James Cook wrote:
>
> I thought I would start a new thread, because I think Dan Benanev's original
> question has gotten buried.
>
> Description
> ============
> J2EE examples from SUN and Ed Roman's "Mastering Enterprise Javabeans"
> describe a technique whereby a servlet stores a handle to a stateful session
> bean in an HTTP session object. When an incoming request is received by the
> servlet, the handle to the bean is restored and communication with the
> stateful session bean recommences.
>
> Problem
> =======
> Servlet's are most often deployed in a manner that allows multiple web
> client requests to be handled by the same instance of a servlet. If the user
> has two browsers open and pointing to the same servlet, it is possible for
> two separate threads of execution in the servlet to attempt access to the
> same stateful session bean. This will generate an exception.
Please explain why you would get an exception here. Although the same
servlet instance may be used to service multiple concurrent clients, when
you rematerialize your EJB object reference from a handle, you should keep
the object reference in a 'local' variable, not a 'member' variable. Thus
any synchronization or thread-safety requirements shoould be avoided.
> Challenge
> =========
> Are the standard examples of accessing stateful session beans from servlets
> flawed? How does your product determine that a client request is actually
> coming from a distinct client? How would you recommend these situations be
> implemented?
>
> Discussion Point
> ================
> It seems to me that a servlet represents a web application and it is not
> *wrong* that the two browser windows (or two frames in a single window)
> share the same HTTP object, and thus, the same stateful session bean handle.
> I think what many examples fail to mention is that this EJB reference is a
> shared resource that must be synchronized. The "best practice" that I would
> choose to put forth would read:
>
> Access to a stateful session bean object from within any application that is
> multithreaded (i.e. servlets) must be synchronized to ensure only one thread
> is executing at a time.
>
> Dooohhh. Sounds a lot like the spec, no?
>
> thanks,
> jim
>
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Evan Ireland Sybase EA Server Engineering [EMAIL PROTECTED]
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