Some questions on EJBs

Question

hi, i am an intermediate javaee developer but i have some questions on EJBs. sometimes i wonder why do i want to use EJBs in an application. if possible please use some illustrations.
1) What problems do EJBs both session bean and message driven bean solve respectively. like what was the motivation behind creating ejbs.
for ex, someone complained to me once that an app his company wrote took time to load large sets of data, and he asked if he should use EJBs, and i am like, does an EJB load data faster? though i think i said it could help, not because i was sure, but because u know the "Biig EJB", it has to solve it.
2) why do people compare spring and ejbs, and sometimes prefer spring over ejbs.
3) in what situations could an EJB be neccessary/advantageous, and what are the disadvantages if any.
thanks.

Answer 1

java_everywhere wrote:
1) What problems do EJBs both session bean and message driven bean solve respectively. like what was the motivation behind creating ejbs.
for ex, someone complained to me once that an app his company wrote took time to load large sets of data, and he asked if he should use EJBs, and i am like, does an EJB load data faster? though i think i said it could help, not because i was sure, but because u know the "Biig EJB", it has to solve it.It doesn't solve any problems, it is a framework that you can use to make your development (and maintenance) cycle easier IF you use it properly. For example, you get integrated JMS support through message driven beans, no extra work needed there. You get container managed transactions, which made my life a whole lot easier once I got over that phase of thinking the server is responsible for everything (it is not, you are still in the driver seat when it comes to transaction management). As part of that transaction management you get out of the box ORM support through the JPA specification. You can take advantage of the load balancing features of the server for heavy weight applications. etc. etc.
In essence you shouldn't think in terms of what EJB technology gives you; what does the entire JEE platform give you, of which EJB technology is only a component?
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2) why do people compare spring and ejbs, and sometimes prefer spring over ejbs.A real world example: when putting together Ikea furniture you can usually get very far with only using those little tools they give you in the package. However, sometimes you are forced to use a screwdriver, a hammer or a drill. And sometimes you use a screwdriver to keep something in place while using the little Ikea tool to put in a screw. Combining the screwdriver and the Ikea tool usually stems from experience where using only one of them took so much longer and was so much more frustrating to get the things done.
Interesting how real world examples usually translate to software development as well. Why would you limit yourself to using only one tool when combining tools could give you more flexibility and could solve a problem easier because you use the strengths of both to compliment each other?
3) in what situations could an EJB be neccessary/advantageous, and what are the disadvantages if any.All technology exists because there was some need for it. Need rises from requirements, so this question is not answered right here and now - it should be asked on a per project basis. I have this project with these requirements, how could EJB technology help here? How could Spring help? How could Struts 2.0 help? etc. etc.