Where to put @Transactional? In interface specification or implementation?
What is considered the best practice in placing the @Transactional annotation? Should I annotate the interface method or the implementation?
Answer
It really all depends on your application architecture, in my opinion. It depends on how you are proxying your classes. If you have your app set to proxy-target-class='true' (in your application context, then your @Transactional information wont be picked up if you annotate the Interface.
Check out The Spring Docs -- "Tips" for more information.
Spring recommends that you only annotate concrete classes (and methods of concrete classes) with the @Transactional annotation, as opposed to annotating interfaces. You certainly can place the @Transactional annotation on an interface (or an interface method), but this works only as you would expect it to if you are using interface-based proxies. The fact that Java annotations are not inherited from interfaces means that if you are using class-based proxies (proxy-target-class="true") or the weaving-based aspect (mode="aspectj"), then the transaction settings are not recognized by the proxying and weaving infrastructure, and the object will not be wrapped in a transactional proxy, which would be decidedly bad.