使用Java Stream高效过滤嵌套列表数据并提取特定信息

 product A :{
    name: a
    images: [
      {
           img1: 1
           url: url1
           type: [
             {
               format: jpg
             }
             {
               format: png
             }
          ]
      },
      {
           img2: 1
           url: url2
           type: [
             {
               format: mp4
             }
             {
               format: png
             }
          ]
      },
      {
           img3: 3
           url: url3
           type: [
             {
               format: jpg
             }
             {
               format: mp4
             }
          ]
      }
    ]
}

import java.net.URL;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
import java.util.function.BinaryOperator;
import java.util.function.Predicate;
import java.util.Arrays;
import java.util.Collection;

// 产品类（在此示例中简化，只关注图片列表）
class Product {
    private String name;
    private List<Image> images;

    public Product(String name, List<Image> images) {
        this.name = name;
        this.images = images;
    }

    public String getName() {
        return name;
    }

    public List<Image> getImages() {
        return images;
    }
}

// 图片类
class Image {
    private String id; // img1, img2, etc.
    private URL url;
    private List<ImageType> types;

    public Image(String id, String url, List<ImageType> types) {
        this.id = id;
        try {
            this.url = new URL(url);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        this.types = types;
    }

    public String getId() {
        return id;
    }

    public URL getUrl() {
        return url;
    }

    public List<ImageType> getTypes() {
        return types;
    }
}

// 图片类型类
class ImageType {
    public enum Format {
        JPG, PNG, MP4, GIF; // 定义支持的格式
    }

    private Format format;

    public ImageType(Format format) {
        this.format = format;
    }

    public Format getFormat() {
        return format;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ImageType imageType = (ImageType) o;
        return format == imageType.format;
    }

    @Override
    public int hashCode() {
        return Objects.hash(format);
    }
}

public class ImageProcessor {

    // 定义一个BinaryOperator，用于将字符串用逗号连接
    static final BinaryOperator<String> reducer = (a, b) -> a + "," + b;

    // 定义一个Predicate，用于判断图片是否包含JPG格式
    static final Predicate<Image> isJpg = (image) -> image.getTypes().stream()
                                                            .anyMatch(type -> type.getFormat() == ImageType.Format.JPG);

    /**
     * 从图片集合中获取所有包含JPG格式的图片URL，并以逗号分隔。
     *
     * @param images 图片集合
     * @return 逗号分隔的JPG图片URL字符串，如果没有匹配项则返回"No Match!"
     */
    public static String getJpgUrls(final Collection<Image> images) {
        return images.stream()
                     .filter(isJpg) // 步骤1: 过滤出包含JPG格式的图片
                     .map(Image::getUrl) // 步骤2: 将Image对象映射为URL对象
                     .map(URL::toString) // 步骤2: 将URL对象映射为URL字符串
                     .reduce(reducer) // 步骤3: 将所有URL字符串用逗号连接
                     .orElse("No Match!"); // 如果没有匹配项，则返回默认值
    }

    public static void main(String[] args) {
        // 构造示例数据
        List<Image> productAImages = Arrays.asList(
            new Image("img1", "http://example.com/url1.jpg", Arrays.asList(new ImageType(ImageType.Format.JPG), new ImageType(ImageType.Format.PNG))),
            new Image("img2", "http://example.com/url2.mp4", Arrays.asList(new ImageType(ImageType.Format.MP4), new ImageType(ImageType.Format.PNG))),
            new Image("img3", "http://example.com/url3.jpg", Arrays.asList(new ImageType(ImageType.Format.JPG), new ImageType(ImageType.Format.MP4))),
            new Image("img4", "http://example.com/url4.gif", Arrays.asList(new ImageType(ImageType.Format.GIF)))
        );

        Product productA = new Product("Product A", productAImages);

        // 调用方法获取JPG图片URL
        String jpgUrls = getJpgUrls(productA.getImages());
        System.out.println("JPG URLs for Product A: " + jpgUrls); // 预期输出: http://example.com/url1.jpg,http://example.com/url3.jpg

        // 测试没有匹配项的情况
        List<Image> noJpgImages = Arrays.asList(
            new Image("img5", "http://example.com/url5.png", Arrays.asList(new ImageType(ImageType.Format.PNG))),
            new Image("img6", "http://example.com/url6.mp4", Arrays.asList(new ImageType(ImageType.Format.MP4)))
        );
        String noMatchUrls = getJpgUrls(noJpgImages);
        System.out.println("JPG URLs for No JPG Images: " + noMatchUrls); // 预期输出: No Match!
    }
}