Hibernate 5 XML Configuration Example

In this article, we will show you how to create a Hibernate Application using the hibernate.cfg.xml configuration to connect to the MySQL database. Check out the same Hibernate Application using Java configuration without using hibernate.cfg.xml to connect to MySQL database.

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

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

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 this How to Create a Simple Maven Project in Eclipse article to learn how to create a 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 "student" table.

A simple persistent class should follow these 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 the newInstance() method.
• Provide an identifier property: It is better to assign an attribute as the id. This attribute behaves as a primary key in a database.
• Declare getter and setter methods: Hibernate recognizes the method with 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 the 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.

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>
        <!-- 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 theHibernateUtil class to configure a singleton SessionFactory and use it throughout the application.

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

1. Build the StandardServiceRegistry 
2. Build the Metadata 
3. Use those two 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 the main App class, which is used to connect the MySQL database and persist the Student object in the 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.save(student);
            session.save(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();
        }
    }
}

Output

Further Learning

• Hibernate Reference Documentation
• Hibernate Developer Guide
• Spring Hibernate Tutorials