In Hibernate, an object will be created and persisted. Once the object has been changed, it must be saved back to the database. This process continues until the next time the object is needed, and it will be loaded from the persistent store.

Thus, an object passes through different stages in its life cycle and Interceptor Interface provides methods, which can be called at different stages to perform some required tasks. These methods are callbacks from the session to the application, allowing the application to inspect and/or manipulate properties of a persistent object before it is saved, updated, deleted or loaded. Following is the list of all the methods available within the Interceptor interface −

Sr.No.	Method & Description
1	findDirty() This method is be called when the flush() method is called on a Session object.
2	instantiate() This method is called when a persisted class is instantiated.
3	isUnsaved() This method is called when an object is passed to the saveOrUpdate() method/
4	onDelete() This method is called before an object is deleted.
5	onFlushDirty() This method is called when Hibernate detects that an object is dirty (i.e. have been changed) during a flush i.e. update operation.
6	onLoad() This method is called before an object is initialized.
7	onSave() This method is called before an object is saved.
8	postFlush() This method is called after a flush has occurred and an object has been updated in memory.
9	preFlush() This method is called before a flush.

Hibernate Interceptor gives us total control over how an object will look to both the application and the database.

Table of Contents

How to Use Interceptors?

To build an interceptor, you can either implement Interceptor class directly or extend EmptyInterceptor class. Following will be the simple steps to use Hibernate Interceptor functionality.

Create Interceptors

We will extend EmptyInterceptor in our example where Interceptor’s method will be called automatically when Employee object is created and updated. You can implement more methods as per your requirements.
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 POJO Classes

Now, let us modify a little bit our first example where we used EMPLOYEE table and Employee class to play with −

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 Database Tables

Second step would be creating tables in your database. There would be one table corresponding to each object, you are willing to provide persistence. Consider the objects explained above, need to be stored and retrieved into the following RDBMS table −

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 Mapping Configuration File

This step is to create a mapping file that instructs Hibernate — how to map the defined class or classes to the database tables.

<?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 Application Class

Finally, we will create our application class with the main() method to run the application. Here, it should be noted that while creating session object, we used our 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 above-mentioned application. Make sure, you have set PATH and CLASSPATH appropriately before proceeding for the compilation and execution.
• Create hibernate.cfg.xml configuration file as explained in configuration chapter.
• Create Employee.hbm.xml mapping file as shown above.
• Create Employee.java source file as shown above and compile it.
• Create MyInterceptor.java source file as shown above and compile it.
• Create ManageEmployee.java source file as shown above and compile it.
• Execute ManageEmployee binary to run the program.
You would get the following result, and records would be created in the EMPLOYEE table.
$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 table, it should have the following records −
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>

So, this brings us to the end of blog. This Tecklearn ‘Interceptors in Hibernate’ blog helps you with commonly asked questions if you are looking out for a job in Java Programming. If you wish to learn Hibernate and build a career Java Programming domain, then check out our interactive, Java and JEE Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

Java and JEE Training

Java and JEE Training

About the Course

Java and JEE Certification Training is designed by professionals as per the industrial requirements and demands. This training encompasses comprehensive knowledge on basic and advanced concepts of core Java & J2EE along with popular frameworks like Hibernate, Spring & SOA. In this course, you will gain expertise in concepts like Java Array, Java OOPs, Java Function, Java Loops, Java Collections, Java Thread, Java Servlet, and Web Services using industry use-cases and this will help you to become a certified Java expert.

Why Should you take Java and JEE Training?

• Java developers are in great demand in the job market. With average pay going between $90,000/- to $120,000/- depending on your experience and the employers.
• Used by more than 10 Million developers worldwide to develop applications for 15 Billion devices.
• Java is one of the most popular programming languages in the software world. Rated #1 in TIOBE Popular programming languages index (15th Consecutive Year)

What you will Learn in this Course?

Introduction to Java

• Java Fundamentals
• Introduction to Java Basics
• Features of Java
• Various components of Java language
• Benefits of Java over other programming languages
• Key Benefits of Java

Installation and IDE’s for Java Programming Language

• Installation of Java
• Setting up of Eclipse IDE
• Components of Java Program
• Editors and IDEs used for Java Programming
• Writing a Simple Java Program

Data Handling and Functions

• Data types, Operations, Compilation process, Class files, Loops, Conditions
• Using Loop Constructs
• Arrays- Single Dimensional and Multi-Dimensional
• Functions
• Functions with Arguments

OOPS in Java: Concept of Object Orientation

• Object Oriented Programming in Java
• Implement classes and objects in Java
• Create Class Constructors
• Overload Constructors
• Inheritance
• Inherit Classes and create sub-classes
• Implement abstract classes and methods
• Use static keyword
• Implement Interfaces and use it

Polymorphism, Packages and String Handling

• Concept of Static and Run time Polymorphism
• Function Overloading
• String Handling –String Class
• Java Packages

Exception Handling and Multi-Threading

• Exception handling
• Various Types of Exception Handling
• Introduction to multi-threading in Java
• Extending the thread class
• Synchronizing the thread

File Handling in Java

• Input Output Streams
• Java.io Package
• File Handling in Java

Java Collections

• Wrapper Classes and Inner Classes: Integer, Character, Boolean, Float etc
• Applet Programs: How to write UI programs with Applet, Java.lang, Java.io, Java.util
• Collections: ArrayList, Vector, HashSet, TreeSet, HashMap, HashTable

Java Database Connectivity (JDBC)

• Introduction to SQL: Connect, Insert, Update, Delete, Select
• Introduction to JDBC and Architecture of JDBC
• Insert/Update/Delete/Select Operations using JDBC
• Batch Processing Transaction
• Management: Commit and Rollback

Java Enterprise Edition – Servlets

• Introduction to J2EE
• Client Server architecture
• URL, Port Number, Request, Response
• Need for servlets
• Servlet fundamentals
• Setting up a web project in Eclipse
• Configuring and running the web app with servlets
• GET and POST request in web application with demo
• Servlet lifecycle
• Servlets Continued
• Session tracking and filter
• Forward and include Servlet request dispatchers

Java Server Pages (JSP)

• Fundamentals of Java Server Page
• Writing a code using JSP
• The architecture of JSP
• JSP Continued
• JSP elements: Scriptlets, expressions, declaration
• JSP standard actions
• JSP directives
• Introduction to JavaBeans
• ServletConfig and ServletContext
• Servlet Chaining
• Cookies Management
• Session Management

Hibernate

• Introduction to Hibernate
• Introduction to ORM
• ORM features
• Hibernate as an ORM framework
• Hibernate features
• Setting up a project with Hibernate framework
• Basic APIs needed to do CRUD operations with Hibernate
• Hibernate Architecture

POJO (Plain Old Java Object)

• POJO (Plain Old Java Object)
• Persistent Objects
• Lifecycle of Persistent Object

Spring

• Introduction to Spring
• Spring Fundamentals
• Advanced Spring

Got a question for us? Please mention it in the comments section and we will get back to you.

414