Are implicit objects in JSP are thread safe???

[Murali Mohan]

Hi all,

Are implicit objects in JSP are thread safe???
Thanks,
Mohan
[ January 30, 2004: Message edited by: Murali Mohan ]

[David O'Meara]

Depends. For example the request, response and exception objects are created for the current thread and therefore they are safe. The application and session objects can be accessed by several threads and therefore not thread safe.

[Andres Gonzalez]

Session scope - Not thread safe
Context scope - Not thread safe
Request scope - thread safe (Only one thread per request)

[Frank Carver]

It's important to note, though, that if you store objects in the application, session, request or page contexts, they are not guaranteed to be thread safe.
Although the request and page objects themselves are threadsafe, objects stored in them are only safe if they are not also used by other threads. Remember that one of these contexts only stores a reference to an object, not a separate copy of it.
I hope that's not too confusing.

[bharat nagpal]

Frank,
Could you please explain in detail?
TIA

[Frank Carver]

I'll try.
If you create a completely new object in the method, and place it in the request context, it will be threadsafe:

<%
Integer ii = new Integer(25);
request.setAttribute("ii", ii);
%>

If you use an existing object which is also present in one of the unsafe contexts (application or session), it will not be threadsafe:

<%
Integer ii = (Integer)application.getAttribute("aii");
request.setAttribute("ii", ii);
%>

If you use an existing object which is a static (class) or member (instance) variable in the servlet class, it will not be threadsafe:

<%! 
 Integer ii = new Integer(25); // note the ! - it's member variable
<%
request.setAttribute("ii", ii);
%>

Is that any clearer?

[bharat nagpal]

yup.Thats very much clear now.
Thanks a lot