Wow, this post generated a short burst of heat but not much light! I think the problem is your question conflates dependency injection, XML-based configuration, and the Spring framework. IMHO you have to consider these separately to understand their relative merits.
Dependency injection is simply that if object A requires object B, it can assume that it will be given an instance of object B rather than having to "look up" an instance of object B. This has some very important advantages: - it makes for cleaner code, since you don't have to code the lookup. - it makes your code independent of any particular lookup approach. You can change how your business layer is wired together without changing all of your code. This is particularly important when trying to create libraries to be re-used in different applications. - it makes your code easier to test, since your test code can manually inject stub objects and mocks. So for me, DI is a big win, regardless of how you do it (Spring, Guice, or even code in your app startup that instantiates the objects and wires them together). I don't find the Spring XML configuration to be that much of a problem, since most of the apps I work on have no more than a few dozen object configured there. One thing I like about it, as opposed to some annotation-based approaches, is that it's external to the objects themselves, making the objects more flexible. For example, suppose you had a WidgetDAO that worked with a DataSource. With the Spring XML you could easily create two different WidgetDAO instances each pointing to a different datasource. This would not be so easy with an annotation-based approach. As for the Spring framework itself, I find it contains a whole bunch of functionality that I normally need in a business app, such as declarative transaction management, AOP (e.g. for logging), and sane wrappers around JDBC, JavaMail, and other difficult APIs. If you're not using Spring, you usually have to figure out other ways to do these things. Hope this helps. jk On Wed, Jul 22, 2009 at 06:40:19PM -0700, Dane Laverty wrote: > Due to the fact that nearly every substantial sample Wicket app is > Spring-based, I imagine that there's something awesome about using Spring. > In fact, Wicket is what has finally gotten me to start learning Spring. > > I think I understand the basics of dependency injection -- configure your > objects in xml files and then inject them into your classes -- but I'm still > not clear on the advantage of it. I've read quite a ways into "Spring in > Action", and the author seems to assume that the reader will automatically > see why xml-based dependency injection is great thing. I must just be > missing something here. What I love about Wicket is being free from xml > files. Can anyone give me a concise explanation of how the advantages of > Spring are worth introducing a new layer into my applications? > > Dane --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org For additional commands, e-mail: users-h...@wicket.apache.org
