5 Replies Latest reply on Jan 10, 2004 5:18 AM by stefano_fornari

Detecting if a remote reference is still valid

stefano_fornari Jan 1, 2004 9:02 AM

Hi All EJB gurus,
I would need a help in sorting out this issue.

I have a fat client that gets a remote object and makes calls as it requires. It is a GUI driven application, so the user can also go away for a coffee. The EJB is a session EJB, thus in the meantime, the session may expire or more harmfully, the server crashes and restarts.
What happens then to my remote reference? I doubt it would be still valid. If it is invalid, is there a way to know that state? Or I have to catch the RemoteException and try a new lookup?

Many thanks in advance

Stefano

1. Re: Detecting if a remote reference is still valid

juha Jan 5, 2004 6:53 AM (in response to stefano_fornari)

If the server crashes the session state is gone, unless you implement your own persistence and recovery mechanism. Otherwise you have no choice but to recreate the session or set up a cluster with session failover.

Sessions are passivated to disk after a timeout, and eventually cleaned up from disk once they expire. Set the expiration value long enough for the user to return from their lunch (say 1 week), it's not using any server resources if the session is inactive (it's just sitting on the disk).
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2. Re: Detecting if a remote reference is still valid

milowe Jan 7, 2004 9:06 AM (in response to stefano_fornari)

And once again; you can check if your reference is valid by using getHandle() (will throw RemoteException if not valid).
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3. Re: Detecting if a remote reference is still valid

juha Jan 7, 2004 3:33 PM (in response to stefano_fornari)

Have you tried it? As far as I can remember getHandle() implementation doesn't try to connect to the server. You'd have to do getHandle().getEJBObject() at least. And that implies JNDI lookup and downloading a new proxy instance to the client so you really don't want to be doing that all over the place.
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4. Re: Detecting if a remote reference is still valid

milowe Jan 9, 2004 2:34 AM (in response to stefano_fornari)

A bit sloppy in my comment. Yes, I do use getEJBObject() on my Handle.
This solution works fine for me since this session is not accessed that frequently.
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5. Re: Detecting if a remote reference is still valid

stefano_fornari Jan 10, 2004 5:18 AM (in response to stefano_fornari)

Thanks to everybody.

Too bad there is not a standardized way. The getHandle().getObject() method is clever, but for my purpose overkilling. I prefere to add a business delegate that intercepts RMIException and handles it accordingly (getting a new object if necessary and possible).
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