Android JSONObject getString method check for null/NULL?

Question

Hitting a brick wall in my code at the moment for fetching json objects from multiple pages(using a loop) in a AsyncTask. It reaches the last page, but getting the correct if statement to ensure that the loop DOESN'T run again and continues on is baffling me.

    String data = //some correct json data with next element that holds a uri parseable string
    JSONObject initial = new JSONObject(data);
    String next = initial.getString(nextObjSTR);
    //gonna start from the "last" page and recursively return to the 1st page
    if(*The if condition I need help with*) {
        //there is another page
        makeConnection(Uri.parse(next));
    }

Basically, the last page of json elements has a next element with a null or no element value, which triggers the IOException error caught in makeConnection method because my initial if statement has always been failing.

Can I get a reason or help as to the appropriate if check for Strings from json? I've tried String != null as NullPointerExceptions occur if I use any method from String to compare. Likewise, JsonObject.NULL comparison doesn't work for me either.

Put the code in a try block and catch the exception. Print exception details using logging and post them back here. That'll help us more. — Gurupad Mamadapur
– Gurupad Mamadapur, Commented Sep 11, 2016 at 11:02
Well, The data has to be null at some point, It works for the first 12 pages of data. Also, there is a try catch block in makeconnection that catches the error, so that is also irrelevant. — kthieu
– kthieu, Commented Sep 11, 2016 at 18:07
getString throws an exception when the key does not exist in the JSON. If the null-check isn't working, then you don't have a null value. You might have an empty string. — OneCricketeer
– OneCricketeer, Commented Sep 11, 2016 at 20:26

OneCricketeer · Accepted Answer · 2016-09-12 01:29:11Z

3

None of the other answers worked, and I ended up questioning whether the element was really null despite looking at the parsed json data via an online tool. In the end, JSONObject.IsNull(element mapping name) is the right approach.

edited Sep 12, 2016 at 1:29

OneCricketeer

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answered Sep 12, 2016 at 1:12

kthieu

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Comments

Sinh Phan · Accepted Answer · 2016-09-12 03:09:44Z

2

you must check value with key is has in json object. Try below code:

JSONObject initial = new JSONObject(data);
if(initial.has(nextObjSTR)) {
    String next = initial.getString(nextObjSTR);
    if (next != null && !next.isEmpty()) {
        makeConnection(Uri.parse(next));
    }               
}

answered Sep 12, 2016 at 3:09

Sinh Phan

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Comments

Artem Novikov · Accepted Answer · 2016-09-11 20:35:04Z

1

If you're sure that the value is either null (empty) or a correct URI, and assuming that the nextObjSTR key is always present in the data JSON, then that will do:

if (next != null && !next.trim().isEmpty()) {
   makeConnection(Uri.parse(next));
}

Or, since you're on Android, it's better use the more convenient method:

if (!TextUtils.isEmpty(next)) {
   makeConnection(Uri.parse(next));
}

answered Sep 11, 2016 at 20:35

Artem Novikov

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Comments

Quanten · Accepted Answer · 2016-09-11 20:43:20Z

1

You can use the optString Method of the JSONObject. If the JSON key is not this method will return a empty string, so you can check it easily:

String next = initial.optString(nextObjSTR);
if ( ! next.isEmpty() ) {
   makeConnection(Uri.parse(next));
}

Source: https://developer.android.com/reference/org/json/JSONObject.html#optString(java.lang.String)

edited Sep 11, 2016 at 20:43

answered Sep 11, 2016 at 20:20

Quanten

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1 Comment

Quanten Over a year ago

Sorry, I'm rather new in Java and not compared (or check if zero) yet. I've correct it

bsgdragao · Accepted Answer · 2020-09-13 04:43:03Z

0

I do like this...

String value; 
if(jsonObject.get("name").toString.equals("null")){
  value = "";
else{
   value = jsonObject.getString("name");
}

answered Sep 13, 2020 at 4:43

bsgdragao

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