http://www.onjava.com/lpt/a/1111

It has been a pet peeve of mine that one should not buy into an entire EJB solution just to gain the transparent (container-managed) transactional support for Java objects dealing with relational databases. One could inquire, what is the cost of implementing such a solution in the servlet tier itself? Because transactional support is valuable, whether the solution is distributed or not.

Typically, this transparent transactional support is accomplished by enrolling the active thread with a connection pool manager that the application relies upon for connections. The filtering mechanism is positioned to intercept the calls to an eventual servlet by registering the current thread with a connection pool manager in order to accomplish this. As one can see, the filtering mechanism is ideally suited for interposition, similar in concept to the EJB interposition of remote object calls from the EJB object to the bean instance.