почему бы документацию не почитать? ведь это так легко в IDE.. контрол зажал, мышкой тыц по аннотации, и вот, ты уже читаешь:
/**
* A convenience annotation that is itself annotated with
* {@link Controller @Controller} and {@link ResponseBody @ResponseBody}.
* <p>
* Types that carry this annotation are treated as controllers where
* {@link RequestMapping @RequestMapping} methods assume
* {@link ResponseBody @ResponseBody} semantics by default.
*
* <p><b>NOTE:</b> {@code @RestController} is processed if an appropriate
* {@code HandlerMapping}-{@code HandlerAdapter} pair is configured such as the
* {@code RequestMappingHandlerMapping}-{@code RequestMappingHandlerAdapter}
* pair which are the default in the MVC Java config and the MVC namespace.
*
* @author Rossen Stoyanchev
* @author Sam Brannen
* @since 4.0
*/