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Yatin
The author is graduated in Electronics & Telecommunication. During his studies, he has been involved with a significant number of projects ranging from programming and software engineering to telecommunications analysis. He works as a technical lead in the information technology sector where he is primarily involved with projects based on Java/J2EE technologies platform and novel UI technologies.

Hibernate Example Directory Structure

In this tutorial, I will show you how to setup a Hibernate project with Eclipse.

1. Introduction

Hibernate is an ORM (Object relational mapping) tool for java applications. ORM provides a technique for mapping a data representation from object model to relational data model with an SQL (Structured Query Language) based database schema. Hibernate provides data retrieval facilities, the data query, to reduce development time.
 
 
 

1.1 Hibernate Architecture

There are 4 layers in Hibernate architecture i.e. Java Application Layer, Hibernate Framework Layer, Backhand API Layer and Database Layer. Let’s understand the diagram of hibernate architecture:

Fig. 1: Hibernate Architecture

Fig. 1: Hibernate Architecture

For creating the first Hibernate application, we must know the elements of Hibernate architecture. They are as below:

ElementDescription
SessionFactoryThe SessionFactory is a factory of session and client of Connection Provider. It holds second level cache (optional) of data.
SessionThe session object provides an interface between the application and data stored in the database. It is a short-lived object and wraps the JDBC connection. It is a factory of Transaction, Query, and Criteria and holds a first-level cache (mandatory) of data. The Session interface provides methods to INSERT, UPDATE and DELETE the object.
TransactionThe transaction object specifies the atomic unit of work and is an optional parameter in Hibernate framework.
ConnectionProviderIt is a factory of JDBC connections and abstracts the application from Driver Manager or DataSource. It is an optional parameter in Hibernate framework.
TransactionFactoryIt is a factory of Transaction and is again an optional parameter in Hibernate framework.

1.2 Hibernate Advantages

There are many advantages of using the hibernate framework, for e.g.

  • Hibernate eliminates database dependency from the application. If the application is developed using Hibernate, then it can use any database at any point of time.
  • Hibernate increases productivity which has no bounds with application development strategy. We can use either Top-down start with a domain model or bottom-up with an existing database schema.
  • An application written in Hibernate is easy to maintain because small pieces of code are more under stable. ORM reduces lines of code because it emphasizes on business logic and as far as object-oriented domain models and business logic in the Java-based middle-tier is concerned Hibernate is a most useful tool.

Now, open up the Eclipse IDE and let’s see how we can create a Hibernate application!

2. Hibernate Example Directory Structure

Here, we are going to create a simple example of Hibernate application using Eclipse IDE. For creating the first Hibernate application in Eclipse IDE, we need to follow the below steps:

  • Create the java project.
  • Add jar files for hibernate.
  • Create the Persistent class.
  • Create the mapping file for the Persistent class.
  • Create the Configuration file.
  • Create the class that retrieves or stores the persistent object.
  • Run the application.

2.1 Create a Java project

In Eclipse IDE, go to File -> New -> Java Project. Specify the project details as shown in the below image and click Finish.

Fig. 2: Java Project Creation

Fig. 2: Java Project Creation

Note: You can select the available Java in your system. In our case, we are using JDK 8 (1.8.0_111).

2.2 Add Jar files for Hibernate

Download the required jar files which contain Hibernate from the official Hibernate website and keep them in an easily identifiable location. To add the jar files, Right click on your project -> Properties -> Java Build Path -> Add External Jars. Now select all the jar files as shown in the image given below and click ok.

Fig. 3: Hibernate Jar Files

Fig. 3: Hibernate Jar Files

Notes:

  • In this example, we are connecting the application with MySQL database. So, you must add the MySQL-connector-java-<version>-bin.jar to the project.
  • In Dynamic web projects, there are situations where despite adding the required jars to the build path, there would still be a ClassNotFoundException. To solve this, add all jars again in the projectRoot/lib folder.

