solving NullPointerException in JAVA for a URL request

Question

So I am making a URL request to fetch a stream of data into a BufferedReader. The data that I am fetching has values "null" for various fields. The while condition I am using to read all the data is:

while (((inputLine = in.readLine()) != null))

so the condition is breaking in between, when it encounters a null value, which is actually not the EOF but only a field value. How do I resolve this?

Please show the exact stack trace you get. A BufferedReader cannot contain null values. — Martin v. Löwis
– Martin v. Löwis, Commented Dec 27, 2010 at 12:39
More detail please. Function calling list of where the exception originate from? To do this put a try catch block around the code and in the catch, catch this exception and get some information about where the exception was thrown to be able to answer the question: was the exception thrown from by the Java system by using a null value in your code or from the library code? — therobyouknow
– therobyouknow, Commented Dec 27, 2010 at 12:41
+1 @Martin v. Löwis beat me to it! yours is more succinct advice for @wishy ! — therobyouknow
– therobyouknow, Commented Dec 27, 2010 at 12:42

Jon Skeet · Accepted Answer · 2010-12-27 12:39:19Z

6

When you read a line, it will never be null until it reaches the end of the data. If there's no data in the line, it will just be an empty string instead.

You haven't shown enough code to explain why you're getting a NullPointerException, but you really need to understand that you won't see any "null values" before reaching the end of the data.

To work out why you're getting a NullPointerException:

Look at the line indicated in the stack trace
Identify every dereferencing operation
Either put a breakpoint on that line, or add some logging, or split the line into multiple statements so that each statement only has a single dereferencing operation

That should let you work out exactly which value is null, causing the exception to be thrown. What you need to do to fix it will depend on what you're trying to do and which value is null - we don't have enough information to help you on that front at the moment.

answered Dec 27, 2010 at 12:39

Jon Skeet

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4 Comments

wishy Over a year ago

Apologies for not framing the question correctly..!! The NullPointerException is being thrown at: String s_i = jobj1.get("id").toString(); , where jobj1 is a JSONObject and the value of "id" is null

Jon Skeet Over a year ago

@wishy: The value of "id" will never be null - it's a string literal. The return value of get("id") may well be null though, in which case that's clearly the problem... but that gives us no idea of how you want to proceed when it is null.

wishy Over a year ago

yea, I was getting confused. A simple NullPointException handling mechanism worked. I again apologise for not being clear in my query.

Jon Skeet Over a year ago

@wishy: Do you mean you're catching NullPointerException? That's almost never the right thing to do. Instead, call jobj1.get("id") and store the results in a variable, then test whether the value is null before you try to call toString.

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