Need to wait() Thread in EJB code

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_ - 11 Oct 2005 19:43 GMT

    I need to accept a request and then query two systems. I need to send
off the first query to a queue then execute the second query. After
getting the result from the second query I need to wait for a response
from the first query via an MDB before combining the data from both
queries and returning a response.

    Of course the first thing about EJBs is that you can't muck around
waiting and notifying threads so how can I do this.

    Options

    Some JBoss specific classes that are safe to use. But I'll want to
move to WebSphere next year.

    Implement this as a separate stand-alone non-J2EE server.

    Use some J2EE API designed for this purpose. Am I missing this?

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Jon Martin Solaas - 12 Oct 2005 19:25 GMT

> I need to accept a request and then query two systems. I need to
> send off the first query to a queue then execute the second query.
[quoted text clipped - 13 lines]
>
> Use some J2EE API designed for this purpose. Am I missing this?

Put the result from the second query into a buffer and pick it up when
your MDB is triggered by the result of the first query.

The buffer could be anything from a singleton to a database table,
depending on lots of things that I don't know anything about :-) Anyway,
I don't think you have to write stuff that breaks portability and the
J2EE standard to achieve this. Just make sure the buffer won't become a
bottleneck.

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jon martin solaas

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_ - 12 Oct 2005 20:40 GMT

Thanks for the suggestion Jon. One of my main objectives is to devise
a solution that works inside the J2EE container. Your solution does
work for a setup where a client is sending queries and concurrently
listening for responses to past queries. Unfortunately I also have the
situation where the initial request thread is fired up by an HTTP
request and so needs to wind up by building a response and returning
that to the browser. I also don't know which query will finish first.
Any ideas?

>> I need to accept a request and then query two systems. I need to
>> send off the first query to a queue then execute the second query.
[quoted text clipped - 22 lines]
> J2EE standard to achieve this. Just make sure the buffer won't become a
> bottleneck.

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Need to wait() Thread in EJB code

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