Question on HttpSession

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posted 19 years ago

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Consider the following JSP code
What will it print for the very first request to this page as well as the web application that contains this page?

<html><body>
<%
Integer count = (Integer) request.getSession(false).getAttribute("count");
if(count != null )
{
out.println(count);
}
else request.getSession(false).setAttribute("count", new Integer(1));
%>
Hello!
</body></html>

Given answer: It will print Hello and will set the count attribute in the session.

According to me, since the parameter to request.getSession() is false in both the if and else clause(s), a session will not be created at all.
Shouldn't it throw a NullPointerException?

David Bridgewater

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posted 19 years ago

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Without trying the code... I think you will get a session by default. Unless you explicitly set a page directive in the JSP to say session="false", then the very beginning of the generated _jspService() method will obtain a session object. So when you use request.getSession(false) later in the code, there will be a session object there.

I'll try the code out now!

HTH,

David.

Jingh Yi

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posted 19 years ago

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Kedar,

I don't quite get your code snippet. Does the count attribute get set in the session somewhere else before you access it from jsp page?

Thanks,
Jenny

sawan parihar

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posted 19 years ago

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Hi,
The answer is correct it will print hello. This is because the implicit session object will be present and because of that it won't throw NullPointerException.

On the other hand if you include "<%@page session="false"%>" in your jsp then we are saying that not to make the implicit session object available and that's why in this case it will throw NullPointerException.

Hope this helps.

Sawan SCJP,SCWCD,SCBCD Every exit is an entry somewhere.

amit taneja

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posted 19 years ago

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so in this code... if we don't include this "<%@page session="false"%>
will it put session automatically even the page is viewed v.first time ?

how does it work is it like it will create a newsession before the page code runs and
when we reach the line request.getSession(false) ..
it will return only previos session and don't create new session...

so here the implicit session created is used with code getAttribute("count"); and as there is no "count" element ...it returns null

so no runtime error... is my understanding is right ?

pls reply

Thanks and Regards, Amit Taneja

sawan parihar

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posted 19 years ago

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so in this code... if we don't include this "<%@page session="false"%>
will it put session automatically even the page is viewed v.first time ?

Yes

so here the implicit session created is used with code getAttribute("count"); and as there is no "count" element ...it returns null so no runtime error... is my understanding is right

Yes you are right. When the page is visited first time the implicit object will be made available and request.getSession(false) will return the session object.

Hope it helps.

Sawan SCJP,SCWCD,SCBCD Every exit is an entry somewhere.