class java.math.BigInteger cannot be cast to class java.lang.Integer (java.math.BigInteger and java.lang.Integer are in module java.base of load

Question

I am trying to write a handler for a get request in Spring but I am getting this error:

class java.math.BigInteger cannot be cast to class java.lang.String (java.math.BigInteger and java.lang.String are in module java.base of loader 'bootstrap').

please check my controller class

@GetMapping("getListOfStudentsBasedOnTrainerId/{trainerId}")
public ResponseEntity<List<TrainerIdResponse>>  getListOfStudentsBasedOnTrainerId( @PathVariable int trainerId) 
        throws RecordNotFoundException{
    
    List<TrainerIdResponse> trainerIdresp= userService.getListOfStudentsBasedOnTrainerId(trainerId);
    return new ResponseEntity<List<TrainerIdResponse>>(trainerIdresp,new HttpHeaders(), HttpStatus.OK);
    
}

this is user service method

 public List<TrainerIdResponse> getListOfStudentsBasedOnTrainerId(@PathVariable int trainerId) throws RecordNotFoundException{
        
        List<Object> trainerIdResponse=searchRepository.getListOfStudentsBasedOnTrainerId(trainerId);
        Iterator it =trainerIdResponse.iterator();
         List<TrainerIdResponse> trainerIdList  =new ArrayList<>();
         while(it.hasNext()) {
             Object[] row=(Object[])it.next();
             TrainerIdResponse trainerIdResponse1= new TrainerIdResponse();
             trainerIdResponse1.setStudentid(Integer.valueOf((Integer)row[0]).intValue());
             trainerIdResponse1.setStudentname(String.valueOf(row[1]));
             trainerIdResponse1.setStudentImage(String.valueOf(row[2]));
             trainerIdResponse1.setEnrolleddate(String.valueOf(row[3]));
             trainerIdResponse1.setHighereducation(String.valueOf(row[4]));
             trainerIdResponse1.setUniversity(String.valueOf(row[5]));
             trainerIdResponse1.setEmployement(String.valueOf(row[6]));
             trainerIdResponse1.setLocation(String.valueOf(row[7]));
             trainerIdResponse1.setTrainerid(Integer.valueOf((Integer)row[8]).intValue());
             trainerIdList.add(trainerIdResponse1);
             
             
         }
        
        
        return trainerIdList;
        
    }

my search repository class

   @Query(value ="select u.userid as \"studentid\",u.username as \"studentname\",u.Image_url as \"studentImage\",u.addeddate as \"enrolleddate\", u.highestqualification as \"highereducation\",\r\n"
            + "u.college as \"university\",e.employmenttype as \"employement\",e.location,\r\n"
            + "ur.requestedtoid as \"trainerid\" from users u JOIN userexperience e  \r\n"
            + "on u.userid = e.userid  join userrequests ur on u.userid = ur.requestedtoid \r\n"
            + "where u.userid = ur.requestedtoid or u.userid =:trainerId",nativeQuery = true)
    List<Object> getListOfStudentsBasedOnTrainerId(int trainerId);

my response class

import java.util.Date;

public class TrainerIdResponse {

    private int studentid;
    private String studentname;
    private String studentImage;
    private String enrolleddate;
    private String highereducation;
    private String university;
    private String employement;
    private String location;
    private int trainerid;
    
    
    public int getStudentid() {
        return studentid;
    }
    public void setStudentid(int studentid) {
        this.studentid = studentid;
    }
    public String getStudentname() {
        return studentname;
    }
    public void setStudentname(String studentname) {
        this.studentname = studentname;
    }
    public String getStudentImage() {
        return studentImage;
    }
    public void setStudentImage(String studentImage) {
        this.studentImage = studentImage;
    }
    public  String getEnrolleddate() {
        return enrolleddate;
    }
    public void setEnrolleddate(String enrolleddate) {
        this.enrolleddate = enrolleddate;
    }
    public String getHighereducation() {
        return highereducation;
    }
    public void setHighereducation(String highereducation) {
        this.highereducation = highereducation;
    }
    public String getUniversity() {
        return university;
    }
    public void setUniversity(String university) {
        this.university = university;
    }
    public String getEmployement() {
        return employement;
    }
    public void setEmployement(String employement) {
        this.employement = employement;
    }
    public String getLocation() {
        return location;
    }
    public void setLocation(String location) {
        this.location = location;
    }
    public int getTrainerid() {
        return trainerid;
    }
    public void setTrainerid(int trainerid) {
        this.trainerid = trainerid;
    }
    
    
    
}

Answer 1

There's a lot of "noise" in the comments, hence this "response":

1. Q: What is the actual error message?

• Your title:

class java.math.BigInteger cannot be cast to class java.lang.Integer (java.math.BigInteger and java.lang.Integer are in module java.base of load

• Your body:

class java.math.BigInteger cannot be cast to class java.lang.String (java.math.BigInteger and java.lang.String are in module java.base of loader 'bootstrap').

??Which is it????

2. Q: What line of is causing the error?

   • That's an important reason you're being asked for the stack traceback: the traceback will show where in the source code the error is occurring.
   • POSSIBLE GUESSES:

trainerIdResponse1.setStudentid(Integer.valueOf((Integer)row[0]).intValue()); trainerIdResponse1.setTrainerid(Integer.valueOf((Integer)row[8]).intValue());

3. Q: If the guess is correct, what are the data types of row[0] and row[8] in the underlying database? Do they correspond to Java "BigInteger"?

4. You CANNOT cast "BigInteger" to an Integer. It's possible that's your entire problem. You MAY use BigInteger.intValue() .

EXAMPLE: int myInt = myBigInteger.intValue();

5. Finally, if the underlying value in the database indeed corresponds to a Java BigInteger, you CANNOT use "intValue()" to read it. You'll probably need getBigDecimal() .

Please let us know if any of this information helped.

And please "edit" your post with all the requested information.

---

Per the OP

private int studentid; inside database this is bigserial data type and trainerid this is inside db is int8

So this is the necessary code:

BigInteger studentId = row[0].getBigDecimal();
trainerIdResponse1.setStudentid(studentId.intValue());
Long trainerId = row[8].getLong();
trainerIdResponse1.setTrainerid(trainerId.intValue()).

NOTE: both are narrowing conversions - you risk truncating data.