用户注册时出错
白标错误

This application has no explicit mapping for /error, so you are 
  seeing this as a fallback.
  Wed Oct 24 16:46:26 IST 2018
  There was an unexpected error (type=Bad Request, status=400).
  Failed to convert value of type 'java.lang.String' to required type 
  'int'; nested exception is java.lang.NumberFormatException: For input string: ""

有两种形式的登记和办公
注册（用户）

@Entity
@Table(name="mytable")
public class User {

@Id
private int id;  //Primary key
private String name;
private String mobile;
private String email;
private String college;
private String branch;
private String semester;
private String address;
private String internship;
private String batch;
private String startdate;
private String enddate;
//getters and setters

办公室

@Entity
@Table(name="officeinfo")
public class Office {

@Id
private int sno;
private String batchno;
private int  id;  
private String fees;
private String reciptno;
private String trainer;
//getters and setters

注册中的会话实现，以便填写（office的）id值

@PostMapping("/save-user")
 public String registerUser(@ModelAttribute User user, BindingResult 
 bindingResult, HttpServletRequest request,HttpSession 
 session,@RequestParam("id") int id) {
    userService.saveMyUser(user);
   session.setAttribute("id", id);
    int x = user.getId();
   request.setAttribute("mode", "MODE_HOME");
    return "welcomepage";
}

id的office页面jsp

<div class="form-group">
    <label class="control-label col-md-3">Candidate 
        Registe rNumber</label>
    <div class="col-md-5">
        <input type="text" class="form-control                       
    placeholder="Enter Register Number" 
         name="id" required value="${sessionScope.id }" />
     </div>
    </div>

/项目概念/
一旦用户注册的（值将存储在数据库中），他的id应该自动填写在office窗体页，并保存在数据库中使用会话的概念，但我得到这个错误请帮助！