Hibernate Example Tutorial

Author:
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 see how to connect to Hibernate application to the MySQL database.

In this tutorial, we will define a mapping between the Student Java class and database table using Hibernate ORM Framework:

The General Steps Needed to Integrate and Configure Hibernate

The following steps are used to create simple hibernate applications:
  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 step by step Hibernate application using Maven as a project management and build tool.

Development Steps

  1. Create a Simple Maven Project
  2. Project Directory Structure
  3. Add jar Dependencies to pom.xml
  4. Creating the JPA Entity Class(Persistent class)
  5. Create a Hibernate configuration file - hibernate.cfg.xml
  6. Create a Hibernate utility class
  7. Create the Main class and Run an Application

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 -

3. Add jar Dependencies to pom.xml

Next, let's add the required dependencies to the pom.xml file:
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <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>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <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 that you 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: The 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 that we are using in the Student entity:
@Entity - This annotation specifies that the class is an entity. 
@Table - This annotation specifies the table in the database with which this entity is mapped.
@Column - The @Column annotation is used to specify the mapping between a basic entity attribute and the database table column. 
@Id -  This annotation specifies the primary key of the entity
@GeneratedValue - This annotation specifies the generation strategies for the values of primary keys.

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

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

Let's create an XML file named hibernate.cfg.xml under the resources folder and write the following code in it.
<!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>
The configuration file contains information about the database and mapping file. Conventionally, its name should be hibernate.cfg.xml.

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 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.

Let's create 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);
        }
    }
}

Let's understand the above code:

  1. The registry and sessionFactory variables are declared as private and static, which means they can be accessed from other methods in the class and are shared across all instances of the class.

  2. The getSessionFactory() method is declared as public and static, which means it can be accessed from other classes without creating an instance of the HibernateUtil class.

  3. The method checks if the sessionFactory variable is null. If it is null, it creates a new SessionFactory using Hibernate's Configuration and Metadata APIs.

  4. The StandardServiceRegistryBuilder is used to build a StandardServiceRegistry object, which is used by Hibernate to manage services.

  5. The configure() method is called on the StandardServiceRegistryBuilder to load the hibernate.cfg.xml file and configure Hibernate settings, such as the database driver, URL, username, password, and dialect.

  6. The MetadataSources object is created, which is used to define the sources of metadata that Hibernate will use to create the SessionFactory.

  7. The Metadata object is created by calling getMetadataBuilder() on the MetadataSources object and then calling the build() method.

  8. The SessionFactory is created by calling the build() method on the SessionFactoryBuilder, passing in the Metadata object.

  9. If an exception occurs while creating the sessionFactory, the stack trace is printed to the console, and the StandardServiceRegistry object is destroyed if it was created.

  10. The getSessionFactory() method returns the sessionFactory object.

  11. The shutdown() method is declared as public and static, which means it can be accessed from other classes without creating an instance of the HibernateUtil class.

  12. The method checks if the registry object is not null, and if it is not null, it destroys the registry using the destroy() method of the StandardServiceRegistryBuilder.

7. Create the main App class and Run an Application

Here is the main App class which is used to connect 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", "rameshfadatare@javaguides.com");
        Student student1 = new Student("John", "Cena", "john@javaguides.com");
        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) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }
}
Note that we are using Session.persist() method to save the Student entity object into the database.

Output

GitHub Repository

The complete source code of this article is available on my GitHub Repository - https://github.com/RameshMF/Hibernate-ORM-Tutorials

Conclusion

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

Comments

Post a Comment

Leave Comment