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Here’s a complete step-by-step guide for setting up our Student Management Application using Hibernate with H2 (In-Memory Database) from scratch.

🚀 Step-by-Step Guide: Hibernate with H2

We will set up Hibernate with an H2 in-memory database it helps to quickly test and understand Hibernate without needing an external database.

🔹 Step 1: Add Dependencies in pom.xml

Modify your pom.xml to include Hibernate and H2 database dependencies.

<dependencies>
    <!-- Hibernate Core -->
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>6.3.1.Final</version>
    </dependency>

    <!-- H2 Database (In-Memory) -->
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <version>2.1.214</version>
        <scope>runtime</scope>
    </dependency>

    <!-- Hibernate Annotations -->
    <dependency>
        <groupId>org.hibernate.common</groupId>
        <artifactId>hibernate-commons-annotations</artifactId>
        <version>6.0.6.Final</version>
    </dependency>

    <!-- Logging Dependencies -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>2.0.7</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-simple</artifactId>
        <version>2.0.7</version>
    </dependency>
</dependencies>

✅ Why H2?

  • In-memory database → No need for MySQL.
  • Resets on every restart → Perfect for testing.
  • Supports SQL similar to MySQL.

🔹 Step 2: Configure Hibernate (hibernate.cfg.xml)

Modify hibernate.cfg.xml to use H2 instead of MySQL.

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <!-- H2 Database Connection -->
        <property name="hibernate.connection.driver_class">org.h2.Driver</property>
        <property name="hibernate.connection.url">jdbc:h2:mem:testdb</property>
        <property name="hibernate.connection.username">sa</property>
        <property name="hibernate.connection.password"></property>

        <!-- Hibernate Dialect for H2 -->
        <property name="hibernate.dialect">org.hibernate.dialect.H2Dialect</property>

        <!-- Show SQL Queries in Console -->
        <property name="hibernate.show_sql">true</property>

        <!-- Automatically create tables -->
        <property name="hibernate.hbm2ddl.auto">update</property>

        <!-- Entity Mapping -->
        <mapping class="com.example.model.Student"/>
    </session-factory>
</hibernate-configuration>

✅ Key Changes

  • jdbc:h2:mem:testdb → Uses H2 in-memory database.
  • hibernate.dialect → Uses H2Dialect.
  • hibernate.hbm2ddl.auto=update → Automatically creates tables.

🔹 Step 3: Create Student Entity

📌 Student.java (Entity class)

package com.example.model;

import jakarta.persistence.*;

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

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

    private String firstName;
    private String lastName;
    private String email;

    public Student() {}

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

    // Getters and Setters
    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 + "'}";
    }
}

✅ Explanation

  • @Entity → Marks this as a Hibernate entity.
  • @Table(name = "students") → Maps the class to students table.
  • @Id → Primary Key.
  • @GeneratedValue(strategy = GenerationType.IDENTITY) → Auto-increment ID.

🔹 Step 4: Create Hibernate Utility Class

📌 HibernateUtil.java

package com.example.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

    private static final SessionFactory sessionFactory = buildSessionFactory();

    private static SessionFactory buildSessionFactory() {
        try {
            return new Configuration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            System.err.println("SessionFactory creation failed: " + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    public static void shutdown() {
        getSessionFactory().close();
    }
}

✅ Why?

  • Manages Hibernate SessionFactory.
  • Provides a single instance for managing sessions.

🔹 Step 5: Verify Connection

📌 Create Main.java

package com.example;

import com.example.model.Student;
import com.example.util.HibernateUtil;
import org.hibernate.Session;
import org.hibernate.Transaction;

public class Main {
    public static void main(String[] args) {
        // Open Hibernate Session
        Session session = HibernateUtil.getSessionFactory().openSession();

        // Begin Transaction
        Transaction transaction = session.beginTransaction();

        // Create a Student Object
        Student student = new Student("John", "Doe", "john.doe@example.com");

        // Save the Student Object
        session.save(student);

        // Commit Transaction
        transaction.commit();

        // Close Session
        session.close();

        System.out.println("Student saved successfully!");
    }
}

✅ Expected Output

Hibernate: create table students (id integer not null auto_increment, email varchar(255), first_name varchar(255), last_name varchar(255), primary key (id))
Hibernate: insert into students (email, first_name, last_name) values (?, ?, ?)
Student saved successfully!
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