java 用Java读取json文件
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Reading a json file in Java
提问by aze45sq6d
So I am having troubles with reading a Json file in Java.
所以我在用 Java 读取 Json 文件时遇到了麻烦。
It is a Json file with content in this format:
这是一个 Json 文件，内容格式如下：
{
"_id": 2864071,
"name": "Neustadt",
"country": "DE",
"coord": {
"lon": 12.56667,
"lat": 52.400002
}
}
This is the code I am using:
这是我正在使用的代码：
package controllers;
@Named(value = "cityID")
@SessionScoped
public class getCityIDs implements Serializable {
public long getCityIDs(String name) {
//Read the json file
try {
FileReader reader = new FileReader(filePath);
JSONParser parser = new JSONParser();
JSONObject jsonObject = (JSONObject) parser.parse(reader);
// get a number from the JSON object
String travelName = (String) jsonObject.get("name");
if(travelName.equals(name)){
long id = (long) jsonObject.get("_id");
System.out.println(id);
return id;
} else {
System.out.println("else");
return 0;
}
} catch (FileNotFoundException ex) {
Logger.getLogger(getCityIDs.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException | ParseException ex) {
Logger.getLogger(getCityIDs.class.getName()).log(Level.SEVERE, null, ex);
}
System.out.println("einde functie");
return 0;
// JSONObject jsonObject = (JSONObject) parser.parse(getClass().getResource("/json/city.list.json").toString());
}
public String test(){
return "hello world";
}
}
However, it gives me an error at this line:
但是，它在这一行给了我一个错误：
JSONObject jsonObject = (JSONObject) parser.parse(reader);
being:
存在：
Severe: Unexpected token LEFT BRACE({) at position 88.
at org.json.simple.parser.JSONParser.parse(Unknown Source)
at org.json.simple.parser.JSONParser.parse(Unknown Source)
at controllers.getCityIDs.getCityIDs(getCityIDs.java:45)
For some reason it can't read the filepath? "Unknown source"? I'm not sure what I'm doing wrong.
出于某种原因，它无法读取文件路径？“来源不明”？我不确定我做错了什么。
The method just returns a "0" when I call the method in another class, with as country name "Neustadt". Basically all I want is for this function to return the ID for a certain city. The names are stored in the Json, together with the ID.
当我在另一个类中调用该方法时，该方法仅返回“0”，国家名称为“Neustadt”。基本上我想要的就是让这个函数返回某个城市的 ID。名称与 ID 一起存储在 Json 中。
Edit:Ideally I want to be able to parse the JSON file, which is located inside the project. I tried using .getClass().getResource("/path/to/json"); but that didn't work at all.
编辑：理想情况下，我希望能够解析位于项目内的 JSON 文件。我尝试使用 .getClass().getResource("/path/to/json"); 但这根本不起作用。
EDIT: FIXED
编辑：固定
package controllers;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Serializable;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.enterprise.context.RequestScoped;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
@Named(value = "cityID")
@SessionScoped
public class getCityIDs implements Serializable{
JSONObject jsonObject;
public long getCityIDs(String name) {
try {
JSONParser parser = new JSONParser();
InputStream in = getClass().getResourceAsStream("/dataSteden/stedenNamen1.json");
try (BufferedReader br = new BufferedReader(new InputStreamReader(in))) {
String line;
while ((line = br.readLine()) != null) {
jsonObject = (JSONObject) parser.parse(line);
}
}
String travelName = (String) jsonObject.get("name");
System.out.println("stad: " +travelName);
System.out.println("testttt");
if(travelName.equals(name)){
long id = (long) jsonObject.get("_id");
System.out.println(id);
return id;
} else {
System.out.println("else");
return 5;
}
} catch (FileNotFoundException ex) {
Logger.getLogger(getCityIDs.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException | ParseException ex) {
Logger.getLogger(getCityIDs.class.getName()).log(Level.SEVERE, null, ex);
}
System.out.println("einde functie");
return 0;
// JSONObject jsonObject = (JSONObject) parser.parse(getClass().getResource("/json/city.list.json").toString());
}
public String test(){
return "hello world";
}
}
回答by OneCricketeer
Your data is line-delimited
您的数据以行分隔
{"_id":707860,"name":"Hurzuf","country":"UA","coord":{"lon":34.283333,"lat":44.549999}}
{"_id":519188,"name":"Novinki","country":"RU","coord":{"lon":37.666668,"lat":55.683334}}
{"_id":1283378,"name":"Gorkhā","country":"NP","coord":{"lon":84.633331,"lat":28}}
Therefore, you cannot throw the entire file into a JSONParser, you must read the file line-by-line and parse each line as a JSONObject, from which you can extract out the needed key-values.
因此，您不能将整个文件放入一个JSONParser，您必须逐行读取文件并将每一行解析为JSONObject，您可以从中提取出所需的键值。
