I have got importnat questions to decide how to design my web application.

One of then is that I need clear arguments what are the advantages or disadvantages of using EJB over simple JDBC wrapper.
I mean wrapper is like a tool that has a highest class that stands over table in database. You call it O-R table-per-class-hierarchy.
I like this method and i have used it with no problems with a specific web application, but as far as i read about EJB i think more about caching.

For example I have a class Customer with methods
load();
create();
save();
delete();
get__();
set__()
Customer has an encapsulated instance of class TCustomer, that represents the table "customer" in database. Actually TCustomer is a couple of vectors with column values, and TCustomer provides methods to select, update insert and delete of each row. Note, that only those rows of table "customer" are stored in TCustomer members, that are really needed by Customer object. That means table could be opened only with some filter clause "Where ".

So the picture is like this

Database Table or View <==JDBC===> Table---->TCustomer--->Customer

I think it is clear what jdbc wrapper am i using.

I want to know why EJB is better if it really is.

EJB (assuming SLSBs) allow CMT and remoting interface. Transaction librarys such as Spring give you most of the benenfits without the overhead of the container. There are quite a few examples using just a serlet container so check them out. Unless you need clustering and all the stuff then you don't need EJB.

Note that even if you do need clustering you probably don't need EJB. However, if you need a clustered cache - for example the new Hibernate 2.1 support for clustered caches, you do at least need JTA, which probably implies session beans.

After all, EJB CMT just delegates to the JTA subsystem of the respective J2EE container. So even if you need to work with JTA for whatever reason, you should be able to use programmatic demarcation via plain JTA - or preferably the Spring Framework's transaction management with JtaTransactionManager as strategy, for more convenient demarcation means and more reusable business object implementations.

Juergen
(Spring Framework developer)