Hibernate Persist an Entity Example

Author:
In this article, we will create a simple Hibernate 6 application to demonstrate how to persist an entity into a database. We use Session.persist() method to save or persist an entity in the database

Session.persist(Object object) Method

The below diagram shows the snippet of the persisting entity in a database:
Let's start developing step by step Hibernate application using Maven as a project management and build tool. 

Technologies and tools used

  • Hibernate 6.1.7.Final
  • IDE - Eclipse 
  • Maven 3.5.3
  • Java 17
  • MySQL - 8.0.32

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. Maven Dependencies - The pom.xml File

Open your pom.xml file and the below content:
<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-save-entity-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 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 + "]";
    }
}

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

Let's create an XML file named hibernate.cfg.xml under the src/main/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>

6. Create a Hibernate Utility Class

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 main App class which is used to connect MySQL database and persist Student object in a database table. 
Let's test Hibernate application to connect to the MySQL database.
package net.javaguides.hibernate;

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");
        persistStudent(student);
    }

    public static void persistStudent(Student student) {
        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // save the student object
            session.persist(student);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }
}

Output


GitHub Repository

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

Conclusion 

In this article, we have created a step-by-step hibernate application to demonstrate how to persist an entity into a database using Session.persist() method.

You can learn more about Hibernate ORM Framework at Hibernate Tutorial

Comments

Post a Comment

Leave Comment