【设计模式】用Java实现代理模式

// 接口：图片
interface Image {
    void display();
}
// 目标对象：真实图片
class RealImage implements Image {
    private String filename;
    public RealImage(String filename) {
        this.filename = filename;
        loadFromDisk();
    }
    private void loadFromDisk() {
        System.out.println("Loading image from disk: " + filename);
    }
    public void display() {
        System.out.println("Displaying image: " + filename);
    }
}
// 代理对象：图片代理
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);
        }
        realImage.display();
    }
}
// 使用示例
public class Main {
    public static void main(String[] args) {
        Image image = new ImageProxy("example.jpg");
        // 第一次显示图像，从磁盘加载
        image.display();
        System.out.println("------------------------------------");
        // 第二次显示图像，直接显示
        image.display();
    }
}

// 接口：商品服务
interface ProductService {
    int getProductStock(String productId);
}
// 目标对象：实际的商品服务
class ProductServiceImpl implements ProductService {
    public int getProductStock(String productId) {
        // 实际的商品库存查询逻辑
        // 假设返回库存为100
        return 100;
    }
}
// 代理对象：商品服务代理
class ProductServiceProxy implements ProductService {
    private ProductService productService;
    public ProductServiceProxy(ProductService productService) {
        this.productService = productService;
    }
    public int getProductStock(String productId) {
        // 在实际对象的方法执行前后添加额外的逻辑
        System.out.println("开始查询商品库存");
        int stock = productService.getProductStock(productId);
        System.out.println("查询商品库存完成");
        return stock;
    }
}
// 使用示例
public class Main {
    public static void main(String[] args) {
        ProductService realProductService = new ProductServiceImpl();
        ProductService productServiceProxy = new ProductServiceProxy(realProductService);
        int stock = productServiceProxy.getProductStock("12345");
        System.out.println("商品库存：" + stock);
    }
}