Spring boot + JSP przesyłanie obiektu przez formularz. Błąd konwersji.

Witam,

Robię aplikację na zaliczenie i nie mogę sobie poradzić z przesłaniem obiektu z formularza do kontrolera.

Kontroler:

@RequestMapping("/home/profile")
@Controller
public class ProfileController {
    private static Logger logger = LoggerFactory.getLogger(ProfileController.class);
    private final UsersRepository usersRepository;
    private final InvitationsService invitationsService;

    public ProfileController(UsersRepository usersRepository, InvitationsService invitationsService){
        this.usersRepository = usersRepository;
        this.invitationsService = invitationsService;
    }

    @RequestMapping(value = "/{userId}", method = RequestMethod.GET)
    public ModelAndView profile(@PathVariable("userId") Long userId, Model model) throws Exception {
        Optional<User> oUser = this.usersRepository.findByUserId(userId);

        logger.info("USERID {}", userId);
        logger.info("USER {}", oUser.get().getEmail());

        oUser.orElseThrow(() -> new UserNotExistsException());
        User user = oUser.get();
        User logged = ((CustomUser) SecurityContextHolder.getContext().getAuthentication().getPrincipal()).getUser();

        ModelAndView mv = new ModelAndView("profile");
        mv.addObject("user", user);
        mv.addObject("friends", this.invitationsService.usersAreFriends(user, logged));
        mv.addObject("invitation", new Invitation());

        return mv;
    }

    @RequestMapping(value = "/{userId}", method = RequestMethod.POST)
    public ModelAndView invite(@PathVariable("userId") Long userId,
                         @ModelAttribute("invitation")Invitation invitation,
                         BindingResult result,
                         Model model) throws Exception {
        if (result.hasErrors()) {
            for (ObjectError error: result.getAllErrors()) {
                logger.warn("ERROR {}", error.getDefaultMessage());
            }
        }
        User user = invitation.getFromUser();
        logger.info("FROM USER: "  + user.getUserId());
        this.invitationsService.addNewUser(invitation);

        return profile(userId, model);
    }
}

JSP:

<form:form method="post" modelAttribute="invitation">
   <form:input path="fromUser" type="hidden" name="fromUser" value="${logged}"/>
   <form:input path="toUser" type="hidden" name="toUser" value="${user}"/>
   <form:button id="sendInvitation" type="submit" class="btn btn-primary btn-lg"><spring:message code="profile.addToFriends" /></form:button>
</form:form>

Błąd jaki leci to:

2018-03-14 19:10:14.610  WARN 9256 --- [nio-8080-exec-5] c.u.S.controller.ProfileController       : ERROR Failed to convert property value of type 'java.lang.String' to required type 'com.ujazdowski.SocialPortal.model.tables.User' for property 'fromUser'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Long] for value 'User(userId=2, roles=[Role(userRoleId=1, role=USER)], firstName=Bartosz, secondName=Ujazdowski, [email protected], password=$2a$10$da7l/9VRpIPBm1z0LiONwO7wRXMs55.5QOkdpFVQ3/eqO9FBu4IXu, lastTimeOnline=null, profilePhotoId=null, male=true)'; nested exception is java.lang.NumberFormatException: For input string: "User(userId=2,roles=[Role(userRoleId=1,role=USER)],firstName=Bartosz,secondName=Ujazdowski,[email protected],password=$2a$10$da7l/9VRpIPBm1z0LiONwO7wRXMs55.5QOkdpFVQ3/eqO9FBu4IXu,lastTimeOnline=null,profilePhotoId=null,male=true)"
2018-03-14 19:10:14.611  WARN 9256 --- [nio-8080-exec-5] c.u.S.controller.ProfileController       : ERROR Failed to convert property value of type 'java.lang.String' to required type 'com.ujazdowski.SocialPortal.model.tables.User' for property 'toUser'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Long] for value 'User(userId=4, roles=[Role(userRoleId=1, role=USER)], firstName=Kamil, secondName=Stonoga, [email protected], password=$2a$10$eB26PJHiLWOjS7jf/V2bK.5jJZPMUEVViyjBPirN83c7W6/3Hdq8G, lastTimeOnline=null, profilePhotoId=null, male=true)'; nested exception is java.lang.NumberFormatException: For input string: "User(userId=4,roles=[Role(userRoleId=1,role=USER)],firstName=Kamil,secondName=Stonoga,[email protected],password=$2a$10$eB26PJHiLWOjS7jf/V2bK.5jJZPMUEVViyjBPirN83c7W6/3Hdq8G,lastTimeOnline=null,profilePhotoId=null,male=true)"
2018-03-14 19:10:14.613 ERROR 9256 --- [nio-8080-exec-5] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
	at com.ujazdowski.SocialPortal.controller.ProfileController.invite(ProfileController.java:68) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_162]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_162]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_162]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_162]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-4.3.14.RELEASE.jar:4.3.14.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133) ~[spring-web-4.3.14.RELEASE.jar:4.3.14.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97) 

Z góry dziękuje za pomoc ;)

A skąd mamy wiedzieć, która to linia 68? Wstaw sobie w tej linii więcej kodu typu debug output.

Tak sie nie da zrobić jak próbujesz. Tzn nie da się zbindować magiczne całego obiektu jednym inputem formularza. Formularz trzyma stringi i tyle. Musiałbyś zmapować wszystkie pola tego obiektu.