create table EMPLOYEE (
 id INT NOT NULL auto_increment,
 first_name VARCHAR(20) default NULL,
 last_name VARCHAR(20) default NULL,
 salary  INT default NULL,
 PRIMARY KEY (id)
);

create table CERTIFICATE (
 id INT NOT NULL auto_increment,
 certificate_name VARCHAR(30) default NULL,
 employee_id INT default NULL,
 PRIMARY KEY (id)
);

import java.util.*;

public class Employee {
 private int id;
 private String firstName; 
 private String lastName; 
 private int salary;
 private Set certificates;

 public Employee() {}
 public Employee(String fname, String lname, int salary) {
  this.firstName = fname;
  this.lastName = lname;
  this.salary = salary;
 }
 public int getId() {
  return id;
 }
 public void setId( int id ) {
  this.id = id;
 }
 public String getFirstName() {
  return firstName;
 }
 public void setFirstName( String first_name ) {
  this.firstName = first_name;
 }
 public String getLastName() {
  return lastName;
 }
 public void setLastName( String last_name ) {
  this.lastName = last_name;
 }
 public int getSalary() {
  return salary;
 }
 public void setSalary( int salary ) {
  this.salary = salary;
 }

 public Set getCertificates() {
  return certificates;
 }
 public void setCertificates( Set certificates ) {
  this.certificates = certificates;
 }
}

public class Certificate {
 private int id;
 private String name; 

 public Certificate() {}
 public Certificate(String name) {
  this.name = name;
 }
 public int getId() {
  return id;
 }
 public void setId( int id ) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName( String name ) {
  this.name = name;
 }
 public boolean equals(Object obj) {
  if (obj == null) return false;
  if (!this.getClass().equals(obj.getClass())) return false;

  Certificate obj2 = (Certificate)obj;
  if((this.id == obj2.getId()) && (this.name.equals(obj2.getName())))
  {
   return true;
  }
  return false;
 }
 public int hashCode() {
  int tmp = 0;
  tmp = ( id + name ).hashCode();
  return tmp;
 }
}

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
 "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 

<hibernate-mapping>
 <class name="Employee" table="EMPLOYEE">
  <meta attribute="class-description">
   This class contains the employee detail. 
  </meta>
  <id name="id" type="int" column="id">
   <generator class="native"/>
  </id>
  <set name="certificates" cascade="all">
   <key column="employee_id"/>
   <one-to-many class="Certificate"/>
  </set>
  <property name="firstName" column="first_name" type="string"/>
  <property name="lastName" column="last_name" type="string"/>
  <property name="salary" column="salary" type="int"/>
 </class>

 <class name="Certificate" table="CERTIFICATE">
  <meta attribute="class-description">
   This class contains the certificate records. 
  </meta>
  <id name="id" type="int" column="id">
   <generator class="native"/>
  </id>
  <property name="name" column="certificate_name" type="string"/>
 </class>

</hibernate-mapping>

import java.util.*;
 
import org.hibernate.HibernateException; 
import org.hibernate.Session; 
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class ManageEmployee {
 private static SessionFactory factory; 
 public static void main(String[] args) {
  try{
   factory = new Configuration().configure().buildSessionFactory();
  }catch (Throwable ex) { 
   System.err.println("Failed to create sessionFactory object." + ex);
   throw new ExceptionInInitializerError(ex); 
  }
  ManageEmployee ME = new ManageEmployee();
  /* Let us have a set of certificates for the first employee */
  HashSet set1 = new HashSet();
  set1.add(new Certificate("MCA"));
  set1.add(new Certificate("MBA"));
  set1.add(new Certificate("PMP"));
  
  /* Add employee records in the database */
  Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);

  /* Another set of certificates for the second employee */
  HashSet set2 = new HashSet();
  set2.add(new Certificate("BCA"));
  set2.add(new Certificate("BA"));

  /* Add another employee record in the database */
  Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);

  /* List down all the employees */
  ME.listEmployees();

  /* Update employee's salary records */
  ME.updateEmployee(empID1, 5000);

  /* Delete an employee from the database */
  ME.deleteEmployee(empID2);

  /* List down all the employees */
  ME.listEmployees();

 }

 /* Method to add an employee record in the database */
 public Integer addEmployee(String fname, String lname, 
           int salary, Set cert){
  Session session = factory.openSession();
  Transaction tx = null;
  Integer employeeID = null;
  try{
   tx = session.beginTransaction();
   Employee employee = new Employee(fname, lname, salary);
   employee.setCertificates(cert);
   employeeID = (Integer) session.save(employee); 
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
  return employeeID;
 }

