Question about EJB 3.0

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cold80@libero.it - 07 Feb 2007 17:14 GMT

Just to understand better...I'm studying EBJ 3.0, session beans,
entities and JBoss to write web and distribuited applications for my
University coruse of Web Architecture. I'm studying a lot of
documentation and as a reference I'm reading the book "Mastering EJB
4th Edition". The problem is I can't understand the goal of
entities...I mean...am I supposed to use them always in the same VM
that is hosting the sessions beans, my jsp pages and servlets? Because
if I want to develop a client application that use the session beans
in order to interact with the server I need to let the entities
serializable and I have to give the .class files of the entities to
the client too! And this is not very good because if I change these
entities I'm supposed to deploy the new .class files to all the
clients...

I hope I made myself clear

Thanks in advance for your help

Cold

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Per Newgro - 08 Feb 2007 07:38 GMT

Hallo cold80@libero.it,

i hth to understand
http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/EJBConcepts4.html

Cheers
Per

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cold80@libero.it - 08 Feb 2007 08:07 GMT

Still it doesn't answer to my question...I understand that an entity
bean can be shared beetween different clients, but if I have to change
something in the database (and reflecting the changes on some
entities) I need to recompile these entitites and to deploy them to
all the users...this can be very annoying, don't you think? I mean,
maybe a better scenario is when I have a web application where all the
stuff is deployed in the same application server (therefore in the
same VM as well). Or am I not grabbing something about this
technology? Is that true that I have to deploy all the entities .class
files to all the clients every time I need to change something on my
data?

Thank you for your help

Cold

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Per Newgro - 08 Feb 2007 09:55 GMT

Hallo cold80@libero.it,

> Still it doesn't answer to my question...I understand that an entity
> bean can be shared beetween different clients, but if I have to change
[quoted text clipped - 7 lines]
> files to all the clients every time I need to change something on my
> data?

It depends. If your bean don't care about the datamodel (is generic) it's
not required. But normally yes (in bean for BMT or in deployment descriptor
for CMT). Do you change your data model periodically often? Otherwise if
you change it maybe 2 times a year the delivery of a new version seems not
a big problem to be for me.

There is a feature called hot deployment. This manages the new deployments
on customer side. So normally its enough to build a good installer without
restarting the server.

Cheers
Per

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Question about EJB 3.0

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