2.3 Create the Persistent class

To create the persistent class, Right click on src -> New -> Class. Specify the class with a package name (for e.g. com.jcg.first.hibernate.example) and click Finish.

Fig. 4: Persistent Class

Fig. 4: Persistent Class

Add the following code to it:

Sample Employee.java Code

package com.jcg.first.hibernate.example;

public class Employee {

	private int id;  
	private String firstName, lastName;  

	public int getId() {  
		return id;  
	}

	public void setId(int id) {  
		this.id = id;  
	}

	public String getFirstName() {  
		return firstName;  
	}  

	public void setFirstName(String firstName) {  
		this.firstName = firstName;  
	}

	public String getLastName() {  
		return lastName;  
	}

	public void setLastName(String lastName) {  
		this.lastName = lastName;  
	}  
}

2.4 Create the mapping file for Persistent class

To create the mapping file, Right click on src -> New -> File. Specify the file name (for e.g. employee.hbm.xml) and click Finish. It must be outside the package.

Fig. 5: Mapping File

Fig. 5: Mapping File

Add the following code to it:

Sample Mapping File

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">  
  
 <hibernate-mapping>  
  <class name="com.jcg.first.hibernate.example.Employee" table="employee">  
    <id name="id">  
     <generator class="assigned"></generator>  
    </id>  
            
    <property name="firstName"></property>  
    <property name="lastName"></property>              
  </class>              
 </hibernate-mapping>  

2.5 Create the Hibernate Configuration file

The configuration file contains all the information for the database such as connection_url, driver_class, username, password etc. The hbm2ddl.auto property is used to create the table in the database automatically.

To create the configuration file, Right click on src -> New -> File. Now, specify the configuration file name (for e.g. hibernate.cfg.xml) and click Finish.

Fig. 6: Hibernate Configuration File

Fig. 6: Hibernate Configuration File

Add the following code to it:

Sample Hibernate Configuration File

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration SYSTEM "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
   <session-factory>
   <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
   <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

   <!-- Assume testDb Is The Database Name -->
   <property name="hibernate.connection.url">jdbc:mysql://localhost/testDb</property>
   <property name="hibernate.connection.username">root</property>
   <property name="hibernate.connection.password">admin@123</property>

   <!-- List of XML Mapping Files -->
   <mapping resource="employee.hbm.xml"/>

</session-factory>
</hibernate-configuration>

2.6 Create the Hibernate Configuration file

In this class, we are simply storing the employee object to the database. Add the following code to it:

Sample Hibernate Configuration File

package com.jcg.first.hibernate.example;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class StoreData {

	public static void main(String[] args) {
		// Creating Hibernate Configuration Object 
		Configuration cfgObj = new Configuration();
		// Populating the data of the Configuration File
		cfgObj.configure("hibernate.cfg.xml");		 

		// Creating Session Factory Object  
		SessionFactory factoryObj = cfgObj.buildSessionFactory();  

		// Creating Session Object  
		Session sessionObj = factoryObj.openSession();  

		//Creating Transaction Object  
		Transaction transObj = sessionObj.beginTransaction();  

		Employee empObj = new Employee();  
		empObj.setId(101);  
		empObj.setFirstName("Java");  
		empObj.setLastName("Geek");  
		
		// Persisting The Object  
		sessionObj.persist(empObj); 
		
        // Transaction Is Committed To Database
		transObj.commit();	
		sessionObj.close();  

		System.out.println("Employee Data Successfully Saved In Database!"); 
	}
}

2.7 Run the Application

To run the Hibernate application, Right click on the StoreData class -> Run As -> Java Application.

Fig 7: Run Application

Fig 7: Run Application

3. Conclusion

Simple right? Through this example, we learned about the directory structure for a simple Hibernate application. In case you are confused about where you should create the files, you can review the final project structure.

Fig. 8: Hibernate Application Directory Structure

Fig. 8: Hibernate Application Directory Structure

4. Download the Eclipse Project

Download the project from the below link and play around to learn more.

Download
You can download the full source code of this example here: FirstHibernateProject

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