使用 json-simple 解析 Java 中的 JSON 文件

Question

I have created a.json file:

{
  "numbers": [
    {
      "natural": "10",
      "integer": "-1",
      "real": "3.14159265",
      "complex": {
        "real": 10,
        "imaginary": 2
      },
      "EOF": "yes"
    }
  ]
}

and I want to parse it using Json Simple, in order to extract the content of the "natural" and the "imaginary".

This is what I have written so far:

JSONParser parser = new JSONParser();
Object obj = parser.parse(new FileReader("...")); //the location of the file
JSONObject jsonObject = (JSONObject) obj;
String natural = (String) jsonObject.get("natural");
System.out.println(natural);

The problem is that the value of natural is "null" and not "10". Same thing happens when I write jsonObject.get("imaginary").

I have looked at many websites (including StackOverflow), I have followed the same way most people have written, but I am unable to fix this problem.

Answer 1

You need to find the JSONObject in the array first. You are trying to find the field natural of the top-level JSONObject , which only contains the field numbers so it is returning null because it can't find natural .

To fix this you must first get the numbers array.

Try this instead:

JSONParser parser = new JSONParser();
Object obj = parser.parse(new FileReader("...")); //the location of the file
JSONObject jsonObject = (JSONObject) obj;
JSONArray numbers = (JSONArray) jsonObject.get("numbers");

for (Object number : numbers) {
    JSONObject jsonNumber = (JSONObject) number;
    String natural = (String) jsonNumber.get("natural");
    System.out.println(natural);
}

Answer 2

The object in your file has exactly one property, named numbers .
There is no natural property.

You probably want to examine the objects inside that array.

Answer 3

Adding on to @Jermey Hanion's answer and comment, here is what I did to get "imaginary" and "natural"

JSONParser parser = new JSONParser();
Object obj = parser.parse(new FileReader("...")); //the location of the file
JSONObject jsonObject = (JSONObject) obj;
JSONArray numbers = (JSONArray) jsonObject.get("numbers");

for (Object number : numbers) {
    JSONObject jsonNumber = (JSONObject) number;
    String natural = (String) jsonNumber.get("natural");
    JSONObject complex = (JSONObject) jsonNumber.get("complex");
    String imaginary = (String) complex.get("imaginary");
    System.out.println(natural);
}

Jeremey's answer for getting imaginary is not correct, or maybe it was correct. The above snippet is to my knowledge working on my project.

PS. Sorry for reviving the thread but I thought it would be a useful resource for people looking to learn JSON.simple