servlet request.getParameterValues(fieldName) returns null and throw exception

Question

i want to get parameters values and sometimes i do not send them and it return me null and its ok . but when i preform check on the return string array the servlet throws a java.lang.NullPointerException

and i just what to do nothing when its null. ( continue the flow )

String[] values = null; 
if(request.getParameterValues(fieldName).length>0)
{
    values = request.getParameterValues(fieldName);

    if(null!=values || values.length>0) // HERE IT throws NullPointerException 
    {
        Collections.addAll(strlist, values);
    }
}

score 6 · Accepted Answer · answered Apr 29 '13 at 07:45

6

It should be

if(null!=values && values.length>0)

because, if your values is null(evaluating to false), the OR condition in your statement, executes the other part of the OR, which throws the NPE.

If you give an && there, it'll SHORT-CIRCUIT the statement evaluation when it encounters a false at null!=values.

answered Apr 29 '13 at 07:45

Rahul

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why , i what to check or this or that condition – user63898 Apr 29 '13 at 07:47
@user63898 If you check using OR, then although `values` is null, you'll still do `values.length` which will throw NPE. If you have `&&`, if `values` is null, the second part won't be checked since `false && no_matter_what` is always false. – Maroun Apr 29 '13 at 07:49
You can't do that. If you do it, then you're bound to get that exception! If values is `null`, `null.length` is bound to give you `NPE`. – Rahul Apr 29 '13 at 07:50

score 1 · Answer 2 · answered Apr 29 '13 at 07:48

1

It's the AND && operator that should be used to test if both conditions are met, which is what you need in you instance.

if (null != values && values.length > 0)

answered Apr 29 '13 at 07:48

blackpanther

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score 0 · Answer 3 · edited May 23 '17 at 12:04

0

in and unlike or if values is null it wont go for next check.

if(null!=values && values.length>0) // change to and 
 {
         Collections.addAll(strlist, values);
 }

also refer && (AND) and || (OR) in IF statements

edited May 23 '17 at 12:04

Community

1
1

answered Apr 29 '13 at 07:45

Suresh Atta

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score 0 · Answer 4 · answered Apr 29 '13 at 07:54

&& and || follow short-circuit evaluation.

That is these operators wont execute right side expressions if not needed.

for && operator if false at LHS, then it wont execute next expressions
for || operator if true at LHS, then it wont execute next expressions

so for your condition check it needs && operation for avoiding NullPointerException

if(null!=values && values.length>0)

servlet request.getParameterValues(fieldName) returns null and throw exception

4 Answers4