Hibernate interceptor

Interceptor

As you've learned, in Hibernate, an object will be created and maintained. O nce an object has been modified, it must be saved to the database. This process continues until the next time the object is needed, it will be loaded from persistent storage.

So an object passes through different stages of its life cycle, and the Interceptor interface provides a way to be called at different stages to perform some of the required tasks. T hese methods are callback functions from the session to the application, allowing the application to examine or manipulate the properties of a persistent object before it is saved, updated, deleted, or uploaded. The following is a list of all the methods available in the Interceptor interface.

Hibernate interceptors give us total control over how objects are applied to applications and databases.

How do I use interceptors?

To create an interceptor, you can implement the Interceptor class directly or inherit the EmptyInterceptor class. Here are some simple steps to use the Hibernate Interceptor feature.

Create an interceptor

We'll inherit EmptyInterceptor in the example, and the interceptor's method will be called automatically when the Employee object is created and updated. You can implement more methods according to your needs.

import java.io.Serializable;
import java.util.Date;
import java.util.Iterator;

import org.hibernate.EmptyInterceptor;
import org.hibernate.Transaction;
import org.hibernate.type.Type;

public class MyInterceptor extends EmptyInterceptor {
   private int updates;
   private int creates;
   private int loads;

   public void onDelete(Object entity,
                     Serializable id,
                     Object[] state,
                     String[] propertyNames,
                     Type[] types) {
       // do nothing
   }

   // This method is called when Employee object gets updated.
   public boolean onFlushDirty(Object entity,
                     Serializable id,
                     Object[] currentState,
                     Object[] previousState,
                     String[] propertyNames,
                     Type[] types) {
       if ( entity instanceof Employee ) {
          System.out.println("Update Operation");
          return true; 
       }
       return false;
   }
   public boolean onLoad(Object entity,
                    Serializable id,
                    Object[] state,
                    String[] propertyNames,
                    Type[] types) {
       // do nothing
       return true;
   }
   // This method is called when Employee object gets created.
   public boolean onSave(Object entity,
                    Serializable id,
                    Object[] state,
                    String[] propertyNames,
                    Type[] types) {
       if ( entity instanceof Employee ) {
          System.out.println("Create Operation");
          return true; 
       }
       return false;
   }
   //called before commit into database
   public void preFlush(Iterator iterator) {
      System.out.println("preFlush");
   }
   //called after committed into database
   public void postFlush(Iterator iterator) {
      System.out.println("postFlush");
   }
}

Create a POJO class

Now let's modify our first example a little bit, and let's use the EMPLOYEE form and the Employee class:

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

   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;
   }
}

Create a database table

The second step is to create a table in your database. A table corresponds to each object that you provide persistence with. Consider that the above objects need to be stored and retrieved into the following RDBM tables:

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 a Mapping profile

This step is to create a mapping file that guides Hibernate on how to map defined classes or classes to database forms.

<?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>
      <property name="firstName" column="first_name" type="string"/>
      <property name="lastName" column="last_name" type="string"/>
      <property name="salary" column="salary" type="int"/>
   </class>
</hibernate-mapping>

Create an Application class

Finally, we'll run the application by creating an application class with main(). It should be noted here that when we create a session object, we use the Interceptor class as an argument.

import java.util.List; 
import java.util.Date;
import java.util.Iterator; 

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();

      /* Add few employee records in database */
      Integer empID1 = ME.addEmployee("Zara", "Ali", 1000);
      Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);
      Integer empID3 = ME.addEmployee("John", "Paul", 10000);

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

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

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

      /* List down new list of the employees */
      ME.listEmployees();
   }
   /* Method to CREATE an employee in the database */
   public Integer addEmployee(String fname, String lname, int salary){
      Session session = factory.openSession( new MyInterceptor() );
      Transaction tx = null;
      Integer employeeID = null;
      try{
         tx = session.beginTransaction();
         Employee employee = new Employee(fname, lname, salary);
         employeeID = (Integer) session.save(employee); 
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }
      return employeeID;
   }
   /* Method to  READ all the employees */
   public void listEmployees( ){
      Session session = factory.openSession( new MyInterceptor() );
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         List employees = session.createQuery("FROM Employee").list(); 
         for (Iterator iterator = 
                           employees.iterator(); iterator.hasNext();){
            Employee employee = (Employee) iterator.next(); 
            System.out.print("First Name: " + employee.getFirstName()); 
            System.out.print("  Last Name: " + employee.getLastName()); 
            System.out.println("  Salary: " + employee.getSalary()); 
         }
         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( new MyInterceptor() );
      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( new MyInterceptor() );
      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(); 
      }
   }
}

Compilation and execution

Here are the steps to compile and run the application mentioned above. Make sure that you have set up PATH and CLASSPATH correctly before processing compilation and execution.

• Create a hibernate profile that is explained .cfg.xml configuration section.
• Create an Employee.hbm map file .xml above.
• Create and compile the Source .java as shown above.
• Create a MyInterceptor file as shown .java source file and compile it.
• Create the ManagementEmployee file as shown .java source file and compile it.
• Execute ManageEmployee to run the program.

You will get the following results, and the records will be created in the EMPLOYEE form.

$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........

Create Operation
preFlush
postFlush
Create Operation
preFlush
postFlush
Create Operation
preFlush
postFlush
First Name: Zara  Last Name: Ali  Salary: 1000
First Name: Daisy  Last Name: Das  Salary: 5000
First Name: John  Last Name: Paul  Salary: 10000
preFlush
postFlush
preFlush
Update Operation
postFlush
preFlush
postFlush
First Name: Zara  Last Name: Ali  Salary: 5000
First Name: John  Last Name: Paul  Salary: 10000
preFlush
postFlush

If you check your EMPLOYEE form, it should have the following results:

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 29 | Zara       | Ali       |   5000 |
| 31 | John       | Paul      |  10000 |
+----+------------+-----------+--------+
2 rows in set (0.00 sec
mysql>