest");
  }

  private void postRequest() {
    System.out.println("Proxy postRequest");
  }

}