@Target(value=PARAMETER) @Retention(value=RUNTIME) @Documented public @interface SessionAttribute
The main motivation is to provide convenient access to existing, permanent session attributes (e.g. user authentication object) with an optional/required check and a cast to the target method parameter type.
For use cases that require adding or removing session attributes consider
 injecting org.springframework.web.context.request.WebRequest or
 javax.servlet.http.HttpSession into the controller method.
 
For temporary storage of model attributes in the session as part of the
 workflow for a controller, consider using SessionAttributes instead.
RequestMapping, 
SessionAttributes, 
RequestAttributepublic abstract boolean required
Defaults to true, leading to an exception being thrown
 if the attribute is missing in the session or there is no session.
 Switch this to false if you prefer a null or Java 8
 java.util.Optional if the attribute doesn't exist.