How can I write only long number as String on form input?

I am making a registration in Spring Boot using Spring Data JPA. I'm facing a problem in placing long values in a form field.

Model class: I have used @NotBlank annotation before private long nsuID, but when the form redirects the nsuID field has filled up by 0.

@Entity
@Table(name="alumnies",uniqueConstraints = @UniqueConstraint(columnNames = "email") )
public class Alumni {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
@Column(name="NSU_ID")
@NotBlank
private long nsuID;
public long getNsuID() {
return nsuID;
}
public void setNsuID(long nsuID) {
this.nsuID = nsuID;
}
}

HTML file:

<div class="form-group"
th:classappend="${#fields.hasErrors('nsuID')}? 'has-error':''">
<label for="nsuID" class="control-label">NSU ID</label> <input
id="nsuID" class="form-control" th:field="*{nsuID}" />
<p class="error-message"
th:each="error : ${#fields.errors('nsuID')}"
th:text="${error}">Validation error</p>
</div>

Controller class:

@Controller
public class RegistraionController {
@Autowired
private UserService us;
@GetMapping("/")
public String showRegistration(Model model) {
Alumni alumni = new Alumni();
model.addAttribute("alumni", alumni);
return "registration";
}
@PostMapping("/registration")
public String saveAlumni(@ModelAttribute("alumni") @Validated Alumni alumni, BindingResult bindingResult) {
Alumni existing = us.findByEmail(alumni.getEmail());
if (existing != null) {
bindingResult.rejectValue("email", null, "There is already an account registered with that email");
}
if (bindingResult.hasErrors()) {
return "registration";
}
us.saveAlumni(alumni);
return "redirect:/";
}
}

As @Dip Halani said, long type variable can't hold null value since it's primitive type variable and long type variable's default value is 0.

And your @NotBlank constraint on nsuID is wrong because it checks that a character sequence's trimmed length is not empty it's usually used for validate given string value must be not null and the trimmed length must be greater than zero.

If you want to validate for non-null value then use @NotNull and replace long nsuID to Long nsuID.

See Difference Between @NotNull, @NotEmpty, and @NotBlank Constraints in Bean Validation

long can not hold null values so it might be converting to 0. try changing it to Long (wrapper class).

@NotBlank 
private Long nsuID;