如何使用Jackson解析大的嵌套JSON文件？

Question

我正在Spring上開發Web API，它應該能夠提供端點並基於從JSON文件讀取的數據提供相關信息。 但是我用傑克遜反序列化嵌套的JSON文件時遇到問題。

我創建了Book類，並嘗試將JSON映射到HashMap以保留這些對象。 但是JSON文件具有比我想要的數據更多的數據，並且它像'volumeInfo'一樣嵌套。

class Book {

    private String isbn;
    private String title;
    private String subtitle;
    private String publisher;
    private long publishedDate;
    private String description;
    private int pageCount;
    private String thumbnailUrl;
    private String language;
    private String previewLink;
    private double averageRating;
    private String[] authors;
    private String[] categories;

// getters and setters

data.json文件樣本

{
 "requestedUrl": "https://www.googleapis.com/books/v1/volumes?q=java&maxResults=40",
 "items": [
  {
   "kind": "books#volume",
   "id": "7tkN1CYzn2cC",
   "etag": "pfjjxSpetIM",
   "selfLink": "https://www.googleapis.com/books/v1/volumes/7tkN1CYzn2cC",
   "volumeInfo": {
    "title": "A Hypervista of the Java Landscape",
    "publisher": "InfoStrategist.com",
    "industryIdentifiers": [
     {
      "type": "ISBN_13",
      "identifier": "9781592432172"
     },
     {
      "type": "ISBN_10",
      "identifier": "1592432174"
     }
    ],

  ]
}

我怎樣才能與Jackson取得那個volumeInfo？

Answer 1

您需要將其解析為JsonNode ，遍歷數組中的每個節點並轉換為Book ：

ObjectMapper mapper = new ObjectMapper();
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

JsonNode root = mapper.readTree(json); // read as JsonNode 
JsonNode items = root.at("/items");
List<Book> books = new ArrayList<>();
if (items.isArray()) {
    ArrayNode array = (ArrayNode) items;
    array.forEach(n -> {
        Book book = mapper.convertValue(n.get("volumeInfo"), Book.class); // convert to Book
        books.add(book);
    });
}
System.out.println(books);