Java BufferedReader value become null

Question

I'm using following code to get response from the API.

BufferedReader bf = new BufferedReader(new InputStreamReader(
                connection.getInputStream()));
        System.out.println("bf.readLine() - " + bf.readLine());

        output = bf.readLine();
        while (output != null) {
            JSONObject obj = new JSONObject(output);
            System.out.println("output is " + output);
            resCode = obj.getString("resCode");
            resDesc = obj.getString("COUNT");
        }

I can return bf.readLine() response as follows.

{"status":true,"data":[{"COUNT":"0"}]}

Problem is when I assign the bf.readLine() to String and check the value, it becomes null. Why bf.readLine() shows as null (gives null point exception) even it return the value from API.

What does the API say a `null` return value means? What does this mean in context of the code? — user2864740, Jun 16 '16 at 05:46
Every time you call `readLine()` it moves ahead. Once you run out of lines to read, `readLine()` returns null which causes the _NullPointerException_ . — Mihir, Jun 16 '16 at 05:46
I don't see where you would get an NPE, which line is giving you that? — matt, Jun 16 '16 at 05:49

score 4 · Answer 1 · edited May 23 '17 at 12:16

4

The reason is you are calling readLine twice. You calling first at System.out.println("bf.readLine() - " + bf.readLine()); and again at output = bf.readLine();

Modify as output = bf.readLine();System.out.println("bf.readLine() - " + output);

As per oracle docsreadLine()

Returns: A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached

if the end of the stream is reached then you will get null and operations on null will give nullpointerexception

edited May 23 '17 at 12:16

Community

1
1

answered Jun 16 '16 at 05:45

SpringLearner

13,738
20
78
116

could u please tell me where I have used twice? First one is for print the readLine value and second one for assign the value. is it a prolem – dmaprasad Jun 16 '16 at 05:50
bf.readline() is used twice this means you calling readline method twice – SpringLearner Jun 16 '16 at 05:52
Thank you very much. Problem solved according to your guidance. – dmaprasad Jun 16 '16 at 05:59

LONGHORN007 · Accepted Answer · 2016-06-16T06:36:11.770

1

Your code should be

BufferedReader bf = new BufferedReader(new InputStreamReader(
                connection.getInputStream()));

String output = null;

        while ((output = bf.readLine()) != null) {
         System.out.println("bf.readLine() value is--- - " + output );

            JSONObject obj = new JSONObject(output);
            System.out.println("output is " + output);
            resCode = obj.getString("resCode");
            resDesc = obj.getString("COUNT");
        }

edited Jun 16 '16 at 06:36

answered Jun 16 '16 at 05:48

LONGHORN007

526
9
24

Thanks for the code and helpful for solve the problem. But There should have brackets for output = bf.readLine() . Could you please edit that one. Then someone can directly use it. ((output = bf.readLine()) != null) instead of (output = bf.readLine() != null) – dmaprasad Jun 16 '16 at 06:06
Code is updated at your suggestion. Please read @SpringLearner answer to understand the flow and how i works – LONGHORN007 Jun 23 '16 at 03:57

Java BufferedReader value become null

2 Answers2