org.json.JSONException: JSONObject["userId"]没有找到。.JSONException

Question

现在我遇到了问题，就是json对象找不到密钥，我不知道为什么。但是，正如您在错误中看到的那样，响应是用所有键打印出来的。

package com.ar.team.company.project;

import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class Main {

    public static void main(String[] args) {
        try {
            Main.readJsonData();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void readJsonData() throws Exception {
        // Initializing:
        String url = "https://jsonplaceholder.typicode.com/posts/1"; // Our url.
        URL obj = new URL(url); // Our url object(To open connection from it.).
        HttpURLConnection con = (HttpURLConnection) obj.openConnection(); // Our 
        httpURLConnection to connect to json.
        // Optional default is GET for getting the data:
        con.setRequestMethod("GET");
        // Add request header:
        con.setRequestProperty("User-Agent", "Mozilla/5.0");
        // Getting the response code:
        int responseCode = con.getResponseCode();
        // Show to user the data:
        System.out.println("Sending 'GET' request to URL: " + url);
        System.out.println("Response code: " + responseCode);
        // Start read the data:
        BufferedReader in = new BufferedReader(new                         
        InputStreamReader(con.getInputStream())); // Our buffered reader.
        String inputLine; // For checking the new line.
        StringBuilder response = new StringBuilder(); // Here is our reading data.
        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine); // Append the data for response(StringBuilder).
        }
        in.close(); // Closing the buffered reader.
        // Print in String:
        System.out.println("The response data: " + response);
        // Read JSON response and print:
        JSONObject myResponse = new JSONObject(response);
        System.out.println("Result After Reading JSON Response:".toUpperCase());
        // All Result:
        System.out.println("UserId: " + myResponse.getString("userId"));
        System.out.println("Id: " + myResponse.getString("id"));
        System.out.println("Title: " + myResponse.getString("title"));
        System.out.println("Body: " + myResponse.getString("body"));
    }

}

误差

Sending 'GET' request to URL: https://jsonplaceholder.typicode.com/posts/1
Response code: 200
The response data: {  "userId": 1,  "id": 1,  "title": "sunt aut facere repellat 
provident occaecati excepturi optio reprehenderit",  "body": "quia et suscipit\nsuscipit 
recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas 
totam\nnostrum rerum est autem sunt rem eveniet architecto"}
RESULT AFTER READING JSON RESPONSE:
org.json.JSONException: JSONObject["userId"] not found.
   at org.json.JSONObject.get(JSONObject.java:516)
   at com.ar.team.company.project.Main.readJsonData(Main.java:48)
   at com.ar.team.company.project.Main.main(Main.java:14)

Answer 1

代码中的错误：

1. Error: JSONException: JSONObject["userId"] not found.

response是一个StringBuilder，所以new JSONObject(response)正在调用JSONObject(Object bean)构造函数。因为StringBuilder不是Java，所以它没有属性，而且JSONObject是空的。

将代码更改为new JSONObject(response.toString())，因此它称为JSONObject(String source) JSONObject(String source)

1. Error: JSONException: JSONObject["userId"] not a string.

userId的值是一个JSON数字，所以您必须调用一个get方法来检索一个数值，例如getInt(String key)，或者任何其他方法：getLong、getBigInteger、getDouble、getFloat、getNumber。

将代码更改为getInt("userId").

1. Error: JSONException: JSONObject["id"] not a string.

与#2相同:将代码更改为getInt("id").