When I look at Java frameworks like Hibernate, JPA, or Spring, I usually have the possibility to make my configuration via an xml-file or put annotations directly in my classes.
I am cosistently asking myself what way should I go.
When I use annotations, I have the class and its configuration together but with an xml I get a bigger picture of my system because I can see all class-configurations.
Annotations also get compiled in some way I guess and it should be quicker than parsing the xml, but on the other hand, if I want to change my configuration I have to recompile it instead of just changing the xml file (which might become even more handy for production environments on customer side).
So, when looking at my points, I tend to go the xml-way. But when looking at forums or tutorials usually annotations are used.
What are your pros and cons?
A good rule of thumb: anything you can see yourself wanting to change without a full redeploy (e.g. tweaking performance parameters) should really go in something “soft-configurable” such as an XML file. Anything which is never realistically going to change – or only in the sort of situation where you’ll be having to change the code anyway – can reasonably be in an annotation.
Ignore any ideas of performance differences between annotations and XML – unless your configuration is absolutely massive the difference will be insignificant.
Concentrate on flexibility and readability.