Headless Exception - netbeans-8

Question

I would like to ask for a solution to my problem:
HTTP Status 500 - Internal Server Error
type Exception report
message Internal Server Error
description The server encountered an internal error that prevented it from
fulfilling this request.
exception
java.awt.HeadlessException
note The full stack traces of the exception and its root causes are available
in the GlassFish Server Open Source Edition 4.1.1 logs.
GlassFish Server Open Source Edition 4.1.1
There are a few tables in the database, but when I need to get records from the table "Student", it keeps showing this error.
domain file :
package domain;
import java.io.Serializable;
import java.util.Objects;
public class Student implements Serializable {
private String studID;
private String studName;
private int studIC;
private String gender;
private String address;
private int contactNo;
public Student(){}
public Student(String studID){
this.studID = studID;
}
public Student(String studID, String studName, int studIC, String gender, String address, int contactNo){
this.studID = studID;
this.studName = studName;
this.studIC = studIC;
this.gender = gender;
this.address = address;
this.contactNo = contactNo;
}
public String getStudID(){
return studID;
}
public void setStudID(String studID){
this.studID = studID;
}
public String getStudName(){
return studName;
}
public void setStudName(String studName){
this.studName = studName;
}
public int getStudIC(){
return studIC;
}
public void setStudIC(int studIC){
this.studIC = studIC;
}
public String getGender(){
return gender;
}
public void setGender(String gender){
this.gender = gender;
}
public String getAddress(){
return address;
}
public void setAddress(String address){
this.address = address;
}
public int getContactNo(){
return contactNo;
}
public void setContactNo(int contactNo){
this.contactNo = contactNo;
}
}
da file :
package da;
import domain.Student;
import java.sql.*;
import javax.swing.*;
public class StudentDA {
private String host = "jdbc:derby://localhost:1527/hostelDB";
private String user = "nbuser";
private String password = "nbuser";
private String tableName = "Student";
private Connection conn;
private PreparedStatement stmt;
public StudentDA(){
createConnection();
}
public void addRecord(Student student) {
String insertStr = "INSERT INTO " + tableName + " VALUES(?, ?, ?, ?, ?, ?)";
try {
stmt = conn.prepareStatement(insertStr);
stmt.setString(1, student.getStudID());
stmt.setString(2, student.getStudName());
stmt.setInt(3, student.getStudIC());
stmt.setString(4, student.getGender());
stmt.setString(5, student.getAddress());
stmt.setInt(6, student.getContactNo());
stmt.executeUpdate();
} catch (SQLException ex) {
JOptionPane.showMessageDialog(null, ex.getMessage(), "ERROR", JOptionPane.ERROR_MESSAGE);
}
}
public Student getRecord(String studID) {
String queryStr = "SELECT * FROM " + tableName + " WHERE StudentID = ?";
Student student = null;
try {
stmt = conn.prepareStatement(queryStr);
stmt.setString(1, studID);
ResultSet rs = stmt.executeQuery();
if (rs.next()) {
student = new Student(studID, rs.getString("StudentName"), rs.getInt("StudentIC"), rs.getString("Gender"), rs.getString("Address"), rs.getInt("ContactNo"));
}
} catch (SQLException ex) {
JOptionPane.showMessageDialog(null, ex.getMessage(), "ERROR", JOptionPane.ERROR_MESSAGE);
}
return student;
}
private void createConnection() {
try {
Class.forName("org.apache.derby.jdbc.ClientDriver");
conn = DriverManager.getConnection(host, user, password);
} catch (Exception ex) {
JOptionPane.showMessageDialog(null, ex.getMessage(), "ERROR", JOptionPane.ERROR_MESSAGE);
}
}
private void shutDown() {
if (conn != null) {
try {
conn.close();
} catch (SQLException ex) {
JOptionPane.showMessageDialog(null, ex.getMessage(), "ERROR", JOptionPane.ERROR_MESSAGE);
}
}
}
}
servlet :
String studID = request.getParameter("studID");
Student stud = studDA.getRecord(studID);
out.println(stud);