使用Java在Eclipse中读取JSON文件时获取空值 [英] Getting null values when reading in JSON file in eclipse using java
问题描述
我正在读取放入项目文件夹中的JSON文件.我没有收到文件不存在的错误,并且在添加该行以忽略未知值之前,我遇到了错误.因此,我很确定它正在读取值.我遇到的问题是,当我尝试从JSON文件中打印出变量时,我得到了空值.
I am reading in a JSON file that I put in my project folder. I am not getting an error that the file doesn't exist and before I added the line to ignore unknown values I was getting errors. So I am pretty sure it is reading values in. The problem I am having is when I try to print out variables from the JSON file I get null values.
File jsonFile = new File("FoodItemData.json");
FoodItemData food = null;
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
try {
food = mapper.readValue(jsonFile, FoodItemData.class);
System.out.println(food.getcountry());
System.out.println(food.getId());
System.out.println(food.getDescription());
System.out.println(food.getcountry());
System.out.println(food);
} catch (JsonParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JsonMappingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(food.getcountry());
我调用FoodItemData类,并且所有获取的返回null.
I call the class FoodItemData and it returns null for all the gets.
public class FoodItemData{
private String country;
private String category;
private String description;
private String id;
private String name;
private String price;
public String getcountry(){
return this.country;
}
public void setcountry(String country){
this.country = country;
}
public String getCategory(){
return this.category;
}
public void setCategory(String category){
this.category = category;
}
public String getDescription(){
return this.description;
}
public void setDescription(String description){
this.description = description;
}
public String getId(){
return this.id;
}
public void setId(String id){
this.id = id;
}
public String getName(){
return this.name;
}
public void setName(String name){
this.name = name;
}
public String getPrice(){
return this.price;
}
public void setPrice(String price){
this.price = price;
}
}
这是我的JSON文件
{ "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"
}
]
}
我在做什么错了?
推荐答案
正如@Jonathan指出的那样,实际上在 FoodItemData.json
文件中没有对象,而是实际上具有了 Map
,其中包含单个键和一个数组作为值.因此,为了读取文件的内容,您可以做的最简单的操作(使用 Gson
lib com.google.gson.Gson
):
As @Jonathan pointed out instead of having an object inside of FoodItemData.json
file you actually have a Map
with single key and an array as value. So the minimum what you can do is this (using Gson
lib com.google.gson.Gson
) in order to read the content of the file:
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(new File("./FoodItemData.json")));
Map<String, List<FoodItemData>> object = (new Gson()).fromJson(reader, new TypeToken<Map<String, List<FoodItemData>>>(){}.getType());
List<FoodItemData> data;
if (object.values().iterator().hasNext()){
data = object.values().iterator().next(); // this is you data in your case 3 FoodItemData entries
}
} catch (FileNotFoundException e) {
....
}finally{
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
....
}
}
}
还请注意,一旦执行此操作,因为在json文件所在的国家/地区以-
开头,它将不会进入
Also note that once you do this, because in your json file country starts with -
it will not get in
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