 /* Method to list all the employees detail */
 public void listEmployees( ){
  Session session = factory.openSession();
  Transaction tx = null;
  try{
   tx = session.beginTransaction();
   List employees = session.createQuery("FROM Employee").list(); 
   for (Iterator iterator1 = 
       employees.iterator(); iterator1.hasNext();){
   Employee employee = (Employee) iterator1.next(); 
   System.out.print("First Name: " + employee.getFirstName()); 
   System.out.print(" Last Name: " + employee.getLastName()); 
   System.out.println(" Salary: " + employee.getSalary());
   Set certificates = employee.getCertificates();
   for (Iterator iterator2 = 
       certificates.iterator(); iterator2.hasNext();){
     Certificate certName = (Certificate) iterator2.next(); 
     System.out.println("Certificate: " + certName.getName()); 
   }
   }
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
 }
 /* Method to update salary for an employee */
 public void updateEmployee(Integer EmployeeID, int salary ){
  Session session = factory.openSession();
  Transaction tx = null;
  try{
   tx = session.beginTransaction();
   Employee employee = 
     (Employee)session.get(Employee.class, EmployeeID); 
   employee.setSalary( salary );
   session.update(employee);
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
 }
 /* Method to delete an employee from the records */
 public void deleteEmployee(Integer EmployeeID){
  Session session = factory.openSession();
  Transaction tx = null;
  try{
   tx = session.beginTransaction();
   Employee employee = 
     (Employee)session.get(Employee.class, EmployeeID); 
   session.delete(employee); 
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
 }
}

$java ManageEmployee

.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........

First Name: Manoj Last Name: Kumar Salary: 4000
Certificate: MBA
Certificate: PMP
Certificate: MCA
First Name: Dilip Last Name: Kumar Salary: 3000
Certificate: BCA
Certificate: BA
First Name: Manoj Last Name: Kumar Salary: 5000
Certificate: MBA
Certificate: PMP
Certificate: MCA

mysql> select * from employee;

+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 1 | Manoj  | Kumar  | 5000 |
+----+------------+-----------+--------+
1 row in set (0.00 sec)

mysql> select * from certificate;

+----+------------------+-------------+
| id | certificate_name | employee_id |
+----+------------------+-------------+
| 1 | MBA    |   1 |
| 2 | PMP    |   1 |
| 3 | MCA    |   1 |
+----+------------------+-------------+
3 rows in set (0.00 sec)

mysql>

public class Certificate implements Comparable <Certificate>{
 private int id;
 private String name; 

 public Certificate() {}
 public Certificate(String name) {
  this.name = name;
 }
 public int getId() {
  return id;
 }
 public void setId( int id ) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName( String name ) {
  this.name = name;
 }
 public int compareTo(Certificate that){
  final int BEFORE = -1;
  final int AFTER = 1;

  if (that == null) {
   return BEFORE;
  }

  Comparable thisCertificate = this.getName();
  Comparable thatCertificate = that.getName();

  if(thisCertificate == null) {
   return AFTER;
  } else if(thatCertificate == null) {
   return BEFORE;
  } else {
   return thisCertificate.compareTo(thatCertificate);
  }
 }
}

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
 "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 

<hibernate-mapping>
 <class name="Employee" table="EMPLOYEE">
  <meta attribute="class-description">
   This class contains the employee detail. 
  </meta>
  <id name="id" type="int" column="id">
   <generator class="native"/>
  </id>
  <set name="certificates" cascade="all" sort="MyClass">
   <key column="employee_id"/>
   <one-to-many class="Certificate"/>
  </set>
  <property name="firstName" column="first_name" type="string"/>
  <property name="lastName" column="last_name" type="string"/>
  <property name="salary" column="salary" type="int"/>
 </class>

 <class name="Certificate" table="CERTIFICATE">
  <meta attribute="class-description">
   This class contains the certificate records. 
  </meta>
  <id name="id" type="int" column="id">
   <generator class="native"/>
  </id>
  <property name="name" column="certificate_name" type="string"/>
 </class>

</hibernate-mapping>

import java.util.Comparator;

public class MyClass implements Comparator<Certificate>{
 public int compare(Certificate o1, Certificate o2) {
  final int BEFORE = -1;
  final int AFTER = 1;

  /* To reverse the sorting order, multiple by -1 */
  if (o2 == null) {
   return BEFORE * -1;
  }

