HttpSeesion.removeAttribute does not garbage collect object 2005-06-29 - By Partha Ranjan Das
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Hi J2EE Gurus,
We are having a seemingly peculiar problem.
In this case an activeX client makes multiple HTTP calls to a servelt in a web
server serially. The servlet has a single method to handle all these HTTP calls
(called "FP calls") . This method has many switch-case statements for these FP
calls. In the first "case" statement, it calls the EJB tier and gets a
collection of serializeable Value Object (Or Data Transfer Objects) and this
collection is maintained in the HttpSession by using HttpSession.setAttribute(
"XYZ",object). Now, when the following call, made by the same ActiveX client,
(in this FP series of calls) comes for the next FP call, it uses the collection
stored in session. The last FP call, after doing business operations, does
HttpSession.removeAttribute("XYZ"). So at this point, we assume that this
collection, which was so far bound to key "XYZ", should be ready for garbage
collection....right?
Wrong. When we ran JProfiler to find what all objects are there in the memory
at this point (after calling GC manually using the profiler),--- we find that
those objects, constituting that collection, which is supposed to be garbage
collected, are not at all garbage collected. What is more ashtonishing is that
we find half of these objects are lying in the EJB tier and half in the web
tier. But the servlet responds to all the FP calls and the ActiveX displays all
the information required. This means that the HTTP responses for all the HTTP
"FP call" requests have been duely and fully made.
Does anybody have any idea why, after calling session.removeAttribute also,
these objects are not garbage collected and also why half of these objects are
still lying in the EJB tier, even after EJB method has ended and GC is called
using the profiler? We are not maintaining this collection as a static
propoerty of any of the classes, either in web or EJB tier. We are using WSAD 5
.1.
Thanks in advance,
Regards,
Partha
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