使用 gson 将嵌套的 Java 对象与 json 进行转换

Question

假设我们有以下两个 Java 类（省略其他类成员）：

class Book {
    private String name;
    private String[] tags;
    private int price;
    private Author author;
}

class Author {
    private String name;
}

此外，假设我们有以下 json 对象：

{"Book": {
    "name": "Bible",
    "price": 20,
    "tags": ["God", "Religion"],
    "writer": {
        "name": "Jesus"
    }
}

我正在尝试找到将 Java Book 实例转换为 json 并使用 gson 转换回来的最佳方法。为了使示例更有趣，请注意在 json 中，我想使用“writer”而不是“Author”。你能帮忙吗？理想情况下，我希望看到一个完整的实现。

Answer 1

感谢您的所有回答。我能够弄清楚它并使用一些自定义序列化器和反序列化器来实现它。这是我自己的解决方案：

public class JsonTranslator {
    private static Gson gson = null;

    public void test(Book book1) {
        JsonElement je = gson.toJson(book1);  // convert book1 to json
        Book book2 = gson.fromJson(je, Book.class); // convert json to book2
        // book1 and book2 should be equivalent
    }

    public JsonTranslator() {

        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeAdapter(Book.class, new BookTrnaslator());
        builder.registerTypeAdapter(Author.class, new AuthorTrnaslator());
        builder.setPrettyPrinting();
        gson = builder.create();
    }


    private class BookTrnaslator implements JsonDeserializer<Book>, JsonSerializer<Book> {
        public Card deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
            JsonObject jobj = json.getAsJsonObject();
            Book book = new Book();
            book.setName(jobj.get("name").getAsString());
            book.setTags(jobj.get("tags").getAsJsonArray()); //Assuming setTags(JsonArray ja) exists
            book.setName(jobj.get("price").getAsInt());
            book.setAuthor(gson.fromJson(jobj.get("writer"), Author.class));
            return book;
        }

       public JsonElement serialize(Book src, Type typeOfSrc, JsonSerializationContext context) {
            JsonObject jobj = new JsonObject();
            jobj.addProperty("name", src.getName());
            jobj.add("tags", src.getTagsAsJsonArray());
            jobj.addProperty("price", src.getPrice());
            jobj.add("writer", gson.toJson(src.getAuthor()));
            return jobj;
       }
    }

    private class AuthorTrnaslator implements JsonDeserializer<Author>, JsonSerializer<Author> {
        public Card deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
            JsonObject jobj = json.getAsJsonObject();
            Author author = new Author();
            author.setName(jobj.get("name").getAsString());
            return author;
        }

       public JsonElement serialize(Author src, Type typeOfSrc, JsonSerializationContext context) {
            JsonObject jobj = new JsonObject();
            jobj.addProperty("name", src.getName());
            return jobj;
       }
    }
}

Answer 2

尝试使用 GsonBuilder#setPrettyPrinting() 配置 Gson 以输出适合页面以进行漂亮打印的 Json。此选项仅影响 Json 序列化。

阅读更多关于 Gson 的信息，它通常通过首先构造一个 Gson 实例然后在其上调用以下方法来使用。

• toJson(Object) 将指定对象序列化为其等效的 Json 表示形式。

• fromJson(String, Class)将指定的Json反序列化为指定类的对象。

---

BookDetails 对象到 JSON 字符串

示例代码：

Book book = new Book();
book.setName("Bible");
book.setTags(new String[] { "God", "Religion" });
book.setPrice(20);
Author author = new Author();
author.setName("Jesus");
book.setWriter(author);

BookDetails bookDetails = new BookDetails();
bookDetails.setBook(book);

String jsonString = new Gson().toJson(bookDetails);
// JOSN with pretty printing
// String jsonString = new GsonBuilder().setPrettyPrinting().create().toJson(bookDetails);
System.out.println(jsonString);

输出：

{"Book":{"name":"Bible","tags":["God","Religion"],"price":20,"writer":{"name":"Jesus"}}}

JSON 字符串到 BookDetails 对象

BookDetails newBookDetails = new Gson().fromJson(jsonString, BookDetails.class);

---

这是课程

class BookDetails {
    private Book Book;
    // getter & setter
}

class Book {
    private String name;
    private String[] tags;
    private int price;
    // Variable name should be writer instead of author as mapped to JSON string
    private Author writer; 
    // getter & setter
}

class Author {
    private String name;
    // getter & setter
}