Question

我正在尝试解析一个看起来像这样的Json数组：

{
  "FoodItemData": [
      {
        "country": "GB",
        "id": "100",
        "name": "Steak and Kidney Pie",
        "description": "Tender cubes of steak, with tender lamb kidney is succulent rich gravy.  Served with a side of mashed potatoes and peas.",
        "category": "Dinner",
        "price": "15.95"
      },
      {
        "country": "GB",
        "id": "101",
        "name": "Toad in the Hole",
        "description": "Plump British Pork sausages backed in a light batter.  Served with mixed vegetables and a brown onion gravy.",
        "category": "Dinner",
        "price": "13.95"
      },
      {
        "country": "GB",
        "id": "102",
        "name": "Ploughmanâ€™s Salad",
        "description": "Pork Pie, Pickled Onions, Pickled relish Stilton and Cheddar cheeses and crusty French bread.",
        "category": "Lunch",
        "price": "10.95"
      }
]
}

我正在使用Gson来解析这个Json。

URL url = getClass().getClassLoader().getResource("FoodItemData.json");

        FileReader fileReader = null;
        try {
            fileReader = new FileReader(url.getPath());
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        JsonReader jsonReader = new JsonReader(fileReader);
        Gson gson = new Gson();
        JsonParser parser = new JsonParser();
        JsonArray Jarray = parser.parse(jsonReader).getAsJsonArray();

        List<FoodItem> listOfFoodItems = new ArrayList<FoodItem>();

        for (JsonElement obj : Jarray) {
            FoodItem foodItem = gson.fromJson(obj, FoodItem.class);
            listOfFoodItems.add(foodItem);
        }

此代码导致java.lang.IllegalStateException: This is not a JSON Array异常。 FoodItem类包含与Json中名称相同的变量。

public class FoodItem {
    private String id;
    private String name;
    private String description;
    private String category;
    private String price;
    private String country;
}

我在这里遗漏了什么？我尝试使用this answer中给出的以下代码，但我得到了与该问题中提到的相同的异常。任何帮助将不胜感激。

Gson gson = new GsonBuilder().create();
Type collectionType = new TypeToken<List<FoodItem>>(){}.getType(); 
List<FoodItem> foodItems = gson.fromJson(jsonReader, collectionType);

Answer 1

您需要更改此

JsonArray Jarray = parser.parse(jsonReader).getAsJsonArray();

到

JsonArray Jarray = (JsonArray) parser.parse(jsonReader).getAsJsonObject().get("FoodItemData");

您的JSON在根目录中包含一个名为FoodItemData的JSON对象。该元素包含您尝试映射到List<FoodItem>

的JSON数组

或者，您可以创建一个名为FoodItemData的字段为List<FoodItem>

的字段

public class RootElement {
    List<FoodItem> FoodItemData;
    // the good stuff
}

并解析如此

RootElement root = gson.fromJson(jsonReader, RootElement.class);
System.out.println(root.FoodItemData);

另请注意，Java约定规定变量名称应以小写字符开头。

Answer 2

正如@Sotirios正确提到的，您的JSON是一个包含数组的对象，而不是一个独立的数组。

我会做一些小改动（而不是施放，我会使用getAsJsonArray）：

 JsonArray Jarray = parser.parse(jsonReader).getAsJsonObject().getAsJsonArray("FoodItemData");

解析Json数组导致这不是JSON数组异常

2 个答案: