java - 使用 Gson 反序列化 JSON 时引用父对象

Question

给定以下 JSON:

{
    "authors": [{
        "name": "Stephen King",
        "books": [{
            "title": "Carrie"
        }, {
            "title": "The Shining"
        }, {
            "title": "Christine"
        }, {
            "title": "Pet Sematary"
        }]
    }]
}

这个对象结构:

public class Author {
    private List<Book> books;
    private String name;
}

public class Book {
    private transient Author author;
    private String title;
}

有没有办法使用 Google Java 库 Gson 反序列化 JSON 并且书籍对象具有对“父”作者对象的引用？

是否有可能不使用自定义解串器？

• 如果是:如何？
• 如果否:是否仍然可以使用自定义反序列化器来完成？

Answer 1

在这种情况下，我将为父对象实现自定义 JsonDeserializer，并传播 Author 信息，如下所示:

public class AuthorDeserializer implements JsonDeserializer<Author> {
    @Override
    public Author deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        final JsonObject authorObject = json.getAsJsonObject();

        Author author = new Author();
        author.name = authorObject.get("name").getAsString();

        Type booksListType = new TypeToken<List<Book>>(){}.getType();
        author.books = context.deserialize(authorObject.get("books"), booksListType);

        for(Book book : author.books) {
            book.author = author;
        }

        return author;
    }   
}

请注意，我的示例省略了错误检查。你会像这样使用它:

Gson gson = new GsonBuilder()
    .registerTypeAdapter(Author.class, new AuthorDeserializer())
    .create();

为了展示它的工作原理，我只从您的示例 JSON 中提取了“作者”键，允许我这样做:

JsonElement authorsJson  = new JsonParser().parse(json).getAsJsonObject().get("authors");

Type authorList = new TypeToken<List<Author>>(){}.getType();
List<Author> authors = gson.fromJson(authorsJson, authorList);
for(Author a : authors) {
    System.out.println(a.name);
    for(Book b : a.books) {
        System.out.println("\t " + b.title + " by " + b.author.name);
    }
}

打印的是:

Stephen King
     Carrie by Stephen King
     The Shining by Stephen King
     Christine by Stephen King
     Pet Sematary by Stephen King