Spring Framework 3 and session attributes

Question

I have form object that I set to request in GET request handler in my Spring controller. First time user enters to page, a new form object should be made and set to request. If user sends form, then form object is populated from request and now form object has all user givern attributes. Then form is validated and if validation is ok, then form is saved to database. If form is not validated, I want to save form object to session and then redirect to GET request handling page. When request is redirected to GET handler, then it should check if session contains form object.

I have figured out that there is @SessionAttributes("form") annotation in Spring, but for some reason following doesnt work, because at first time, session attribute form is null and it gives error:

org.springframework.web.HttpSessionRequiredException: Session attribute 'form' required - not found in session 

Here is my controller:

@RequestMapping(value="form", method=RequestMethod.GET) public ModelAndView viewForm(@ModelAttribute("form") Form form) {     ModelAndView mav = new ModelAndView("form");           if(form == null) form = new Form();     mav.addObject("form", form);     return mav; }  @RequestMapping(value="form", method=RequestMethod.POST) @Transactional(readOnly = true) public ModelAndView saveForm(@ModelAttribute("form") Form form) {     FormUtils.populate(form, request);     if(form.validate())     {         formDao.save();              }     else      {         return viewForm(form);     }     return null; } 

Answer 1

It throws Exception if controller called first time even though added @SessionAttributes({"form"}) to class. So add following populateForm method will fix this.

@SessionAttributes({"form"}) @Controller public class MyController {     @ModelAttribute("form")    public Form populateForm() {        return new Form(); // populates form for the first time if its null    }     @RequestMapping(value="form", method=RequestMethod.GET)    public ModelAndView viewForm(@ModelAttribute("form") Form form) {        ModelAndView mav = new ModelAndView("form");              if(form == null) form = new Form();        mav.addObject("form", form);        return mav;    }     @RequestMapping(value="form", method=RequestMethod.POST)    @Transactional(readOnly = true)    public ModelAndView saveForm(@ModelAttribute("form") Form form) {       // ..etc etc    } }