解析Json数组导致这不是JSON数组例外(Parsing Json Array resulting in This is not a JSON Array exception)
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.
{
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
您的JSON在根目录中包含一个名为 FoodItemData $ c的JSON对象$ C>。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。