Hibernate 5 - Persist an Entity Example

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In the previous article, we have discussed Hibernate 5 - Save an Entity Example. In this article, we will create a simple Hibernate application to demonstrate how to persist an entity into a database.

persist(Object object) Method

Make a transient instance persistent. This operation cascades to associated instances if the association is mapped with cascade="persist"

Below diagram shows the snippet of persisting an entity in a database:

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

Technologies and tools used

Hibernate 5.3.7.Final
IDE - Eclipse Noen
Maven 3.5.3
JavaSE 1.8
MySQL - 8.0.13

Development Steps

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

1. Create a Simple Maven Project

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

2. Project Directory Structure

The project directory structure for your reference -

3. Add jar Dependencies to pom.xml

<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>8.0.13</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.3.7.Final</version>
        </dependency>
    </dependencies>
    <build>
        <sourceDirectory>src/main/java</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</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 table.

A simple Persistent class should follow some rules:

A no-arg constructor: It is recommended that you have a default constructor 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 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 depends 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 javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@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

The configuration file contains information about the database and mapping file. Conventionally, its name should be hibernate.cfg.xml.

You can use Hibernate 5 Java Configuration Example instead of a hibernate.cfg.xml file.

Let's create an XML file named as hibernate.cfg.xml under 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>
        <!-- Select our SQL dialect -->
        <property name="dialect">org.hibernate.dialect.MySQL5Dialect</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

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; a Session is a single-threaded object. Let's create HibernateUtil.java class to configure SessionFactory as a singleton and use throughout the application.

The bootstrapping API is quite flexible, but in most cases, it makes the most sense to think of it as a 3 step process:

Build the StandardServiceRegistry
Build the Metadata
Use those 2 to build the SessionFactory

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 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 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 available on my GitHub Repository - https://github.com/RameshMF/Hibernate-ORM-Tutorials

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

References

Hibernate ORM 5.4.0.Final User Guide

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