代理模式类型：
- 远程代理：控制对远程对象的访问
- 虚拟代理：延迟创建昂贵对象
- 保护代理：控制访问权限
- 缓存代理：缓存请求结果
- 智能引用代理：在访问对象时执行额外操作

// 主题接口
public interface Image {
    void display();
}

// 真实主题
public class RealImage implements Image {
    private String filename;
    
    public RealImage(String filename) {
        this.filename = filename;
        loadImageFromFile();  // 昂贵的操作
    }
    
    private void loadImageFromFile() {
        System.out.println("Loading image: " + filename);
    }
    
    public void display() {
        System.out.println("Displaying: " + filename);
    }
}

// 代理
public class ImageProxy implements Image {
    private String filename;
    private RealImage realImage;
    
    public ImageProxy(String filename) {
        this.filename = filename;
    }
    
    public void display() {
        if (realImage == null) {
            realImage = new RealImage(filename);  // 延迟创建
        }
        realImage.display();
    }
}

// Java 动态代理
public interface Subject {
    void request();
}

public class RealSubject implements Subject {
    public void request() { System.out.println("RealSubject"); }
}

public class ProxyInvocationHandler implements InvocationHandler {
    private Object target;
    
    public ProxyInvocationHandler(Object target) {
        this.target = target;
    }
    
    public Object invoke(Object proxy, Method method, Object[] args) {
        System.out.println("Before");
        Object result = method.invoke(target, args);
        System.out.println("After");
        return result;
    }
}

// 使用
Subject proxy = (Subject) Proxy.newProxyInstance(
    RealSubject.class.getClassLoader(),
    new Class[]{Subject.class},
    new ProxyInvocationHandler(new RealSubject())
);
proxy.request();

public class CachedService implements Service {
    private Service realService;
    private Map<String, Object> cache = new HashMap<>();
    
    public Object request(String key) {
        if (!cache.containsKey(key)) {
            cache.put(key, realService.request(key));
        }
        return cache.get(key);
    }
}