Hibernate Session Tutorial: save, persist, saveOrUpdate, get, load, merge, and delete Example

In this tutorial, we will explore various methods provided by the Hibernate Session interface using a Todo entity. These methods include save, persist, saveOrUpdate, get, load, merge, and delete.

Prerequisites

Before we start, ensure you have the following:

Java Development Kit (JDK) installed
Apache Maven installed
MySQL database installed and running (or any other relational database)
An IDE (such as IntelliJ IDEA, Eclipse, or VS Code) installed

Step 1: Setting Up the Project

1.1 Create a Maven Project

Open your IDE and create a new Maven project.
Configure the pom.xml file with the following 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>

    <groupId>com.example</groupId>
    <artifactId>hibernate-session-example</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- Hibernate and JPA -->
        <dependency>
            <groupId>org.hibernate.orm</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>6.4.0.Final</version>
        </dependency>
        <dependency>
            <groupId>jakarta.persistence</groupId>
            <artifactId>jakarta.persistence-api</artifactId>
            <version>3.1.0</version>
        </dependency>

        <!-- MySQL Connector -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.26</version>
        </dependency>

        <!-- SLF4J for logging -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.32</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.32</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>17</source>
                    <target>17</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

1.2 Configure Hibernate

Create a hibernate.cfg.xml file in the src/main/resources directory with the following content:

<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/your_database_name</property>
        <property name="hibernate.connection.username">your_username</property>
        <property name="hibernate.connection.password">your_password</property>
        <property name="hibernate.hbm2ddl.auto">update</property>
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
    </session-factory>
</hibernate-configuration>

Replace your_database_name, your_username, and your_password with your MySQL database credentials.

Step 2: Creating the Entity Class

Create a Todo class in the com.example.hibernatecrud.model package:

package com.example.hibernatecrud.model;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Todo {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String description;
    private boolean completed;

    // Getters and Setters
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public boolean isCompleted() {
        return completed;
    }

    public void setCompleted(boolean completed) {
        this.completed = completed;
    }
}

Step 3: Creating the Utility Class

Create a HibernateUtil class in the com.example.hibernatecrud.util package:

package com.example.hibernatecrud.util;

import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

    private static final SessionFactory sessionFactory = buildSessionFactory();

    private static SessionFactory buildSessionFactory() {
        try {
            Configuration configuration = new Configuration();
            configuration.configure("hibernate.cfg.xml");
            configuration.addAnnotatedClass(com.example.hibernatecrud.model.Todo.class);
            return configuration.buildSessionFactory(new StandardServiceRegistryBuilder()
                    .applySettings(configuration.getProperties()).build());
        } catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

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

Step 4: Using Hibernate Session Methods

4.1 Save

The save method generates a new identifier and inserts the entity into the database.

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

public class SaveExample {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = session.beginTransaction();

        Todo todo = new Todo();
        todo.setTitle("Learn Hibernate");
        todo.setDescription("Study Hibernate save method");
        todo.setCompleted(false);

        session.save(todo);

        transaction.commit();
        session.close();
    }
}

4.2 Persist

The persist method makes an entity instance managed and persistent.

public class PersistExample {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = session.beginTransaction();

        Todo todo = new Todo();
        todo.setTitle("Learn Hibernate");
        todo.setDescription("Study Hibernate persist method");
        todo.setCompleted(false);

        session.persist(todo);

        transaction.commit();
        session.close();
    }
}

4.3 SaveOrUpdate

The saveOrUpdate method either saves a transient instance or updates an attached instance.

public class SaveOrUpdateExample {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = session.beginTransaction();

        Todo todo = new Todo();
        todo.setId(1L); // Assume this ID exists in the database
        todo.setTitle("Learn Hibernate");
        todo.setDescription("Study Hibernate saveOrUpdate method");
        todo.setCompleted(false);

        session.saveOrUpdate(todo);

        transaction.commit();
        session.close();
    }
}

4.4 Get

The get method retrieves an entity by its identifier.

public class GetExample {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Todo todo = session.get(Todo.class, 1L); // Assume this ID exists in the database

        if (todo != null) {
            System.out.println("Title: " + todo.getTitle());
        } else {
            System.out.println("Todo not found");
        }

        session.close();
    }
}

4.5 Load

The load method retrieves an entity by its identifier, but returns a proxy if the entity is not found.

public class LoadExample {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Todo todo = session.load(Todo.class, 1L); // Assume this ID exists in the database

        System.out.println("Title: " + todo.getTitle());

        session.close();
    }
}

4.6 Merge

The merge method copies the state of the given object onto the persistent object with the same identifier.

public class MergeExample {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = session.beginTransaction();

        Todo detachedTodo = new Todo

();
        detachedTodo.setId(1L); // Assume this ID exists in the database
        detachedTodo.setTitle("Learn Hibernate");
        detachedTodo.setDescription("Study Hibernate merge method");
        detachedTodo.setCompleted(true);

        Todo mergedTodo = (Todo) session.merge(detachedTodo);

        transaction.commit();
        session.close();
    }
}

4.7 Delete

The delete method removes the entity instance from the database.

public class DeleteExample {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = session.beginTransaction();

        Todo todo = session.get(Todo.class, 1L); // Assume this ID exists in the database
        if (todo != null) {
            session.delete(todo);
        }

        transaction.commit();
        session.close();
    }
}

Conclusion

In this tutorial, we explored various methods provided by the Hibernate Session interface using a Todo entity. These methods include save, persist, saveOrUpdate, get, load, merge, and delete. By following these examples, you can effectively manage data persistence in your Java applications using Hibernate.

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