Problems with mapping a controller - spring

Question

I am completely stuck on mapping a controller to a URL. I have searched quite a bit, but cannot figure out what I'm doing wrong, except from the fact that the mapping is just not happening. The parts included are currently the only ones not working.
Controller Code (Part of a bigger controller file with another controller method with value "/course_users")
#RequestMapping(value = "/new_users", method = RequestMethod.GET)
public String addStudent(
Model model,
Principal principal,
HttpServletRequest requestID, HttpServletRequest requestName)
{
Long courseId = Long.parseLong(requestID.getParameter("id"));
User currentUser = userService.findByEmail(principal.getName());
Course currentCourse = courseService.findCourseById(courseId);
model.addAttribute("user", currentUser);
model.addAttribute("courseId", courseId);
try{
if(!currentUser.getRoles().contains(Role.ADMIN) && !currentUser.getRoles().contains(Role.LECTURER)){
String errorMsg = "Nie masz wystarczających uprawnień, aby dodać kursanta";
model.addAttribute("errorMsg", errorMsg);
return "error";
}
List<User> users = userService.findAll();
model.addAttribute("users", users);
String userName = requestName.getParameter("userName");
User newStudent = userService.findByEmail(userName);
courseService.addStudentToCourse(currentCourse, newStudent);
}
catch (IllegalArgumentException e){
String errorMsg = "Podano nieprawidłowe argumenty podczas tworzenia kursu.";
model.addAttribute("errorMsg", errorMsg);
return "error";
}
return "course_users";
}
HTML file code (the file is called "course_users.html")
<div class="container pb-3">
<form th:action="#{/new_users}">
<div class="form-group">
<label for="userName">Dodawany Student:</label>
<select class="form-control" id="userName" th:name="userName">
<option th:each="student : ${users}" th:value="${student.getEmail()}" th:text="${student.getEmail()}"></option>
</select>
</div>
<div class="pt-3">
<button type="submit" class="btn btn-primary">Dodaj studenta</button>
</div>
</form>
EDIT
Relevant part of UserService (Course Service is annotated the same way)
#Service
public class UserService {
private final UserRepository userRepository;
#Autowired
public UserService(UserRepository userRepository) {
this.userRepository = userRepository;
}
//rest of service code
}
The error is located in the header, and is attempting to call getFirstName() on user, which it doesn't seem to be getting (and why I'm assuming the controller is not getting mapped).
I had an identical problem (and error) with the first method, where I swapped #PathVriable for HttpServletRequest which fixed the problem, sadly no such luck here.
Method call: Attempted to call method getFirstName() on null context object
I feel like this is most likely caused by something very minor that I just keep missing.
EDIT2
I decided to see what happens if I (once again) try
#RequestParam(value = "userName") String userName and #PathVariable("courseId") Long courseId with value = "/new_users/{courseId}"
That went about the same until I swapped
<option th:each="student : ${users}" th:value="${student.getEmail()}" th:text="${student.getEmail()}"></option>
with
<option th:each="student : ${course.getEnrolledStudents()}" th:value="${student.getEmail()}" th:text="${student.getEmail()}"></option>
which showed me an entry in the selection list and gave me an expected error page on clicking the button! (since I was trying to add the same person a second time)
Could be that I'm just mucking something up in HTML syntax, or using/adding the model variable users wrong?

Answer 1

Your controller looks fine can you check you annotated your courseService and userService with #Autowired annotation or not.
#Autowired
private CourseService courseService
Share your error message if it doesn't solve your problem.

Answer 2

I understand that this way you would access the user's values added to model, having always created the corresponding getters and setters of each attribute:
<select class="form-control" id="userName" th:name="userName">
<option th:each="student : ${users}" th:value="${student.email}"
th:text="${student.email}"></option>
</select>

Answer 3

Finally found and answer!
Instead of trying to add a model attribute through model.addAttribute, just add it like this:
#ModelAttribute("users")
public List<User> users() {
return userService.findAll();
}
I still couldn't tell you why the other method didn't work, but at least here's one that works.