NullPointerException on creation of JSONArray

Question

I'm making a call to an API using Volley in my app. And the call to convert the String response to a JSONArray fails with a java.lang.NullPointerException.

I don't understand why there is a NullPointerException. I verified that I'm getting a response from the API so i should not be passing a null string to the JSONArray constructor. This is the code snippet. The exception occurs in the try-catch block.

String requestUrl = "https://api.trello.com/1/members/me/boards?key="+keys.apiKeyTrello+"&token="+savedToken;

StringRequest stringRequest = new StringRequest(Request.Method.GET, requestUrl, new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        // Display the first 500 characters of the response string.
        boardListView.setText("Response is: " + response);
        copyResponse = new String(response);
        Log.d("timer", "reached here");
    }
},
    new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            copyResponse = new String("[{\"error\":\"error\"}]");
            boardListView.setText("That didn't work!");
    }
});

queue.add(stringRequest);

try {
    JSONArray jsonArray = new JSONArray(copyResponse); // NullPointerException here
}
catch (JSONException e){
    //Handle exception
}

A sample response from the API is here: http://pastebin.com/Bs2GYPcC

The stacktrace is like so:

10-09 19:28:03.856 3535-3535/im.chaitanya.pomodorotimer E/AndroidRuntime: FATAL EXCEPTION: main
10-09 19:28:03.856 3535-3535/im.chaitanya.pomodorotimer E/AndroidRuntime: Process: im.chaitanya.pomodorotimer, PID: 3535
10-09 19:28:03.856 3535-3535/im.chaitanya.pomodorotimer E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{im.chaitanya.pomodorotimer/im.chaitanya.pomodorotimer.ShowBoardList}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
10-09 19:28:03.856 3535-3535/im.chaitanya.pomodorotimer E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)

may be your copyResponse is not initialized it going int to another thread you will get it on response or in error — Pavan, Oct 09 '15 at 14:05

score 3 · Accepted Answer · answered Oct 09 '15 at 14:07

The String request is executed asynchronously, so at the time you call the method inside the try - catch the variable is not yet initialised and it fails with a NullPointerException.

I suggest you move the code in the try catch to the onSuccess() and the onErrorResponse method. This way it will be called after you have received the response from the server.

score 1 · Answer 2 · answered Oct 09 '15 at 14:10

You initialize copyResponse in the onResponse method, so it is null before onResponse is called (asynchronous call).

If you try to parse your JSONArray in the onResponse method it should work. Something like :

@Override
public void onResponse(String response) {
    // Display the first 500 characters of the response string.
    boardListView.setText("Response is: " + response);
    //copyReponse is useless here. You can directly use response
    Log.d("timer", "reached here");
    try {
        JSONArray jsonArray = new JSONArray(response);
    }
    catch (JSONException e){
        //Handle exception
    }
}

NullPointerException on creation of JSONArray

2 Answers2