代理模式

public interface Image {
   void display();
}

public class RealImage implements Image {

   private String fileName;

   public RealImage(String fileName){
      this.fileName = fileName;
      loadFromDisk(fileName);
   }

   @Override
   public void display() {
      System.out.println("Displaying " + fileName);
   }

   private void loadFromDisk(String fileName){
//第一次新建时执行
      System.out.println("Loading " + fileName);
   }
}

public class ProxyImage implements Image{

   private RealImage realImage;
   private String fileName;

   public ProxyImage(String fileName){
      this.fileName = fileName;
   }

   @Override
   public void display() {
      if(realImage == null){
         realImage = new RealImage(fileName);
      }
      realImage.display();
   }
}

动态代理

    public interface Person {
        void giveMoney();
    }

    public class Student implements Person {
        public Student() {
        }

        @Override
        public void giveMoney() {
            System.out.println ("上交班费50元");
        }
    }

    public class StuInvocationHandler<T> implements InvocationHandler {
        T target;

        public StuInvocationHandler(T target) {
            this.target = target;
        }
        
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            System.out.println("代理执行" +method.getName() + "方法");
            Object result = method.invoke(target, args);
            return result;
        }
    }

        Person zhangsan = new Student();

        //创建一个与代理对象相关联的InvocationHandler
        InvocationHandler stuHandler = new StuInvocationHandler<Person>(zhangsan);
        //创建一个代理对象stuProxy来代理zhangsan，代理对象的每个执行方法都会替换执行Invocation中的invoke方法
        Person stuProxy = (Person) Proxy.newProxyInstance(Person.class.getClassLoader(), new Class<?>[]{Person.class}, stuHandler);
        stuProxy.giveMoney();