Hibernate Example Tutorial

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In this tutorial, we will show you how to create a step-by-step Hibernate application using Hibernate 6 and Java 17. We will also connect the Hibernate application to a MySQL database.

Overview

We will define a mapping between the Student Java class and a database table using the Hibernate ORM Framework.

Hibernate ORM Mapping

The General Steps Needed to Integrate and Configure Hibernate

  1. Identify the POJOs that have a database representation.
  2. Identify which properties of those POJOs need to be persisted.
  3. Annotate each of the POJOs to map your Java object's properties to columns in a database table.
  4. Create the database schema using the schema export tool, use an existing database, or create your own database schema.
  5. Add the Hibernate Java libraries to your application’s classpath.
  6. Create a Hibernate XML configuration file that points to your database and your mapped classes.
  7. In your Java application, create a Hibernate Configuration object that references your XML configuration file.
  8. Also in your Java application, build a Hibernate SessionFactory object from the Configuration object.
  9. Retrieve the Hibernate Session objects from the SessionFactory, and write your data access logic for your application (create, retrieve, update, and delete).

Technologies and Tools Used

  • Hibernate 6.1.7.Final
  • Maven 3.5.3
  • Java 17 or later
  • MySQL 8.0.32

Let's start developing a Hibernate application step by step using Maven as a project management and build tool.

Development Steps

1. Create a Simple Maven Project

Use the How to Create a Simple Maven Project in Eclipse article to create a simple Maven project in Eclipse IDE.

2. Project Directory Structure

The project directory structure for your reference: Project Structure

3. Add jar Dependencies to pom.xml

Add the required dependencies to the pom.xml file:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.32</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>6.1.7.Final</version>
</dependency>

Here is the complete pom.xml file for your reference:

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>net.javaguides.hibernate</groupId>
        <artifactId>hibernate-tutorial</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <artifactId>hibernate-xml-config-example</artifactId>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>6.1.7.Final</version>
        </dependency>
    </dependencies>
    <build>
        <sourceDirectory>src/main/java</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>17</source>
                    <target>17</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

4. Creating the JPA Entity Class (Persistent Class)

Let's create a Student persistent class that is mapped to a database "student" table. 

A simple, persistent class should follow some rules:

  • A no-arg constructor: It is recommended to have a default constructor with at least package visibility so that Hibernate can create the instance of the Persistent class by newInstance() method.
  • Provide an identifier property: It is better to assign an attribute as an id. This attribute behaves as a primary key in a database.
  • Declare getter and setter methods: Hibernate recognizes the method by getter and setter method names by default.
  • Prefer non-final class: Hibernate uses the concept of proxies, that depend on the persistent class. The application programmer will not be able to use proxies for lazy association fetching.

Create a Student entity class under net.javaguides.hibernate.entity package as follows:

package net.javaguides.hibernate.entity;

import jakarta.persistence.*;

@Entity
@Table(name = "student")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Column(name = "email")
    private String email;

    public Student() {
    }

    public Student(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    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;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", email=" + email + "]";
    }
}

JPA annotations used in the Student entity:

  • @Entity - Specifies that the class is an entity.
  • @Table - Specifies the table in the database with which this entity is mapped.
  • @Column - Specifies the mapping between a basic entity attribute and the database table column.
  • @Id - Specifies the primary key of the entity.
  • @GeneratedValue - Specifies the generation strategies for the values of primary keys.

5. Create a Hibernate Configuration File - hibernate.cfg.xml

Before creating the Hibernate configuration file, ensure you create a hibernate_db database in the MySQL server.

Create an XML file named hibernate.cfg.xml under the resources folder and write the following code:

<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <!-- JDBC Database connection settings -->
        <property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate_db?useSSL=false</property>
        <property name="connection.username">root</property>
        <property name="connection.password">root</property>
        <!-- JDBC connection pool settings ... using built-in test pool -->
        <property name="connection.pool_size">1</property>
        <!-- Echo the SQL to stdout -->
        <property name="show_sql">true</property>
        <!-- Set the current session context -->
        <property name="current_session_context_class">thread</property>
        <!-- Drop and re-create the database schema on startup -->
        <

property name="hbm2ddl.auto">create-drop</property>
        <!-- dbcp connection pool configuration -->
        <property name="hibernate.dbcp.initialSize">5</property>
        <property name="hibernate.dbcp.maxTotal">20</property>
        <property name="hibernate.dbcp.maxIdle">10</property>
        <property name="hibernate.dbcp.minIdle">5</property>
        <property name="hibernate.dbcp.maxWaitMillis">-1</property>
        <mapping class="net.javaguides.hibernate.entity.Student"/>
    </session-factory>
</hibernate-configuration>

In Hibernate 6, we don't have to specify the dialect because Hibernate 6 will automatically configure it based on the database JDBC driver that we add to the classpath.

6. Create a Hibernate Utility Class

Next, let's create a helper class to bootstrap the Hibernate SessionFactory. In most Hibernate applications, the SessionFactory should be instantiated once during application initialization. The single instance should then be used by all code in a particular process, and any Session should be created using this single SessionFactory. The SessionFactory is thread-safe and can be shared.

Create the HibernateUtil class with the following code to configure SessionFactory as a singleton and use it throughout the application:

package net.javaguides.hibernate.util;

import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

public class HibernateUtil {
    private static StandardServiceRegistry registry;
    private static SessionFactory sessionFactory;

    public static SessionFactory getSessionFactory() {
        if (sessionFactory == null) {
            try {
                // Create registry
                registry = new StandardServiceRegistryBuilder().configure().build();

                // Create MetadataSources
                MetadataSources sources = new MetadataSources(registry);

                // Create Metadata
                Metadata metadata = sources.getMetadataBuilder().build();

                // Create SessionFactory
                sessionFactory = metadata.getSessionFactoryBuilder().build();

            } catch (Exception e) {
                e.printStackTrace();
                if (registry != null) {
                    StandardServiceRegistryBuilder.destroy(registry);
                }
            }
        }
        return sessionFactory;
    }

    public static void shutdown() {
        if (registry != null) {
            StandardServiceRegistryBuilder.destroy(registry);
        }
    }
}

7. Create the Main App Class and Run the Application

Here is the main App class used to connect to the MySQL database and persist the Student object in a database table:

package net.javaguides.hibernate;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.Transaction;

import net.javaguides.hibernate.entity.Student;
import net.javaguides.hibernate.util.HibernateUtil;

public class App {
    public static void main(String[] args) {

        Student student = new Student("Ramesh", "Fadatare", "[email protected]");
        Student student1 = new Student("John", "Cena", "[email protected]");
        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // save the student objects
            session.persist(student);
            session.persist(student1);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }

        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            List<Student> students = session.createQuery("from Student", Student.class).list();
            students.forEach(s -> System.out.println(s.getFirstName()));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Note that we are using Session.persist() method to save the Student entity object into the database.

Output

Output

GitHub Repository

The complete source code of this article is available on my GitHub Repository.

Conclusion

In this article, we’ve developed a step-by-step simple Hibernate example application. You can learn more about the Hibernate ORM Framework at the Hibernate Tutorial.

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