Looking for design patterns to isolate framework layers from each other

Question

I'm wondering if anyone has any experience in "isolating" framework objects from each other (Spring, Hibernate, Struts). I'm beginning to see design "problems" where an object from one framework gets used in another object from a different framework. My fear is we're creating tightly coupled objects.

For instance, I have an application where we have a DynaActionForm with several attributes...one of which is a POJO generated by the Hibernate Tools. This POJO gets used everywhere...the JSP populates data to it, the Struts Action sends it down to a Service Layer, the DAO will persist it...ack!

Now, imagine that someone decides to do a little refactoring on that POJO...so that means the JSP, Action, Service, DAO all needs to be updated...which is kind of painful...There has got to be a better way?!

There's a book called Core J2EE Patterns: Best Practices and Design Strategies (2nd Edition)...is this worth a look? I don't believe it touches on any specific frameworks, but it looks like it might give some insight on how to properly layer the application...

Thanks!

Answer 1

For instance, I have an application where we have a DynaActionForm with several attributes...one of which is a POJO generated by the Hibernate Tools. This POJO gets used everywhere...the JSP populates data to it, the Struts Action sends it down to a Service Layer, the DAO will persist it...ack!

To me, there is nothing wrong with having Domain Objects as a "transveral" layer in a web application (after all, you want their state to go from the database to the UI and I don't see the need to map them into intermediate structures):

Now, imagine that someone decides to do a little refactoring on that POJO...so that means the JSP, Action, Service, DAO all needs to be updated...which is kind of painful...There has got to be a better way?!

Sure, you could read "Beans" from the database at the DAO layer level, map them into "Domain Objects" at the service layer and map the Domain Objects into "Value Objects" for the presentation layer and you would have very low coupling. But then you'll realize that:

1. Adding a column in a database usually means adding some information on the view and vice-versa.
2. Duplication of objects and mappings are extremely painful to do and to maintain.

And you'll forget this idea.

There's a book called Core J2EE Patterns: Best Practices and Design Strategies (2nd Edition)...is this worth a look? I don't believe it touches on any specific frameworks, but it looks like it might give some insight on how to properly layer the application...

This book was a "showcase" of how to implement (over engineered) applications using the whole J2EE stack (with EJB 2.x) and has somehow always been considered as too complicated (too much patterns). On top of that, it is today clearly outdated. So it is interesting but must be taken with a giant grain of salt.

In other words, I wouldn't recommend that book (at least certainly not as state of the art). Instead, have a look at Real World Java EE Patterns - Rethinking Best Practices (see Chapter 3 - Mapping of the Core J2EE patterns into Java EE) and/or the Spring literature if you are not using Java EE.

Answer 2

First, avoid Struts 1. Having to extend a framework class (like DynaActionForm) is one of the reasons this framework is no longer a good choice.

You don't use spring classes in the usual scenarios. Spring is non-invasive - it just wires your objects. You depend on it only if using some interfaces like ApplicationContextAware, or if you are using the hibernate or jdbc extensions. Using these extensions together with hibernate/jdbc completely fine and it is not an undesired coupling.

Update: If you are forced to work with Struts 1 (honestly, try negotiating for Struts 2, Struts 1 is obsolete!), the usual way to go was to create a copy of the Form class, that contained the exact same fields, but did not extend the framework class. There would be a factory method that takes the form class and returns the simple POJO. This is duplication of code, but I've seen it in practice and is not that bad (compared to the use of Struts 1 :) )