解析Json数组导致这不是JSON数组例外 [英] Parsing Json Array resulting in This is not a JSON Array exception

问题描述

  {
FoodItemData：[ 
 {
country：GB，
id：100，
name：Steak and Kidney Pie，
description ：嫩牛排块，嫩羔羊肉是多汁丰富的肉汁，配上土豆泥和豌豆的一面。，
类别：晚餐，
价格： 15.95
，
 {
country：GB，
id：101，
name：Toad in the Hole ，
描述：丰满的英国猪肉香肠以浅色面糊为背景，配以混合蔬菜和棕色洋葱肉汁。，
类别：晚餐，
价格：13.95
}，
 {
country：GB，
id：102，
name： Ploughman's Salad，
description：猪肉馅饼，腌洋葱，腌制的Stilton和切达干酪，
类别：午餐，
价格：10.95
} 
] 
} 
  

我使用 Gson 来解析这个Json。

  URL url = getClass（）。getClassLoader（）。getResource（FoodItemData.json）; 
 
 FileReader fileReader = null; 
尝试{
 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（）; 
 
列表< FoodItem> listOfFoodItems = new ArrayList< FoodItem>（）; （JsonElement obj：Jarray）
 
 {
 FoodItem foodItem = gson.fromJson（obj，FoodItem.class）; 
 listOfFoodItems.add（foodItem）; 
} 
  

此代码导致 java.lang.IllegalStateException：这不是JSON数组异常。 FoodItem 类包含与Json中相同名称的变量。

  public class FoodItem {
 private String id; 
私人字符串名称; 
私有字符串描述; 
私有字符串类别; 
私人字符串价格; 
私人字符串国家; 
} 
  

我在这里遗漏了什么吗？我尝试使用中给出的以下代码答案，但我得到了与该问题中提到的例外相同的例外。任何帮助将不胜感激。

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

解决方案

您需要更改这个

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

至

 <$ jsonArray Jarray =（JsonArray）parser.parse（jsonReader）.getAsJsonObject（）。get（FoodItemData）; 
  

您的JSON在根目录中包含一个名为 FoodItemData 。该元素包含您试图映射到 List< FoodItem>

的JSON数组或者，您可以创建一个名为 FoodItemData 的字段，它是一个 List< FoodItem>

  public class RootElement {
 List< FoodItem> FoodItemData; 
 //好东西
} 
  

像这样解析

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

---

另外请注意，Java约定规定变量名应该以小写字母开始。

I am trying to parse a Json array which looks like this:

{
  "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": "Ploughman’s Salad",
        "description": "Pork Pie, Pickled Onions, Pickled relish Stilton and Cheddar cheeses and crusty French bread.",
        "category": "Lunch",
        "price": "10.95"
      }
]
}

I am using Gson to parse this 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);
        }

This code results in java.lang.IllegalStateException: This is not a JSON Array exception. The FoodItem class contains the variables with the same name as in the Json.

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

Am I missing anything here? I tried using the following code as given in this answer, but I got the same exception as the one mentioned in that question. Any help would be appreciated.

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

解决方案

You will need to change this

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

to

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

Your JSON contains a JSON object at the root called FoodItemData. That element contains the JSON array you are trying to map to a List<FoodItem>

Alternatively, you could create a class that has a field called FoodItemData that is a List<FoodItem>

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

And parse like so

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

---

Also, note that Java convention states that variable names should start with a lower case character.

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