  Comparable thisCertificate = o1.getName();
  Comparable thatCertificate = o2.getName();

  if(thisCertificate == null) {
   return AFTER * 1;
  } else if(thatCertificate == null) {
   return BEFORE * -1;
  } else {
   return thisCertificate.compareTo(thatCertificate) * -1;
  }
 }
}

import java.util.*;
 
import org.hibernate.HibernateException; 
import org.hibernate.Session; 
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class ManageEmployee {
 private static SessionFactory factory; 
 public static void main(String[] args) {
  try{
   factory = new Configuration().configure().buildSessionFactory();
  }catch (Throwable ex) { 
   System.err.println("Failed to create sessionFactory object." + ex);
   throw new ExceptionInInitializerError(ex); 
  }
  ManageEmployee ME = new ManageEmployee();
  /* Let us have a set of certificates for the first employee */
  TreeSet set1 = new TreeSet();
  set1.add(new Certificate("MCA"));
  set1.add(new Certificate("MBA"));
  set1.add(new Certificate("PMP"));
  
  /* Add employee records in the database */
  Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);

  /* Another set of certificates for the second employee */
  TreeSet set2 = new TreeSet();
  set2.add(new Certificate("BCA"));
  set2.add(new Certificate("BA"));

  /* Add another employee record in the database */
  Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);

  /* List down all the employees */
  ME.listEmployees();

  /* Update employee's salary records */
  ME.updateEmployee(empID1, 5000);

  /* Delete an employee from the database */
  ME.deleteEmployee(empID2);

  /* List down all the employees */
  ME.listEmployees();

 }

 /* Method to add an employee record in the database */
 public Integer addEmployee(String fname, String lname, 
          int salary, SortedSet cert){
  Session session = factory.openSession();
  Transaction tx = null;
  Integer employeeID = null;
  try{
   tx = session.beginTransaction();
   Employee employee = new Employee(fname, lname, salary);
   employee.setCertificates(cert);
   employeeID = (Integer) session.save(employee); 
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
  return employeeID;
 }

 /* Method to list all the employees detail */
 public void listEmployees( ){
  Session session = factory.openSession();
  Transaction tx = null;
  try{
   tx = session.beginTransaction();
   List employees = session.createQuery("FROM Employee").list(); 
   for (Iterator iterator1 = 
       employees.iterator(); iterator1.hasNext();){
   Employee employee = (Employee) iterator1.next(); 
   System.out.print("First Name: " + employee.getFirstName()); 
   System.out.print(" Last Name: " + employee.getLastName()); 
   System.out.println(" Salary: " + employee.getSalary());
   SortedSet certificates = employee.getCertificates();
   for (Iterator iterator2 = 
       certificates.iterator(); iterator2.hasNext();){
     Certificate certName = (Certificate) iterator2.next(); 
     System.out.println("Certificate: " + certName.getName()); 
   }
   }
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
 }
 /* Method to update salary for an employee */
 public void updateEmployee(Integer EmployeeID, int salary ){
  Session session = factory.openSession();
  Transaction tx = null;
  try{
   tx = session.beginTransaction();
   Employee employee = 
     (Employee)session.get(Employee.class, EmployeeID); 
   employee.setSalary( salary );
   session.update(employee);
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
 }
 /* Method to delete an employee from the records */
 public void deleteEmployee(Integer EmployeeID){
  Session session = factory.openSession();
  Transaction tx = null;
  try{
   tx = session.beginTransaction();
   Employee employee = 
     (Employee)session.get(Employee.class, EmployeeID); 
   session.delete(employee); 
   tx.commit();
  }catch (HibernateException e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
  }finally {
   session.close(); 
  }
 }
}

$java ManageEmployee

.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........

First Name: Manoj Last Name: Kumar Salary: 4000
Certificate: PMP
Certificate: MCA
Certificate: MBA
First Name: Dilip Last Name: Kumar Salary: 3000
Certificate: BCA
Certificate: BA
First Name: Manoj Last Name: Kumar Salary: 5000
Certificate: PMP
Certificate: MCA
Certificate: MBA

mysql> select * from employee;

+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 1 | Manoj  | Kumar  | 5000 |
+----+------------+-----------+--------+
1 row in set (0.00 sec)

mysql> select * from certificate;

+----+------------------+-------------+
| id | certificate_name | employee_id |
+----+------------------+-------------+
| 1 | MBA    |   1 |
| 2 | PMP    |   1 |
| 3 | MCA    |   1 |
+----+------------------+-------------+
3 rows in set (0.00 sec)