How to create a session variable in Spring MVC 3

1. request.getSession().setAttribute("sessionvar", "session value");
2. @SessionAttributes("sessionvar")

How do these methods differ? Which is the appropriate way to create a session variable?

Both

 request.getSession().setAttribute("sessionvar", "session value");
 @SessionAttributes("sessionvar")

are used to store values in session . But there are differences.

1.) @SessionAttributes annotation

@Controller
@RequestMapping("/editPet.do")
@SessionAttributes("pet")
public class EditPetForm {

// ...

@ModelAttribute("types")
public Collection<PetType> populatePetTypes() {
    return this.clinic.getPetTypes();
}

@RequestMapping(method = RequestMethod.POST)
public String processSubmit(
        @ModelAttribute("pet") Pet pet, BindingResult result, SessionStatus status) {

    new PetValidator().validate(pet, result);
    if (result.hasErrors()) {
        return "petForm";
    }
    else {
        this.clinic.storePet(pet);
        status.setComplete();
        return "redirect:owner.do?ownerId=" + pet.getOwner().getId();
        }
    }
}

The type-level @SessionAttributes annotation declares session attributes used by a specific handler. This will typically list the names of model attributes which should be transparently stored in the session or some conversational storage, serving as form-backing beans between subsequent requests.Reference

2.)request.getSession().setAttribute("sessionvar", "session value");

request.getSession() returns HttpSession object

then

setAttribute("sessionvar", "session value");

You are manually forcing HttpSession to hold value With a key.