RE: [Springframework-developer] AOP

[<rod...@in...>]

>My question is what is the difference between Spring AOP and 
AspectJ?  What spaces are each trying to fill? etc. 

Quick reply... I'll have to do an AOP FAQ at some point.

1. AspectJ is a language extension. Spring AOP uses dynamic 
proxies, so there's no language extensions and no special 
compilation steps. Spring AOP enables aspects to be used with 
beans in Spring bean factories. Thus use of AOP is hidden 
behind interfaces as an implementation detail. AspectJ is 
much more powerful than any other AOP solution (as it 
introduces new keywords and constructs) but there's a 
learning curve and it's arguably *too* powerful (it's 
possible to do things that might be problematic in large 
projects).

2. JBoss AOP is promising but it's linked to the container. 
To my mind, this is wrong. I don't want EJB to tie me to the 
container without good reason; I also don't want a container-
only AOP solution. Also it means giving up J2EE portability. 
Spring AOP doesn't do anything weird with class loaders, so 
it works in any container. Also, JBoss AOP is more complex to 
use, from what I've seen. It's more powerful in that it 
allows you to intercept field access (as does AspectJ), but 
IMHO this breaks good practice anyway. (Just because we're 
using AOP, we don't want to throw out encapsulation.)

3. The most similar product is probably Jon Tirsen's Nanning 
(SF). Jon and I even worked on an interoperability API, 
enabling the same interceptors to run in each AOP framework, 
but Jon isn't going to implement it in the near future 
(although Spring does already). Nanning is pretty similar in 
what it can do, although it isn't integrated into a bigger 
picture as is Spring AOP.

Spring AOP is about pragmatic use of AOP, right now. 
Declarative transaction management is already available, and 
a good example of what can be done.

Regards,
Rod