Very Basic Question in EJb

[Prashant Vasudeo]

This may be very basic question but...
Definition of ejb bj ed-roman says that..
"An ejb ia a server-side software component that can be deployed in a distributed multitier environment"
Now servlets is also a server-side component then what;s the difference in ejb.
(I know that container provides services to ejb...transaction ,persistence, security....)
and what is mean by "can be deployed in a distributed multitier environment"
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prashant

[Ajith Kallambella]

IMO one major difference is the divergence from simple request/response semantics. Unlike Servlets(having a single point of entry), EJBs can expose business methods and hence they are true "business components".
And then you have inbuilt transaction support, instance pooling, lifecycle management and other such goodies...

[Manish Kamat]

methods can be invoked remotely on distributed environment which is not possible with servlets.

[Dasun Perera]

A very good question though it is a basic one. As others also pointed out EJBs are true distributed objects which has lots of facilities provided by the container where as a Servlet is just an entry point to the web container.
But I think what you are asking is, Why EJBs when Servlets are there ?. If this is your question you are talking about most commonly asked EJB question. For most of the applications (As far as I believe) EJBs are not needed or at least the use of EJBs cannot be justified(interms of money and complexity). But there are some applications which needs transactions management like services and for such projects use of EJBs can be justified.

[Stan James]

There are a number of reasons EJBs might be useful in your architecture: They have the services of the container going for them: security, transactions, scalability, container managed persistence (arguably a good or a bad thing) etc. As mentioned before, they make meaningful methods available, not just "run this servlet". They can support CORBA, JMS and other protocols. I got all that today from the first day of a refresher EJB class.

Many of those requirements show up in high end systems only, and plenty of high capacity sites and apps have been built wihout em for sure.