[java] How do I parse JSON into an int?

I have Parsed some JSON data and its working fine as long as I store it in String variables.

My problem is that I need the ID in an int varibable and not in String. i have tried to make a cast int id = (int) jsonObj.get("");

But it gives an error message that I cannot convert an object to an int. So I tried to convert by using:

String id = (String) jsonObj.get("id");
int value = Integer.parseInt(id);

But also that is not working. What is wrong. How is JSON working with int? My strings are working just fine its only when I try to make them as an int I get problems.

Here is my code :

public void parseJsonData() throws ParseException {

        JSONParser parser = new JSONParser();
        Object obj = parser.parse(jsonData);
        JSONObject topObject = (JSONObject) obj;
        JSONObject locationList = (JSONObject) topObject.get("LocationList");
        JSONArray array = (JSONArray) locationList.get("StopLocation");
        Iterator<JSONObject> iterator = array.iterator();

        while (iterator.hasNext()) {

            JSONObject jsonObj = (JSONObject) iterator.next();
            String name  =(String) jsonObj.get("name");
            String id = (String) jsonObj.get("id");
            Planner.getPlanner().setLocationName(name);
            Planner.getPlanner().setArrayID(id);


        }

    }

At first, you create a BufferedReader on a FileReader to the file.

Then, you create a new `JSONParser()´ object that parses the content read from the file.

You cast the parsed Object to a JSONObject and get the id field.

FileReader file=new FileReader("1.json");
BufferedReader write=new BufferedReader(file);
Object obj=new JSONParser().parse(write);
JSONObject jo = (JSONObject) obj;
long id=(long)jo.get("id");

Its very simple.

Example JSON:

{
   "value":1
}

int z = jsonObject.getInt("value");

The question is kind of old, but I get a good result creating a function to convert an object in a Json string from a string variable to an integer

function getInt(arr, prop) {
    var int;
    for (var i=0 ; i<arr.length ; i++) {
        int = parseInt(arr[i][prop])
            arr[i][prop] = int;
    }
    return arr;
  }

the function just go thru the array and return all elements of the object of your selection as an integer

Non of them worked for me. I did this and it worked:

To encode as a json:

JSONObject obj = new JSONObject();
obj.put("productId", 100);

To decode:

long temp = (Long) obj.get("productId");

It depends on the property type that you are parsing.

If the json property is a number (e.g. 5) you can cast to Long directly, so you could do:

(long) jsonObj.get("id") // with id = 5, cast `5` to long 

After getting the long,you could cast again to int, resulting in:

(int) (long) jsonObj.get("id")

If the json property is a number with quotes (e.g. "5"), is is considered a string, and you need to do something similar to Integer.parseInt() or Long.parseLong();

Integer.parseInt(jsonObj.get("id")) // with id = "5", convert "5" to Long

The only issue is, if you sometimes receive id's a string or as a number (you cant predict your client's format or it does it interchangeably), you might get an exception, especially if you use parseInt/Long on a null json object.

If not using Java Generics, the best way to deal with these runtime exceptions that I use is:

if(jsonObj.get("id") == null) {
   // do something here
}

int id;
try{
    id = Integer.parseInt(jsonObj.get("id").toString());
} catch(NumberFormatException e) {
  // handle here
}

You could also remove that first if and add the exception to the catch. Hope this helps.

I use a combination of json.get() and instanceof to read in values that might be either integers or integer strings.

These three test cases illustrate:

int val;
Object obj;
JSONObject json = new JSONObject();
json.put("number", 1);
json.put("string", "10");
json.put("other", "tree");

obj = json.get("number");
val = (obj instanceof Integer) ? (int) obj : (int) Integer.parseInt((String) obj);
System.out.println(val);

obj = json.get("string");
val = (obj instanceof Integer) ? (int) obj : (int) Integer.parseInt((String) obj);
System.out.println(val);

try {
    obj = json.get("other");
    val = (obj instanceof Integer) ? (int) obj : (int) Integer.parseInt((String) obj);
} catch (Exception e) {
    // throws exception
}

You may use parseInt :

int id = Integer.parseInt(jsonObj.get("id"));

or better and more directly the getInt method :

int id = jsonObj.getInt("id");