The documentation of Spring MVC sometimes says about "handlers" or "request handlers". For instance, http://docs.spring.io/autorepo/docs/spring/4.0.4.RELEASE/javadoc-api/org/springframework/web/servlet/handler/SimpleUrlHandlerMapping.html says:
Implementation of the HandlerMapping interface to map from URLs to request handler beans
Generally speaking, a Controller is Handler, but a Handler doesn't have to be a Controller.
MessageHandler are all handlers which can work with the
DispatcherServlet. ( (
@)Controller is a handler for executing a web request and returning a view.)
Shortly, Handler is just a term it isn't a class nor interface. And it is responsable of executing the Mapping.