I've been consulting with a company who have successfully developed a J2EE (EJB+JSP) project using the existing database and working alongside their existing fat client systems.
We're now considering how to migrate the existing systems (Powerbuilder/Sybase with stored procedures) to the new architecture. This needs to be gradual and implies clients based on a mix of Powerbuilder and JSP driven screens.
Has anyone had experience of this sort of migration and do they have any useful tips or warnings of pitfalls they could offer?
One of the problems I have had with such projects in the past (and includes migrating VB/SQLServer to ASP/COM+/SQLServer as well) is user expectation. A GUI client provides much more flexibility in terms of the type of interaction that can be used and user's expectations will need to be managed accordingly. Often I have found that things that are integral to your client app cannot be easily achieved in JSP, but by thinking a little upfront about the best ways to create the new interface, new strategies or techniques of user interaction can be discovered.
Maybe that's just me. Code is easy, people are hard.
1 of the ways I have dealt with this kind of migration (from VB + SQL Server Stored Proc) to J2EE was to vut it up into manageable portion front to back. Started by converting the UI to JSP and have 1 generic JavaBean that calls the stored procedures. In this way, most of the effort was spend getting users to the new Browser based UI while not rengineering the business logic (in the stored proc) too much.
In the later phases, the stored procedures were analysed and redesigned into javabeans or EJBs.