Why NumberFormatException?

[Jyoti Vaskar]

I have a jsp page in which I enter age.

I am getting the value from jsp into servlet by

age=Integer.parseInt(req.getParameter("age"));

But now while running I am getting exception of NumberFormatException

when I enter any value into text box of age and press add button of JSP.

Why is that?
Can anybody explain?

[Rahul P Kumar]

Possibly you need to trim the age string, as:

age=Integer.parseInt(req.getParameter("age").trim()); 

[Rahul P Kumar]

By the way, if you had taken stack trace, you yourself had figured it out the exact reason, or could have shown to us.

[Jyoti Vaskar]

thanks for the reply.

I have added trim() as you said & now its shocking

that I am getting a NullPointerException?? ??

I would like to know about stack trace.

I really don't know about it.

[Jyoti Vaskar]

I have sort out it.
It was the mistake made in jsp page where <form> tag was placed wrongly.

thank you for the help.

[Rahul P Kumar]

a null pointer exception shows, that no value is being passed from request.getParameter(). Another debugging method. Take

System.out.println(req.getParameter("age"))

in such cases. In your case it could have quickly shown that there is (no) value being passed. stack trace can be generated from inside catch block. Try searching Exception handling in google, if you are not aware of it.

[Jyoti Vaskar]

Rahul.p Kumar wrote: stack trace can be generated from inside catch block. Try searching Exception handling in google, if you are not aware of it.

I guess you are talking about try catch & finally blocks?

Or it may be System.out.println() about which I am aware of.

I guess stack trace is one & the same thing above, which I am aware of ?

By searching exception handeling I got the same result above !

[Rahul P Kumar]

yes both are pointing to same thing. you print stack trace in catch block. These are common debugging ways, you can use to quickly blame a piece of code

[Jyoti Vaskar]

Rahul.p Kumar wrote:yes both are pointing to same thing. you print stack trace in catch block. These are common debugging ways, you can use to quickly blame a piece of code

Then I am aware of stack trace.

thank you Rahul for the help .