使用Java Streams高效过滤嵌套列表并提取数据

产品 A: {
    名称: a
    图片: [
      {
           图片ID: 1
           URL: url1
           类型: [
             { 格式: jpg },
             { 格式: png }
          ]
      },
      {
           图片ID: 2
           URL: url2
           类型: [
             { 格式: mp4 },
             { 格式: png }
          ]
      },
      {
           图片ID: 3
           URL: url3
           类型: [
             { 格式: jpg },
             { 格式: mp4 }
          ]
      }
    ]
}

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

// 定义图片格式枚举
enum Format {
    JPG, PNG, MP4;
}

// 定义图片类型类
class Type {
    private Format format;

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

    public Format getFormat() {
        return format;
    }

    @Override
    public String toString() {
        return "Type{" + "format=" + format + '}';
    }

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

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

// 定义图片类
class Image {
    private String imgId;
    private String url;
    private List<Type> types;

    public Image(String imgId, String url, List<Type> types) {
        this.imgId = imgId;
        this.url = url;
        this.types = types;
    }

    public String getImgId() {
        return imgId;
    }

    public String getUrl() {
        return url;
    }

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

    @Override
    public String toString() {
        return "Image{" + "imgId='" + imgId + '\'' + ", url='" + url + '\'' + ", types=" + types + '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Image image = (Image) o;
        return Objects.equals(imgId, image.imgId) && Objects.equals(url, image.url) && Objects.equals(types, image.types);
    }

    @Override
    public int hashCode() {
        return Objects.hash(imgId, url, types);
    }
}

// 定义产品类 (可选，如果仅处理图片列表则无需此层)
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;
    }

    @Override
    public String toString() {
        return "Product{" + "name='" + name + '\'' + ", images=" + images + '}';
    }
}

public class ImageProcessor {

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

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

    /**
     * 从图片集合中获取所有JPG格式图片的URL，并以逗号分隔返回。
     *
     * @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 getJpgImageUrls(final Collection<Image> images) {
        if (images == null || images.isEmpty()) {
            return "No Match!";
        }

        return images.stream()
                .filter(isJpgImage)            // 1. 过滤：筛选出包含JPG格式的图片
                .map(Image::getUrl)             // 2. 映射：将图片对象转换为其URL字符串
                .reduce(urlReducer)             // 3. 规约：将所有URL字符串用逗号连接
                .orElse("No Match!");           // 处理没有匹配项的场景
    }

    public static void main(String[] args) {
        // 示例数据
        List<Image> productAImages = Arrays.asList(
            new Image("img1", "url1", Arrays.asList(new Type(Format.JPG), new Type(Format.PNG))),
            new Image("img2", "url2", Arrays.asList(new Type(Format.MP4), new Type(Format.PNG))),
            new Image("img3", "url3", Arrays.asList(new Type(Format.JPG), new Type(Format.MP4)))
        );

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

        // 调用处理方法
        String jpgUrls = getJpgImageUrls(productA.getImages());
        System.out.println("JPG Image URLs for Product A: " + jpgUrls); // 预期输出: url1,url3

        // 另一个示例：所有图片都不含JPG
        List<Image> productBImages = Arrays.asList(
            new Image("img4", "url4", Arrays.asList(new Type(Format.PNG))),
            new Image("img5", "url5", Arrays.asList(new Type(Format.MP4)))
        );
        Product productB = new Product("b", productBImages);
        String jpgUrlsB = getJpgImageUrls(productB.getImages());
        System.out.println("JPG Image URLs for Product B: " + jpgUrlsB); // 预期输出: No Match!

        // 示例：空图片列表
        List<Image> emptyImages = Arrays.asList();
        String jpgUrlsEmpty = getJpgImageUrls(emptyImages);
        System.out.println("JPG Image URLs for Empty List: " + jpgUrlsEmpty); // 预期输出: No Match!
    }
}