Hibernate - load() Method Example

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In this article, we will show you how to use Session.load() method to retrieve an entity from the database. In this article, we will create a simple Hibernate application using Java configuration without using hibernate.cfg.xml to demonstrate the usage of Session.load() method.

Apart from using Session.load(), we can retrieve entity using Session.get() and Session.byId() methods. Check out at Hibernate 5 - get(), load() and byId() Method Examples.

Let’s look at different flavors of load() method available in hibernate session interface.

Overloaded load() methods

public Object load(Class theClass, Serializable id) throws HibernateException
public Object load(String entityName, Serializable id) throws HibernateException
public void load(Object object, Serializable id) throws HibernateException
  1. The first method needs the class type which you would like to load along with a unique ID.
  2. The second method asks for entityName directly and a unique ID. Both methods return the populated entity object as a return value which you will cast to the desired type.
  3. The third takes an object as an argument. The object should be of the same class as the object you would like loaded, and it should be empty. Hibernate will populate that object with the object you requested.
The other load() methods available through hibernate session take a lock mode as an argument too. The lock mode specifies whether Hibernate should look into the cache for the object and which database lock level Hibernate should use for the row (or rows) of data that represent this object.

The following snippet demonstrates all flavors of load() methods: Note that the comments are self-descriptive.
package net.javaguides.hibernate;

import org.hibernate.Session;

import net.javaguides.hibernate.entity.Student;
import net.javaguides.hibernate.util.HibernateUtil;

public class App {
    public static void main(String[] args) {

        Integer studentId = 1;
        /************************** Save Entity ***************************/
        Session sessionOne = HibernateUtil.getSessionFactory().openSession();
        sessionOne.beginTransaction();

        // create new student object
        Student student = new Student("Ramesh", "Fadatare", "rameshfadatare@javaguides.com");

        // save student object to database
        sessionOne.save(student);
        sessionOne.getTransaction().commit();

        /*******************************************************************/

        //Let's open a new session to test load() methods
        Session sessionTwo = HibernateUtil.getSessionFactory().openSession();
        sessionTwo.beginTransaction();

        //first load() method example
        Student student1 = (Student) sessionTwo.load(Student.class, studentId);
        System.out.println(student1.getFirstName() + " - " + student1.getLastName());

        //Let's verify the entity name
        System.out.println(sessionTwo.getEntityName(student1));

        sessionTwo.getTransaction().commit();

        /************************************************************************/

        Session sessionThree = HibernateUtil.getSessionFactory().openSession();
        sessionThree.beginTransaction();

        //second load() method example
        Student student2 = (Student) sessionThree.load("net.javaguides.hibernate.entity.Student", studentId);
        System.out.println(student2.getFirstName() + " - " + student2.getLastName());

        sessionThree.getTransaction().commit();

        /************************************************************************/

        Session sessionFour = HibernateUtil.getSessionFactory().openSession();
        sessionFour.beginTransaction();

        //third load() method example
        Student student3 = new Student();
        sessionFour.load(student3, studentId);
        System.out.println(student3.getFirstName() + " - " + student3.getLastName());

        sessionFour.getTransaction().commit();
    }
}
Let's start developing step by step Hibernate application using Maven as project management and build tool. In this article, we will JPA annotations for mapping between the Student Java class and the database table.

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

  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 - Java Configuration
  6. 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. 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-load-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>8.0.13</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 with 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 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 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 - Java Configuration

The HibernateUtil Java configuration file contains information about the database and mapping file.
HibernateUtil is a helper class to bootstrap hibernate SessionFactory.Add the Student entity to MetadataSources for mapping.
package net.javaguides.hibernate.util;

import java.util.Properties;

import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.cfg.Environment;
import org.hibernate.service.ServiceRegistry;

import net.javaguides.hibernate.entity.Student;

public class HibernateUtil {
    private static SessionFactory sessionFactory;
    public static SessionFactory getSessionFactory() {
        if (sessionFactory == null) {
            try {
                Configuration configuration = new Configuration();

                // Hibernate settings equivalent to hibernate.cfg.xml's properties
                Properties settings = new Properties();
                settings.put(Environment.DRIVER, "com.mysql.cj.jdbc.Driver");
                settings.put(Environment.URL, "jdbc:mysql://localhost:3306/hibernate_db?useSSL=false");
                settings.put(Environment.USER, "root");
                settings.put(Environment.PASS, "root");
                settings.put(Environment.DIALECT, "org.hibernate.dialect.MySQL5Dialect");

                settings.put(Environment.SHOW_SQL, "true");

                settings.put(Environment.CURRENT_SESSION_CONTEXT_CLASS, "thread");

                settings.put(Environment.HBM2DDL_AUTO, "create-drop");

                configuration.setProperties(settings);

                configuration.addAnnotatedClass(Student.class);

                ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
                    .applySettings(configuration.getProperties()).build();

                sessionFactory = configuration.buildSessionFactory(serviceRegistry);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return sessionFactory;
    }
}

6. Create the main App class and Run an Application

Let's test Hibernate application to connect MySQL database.
package net.javaguides.hibernate;

import org.hibernate.Session;

import net.javaguides.hibernate.entity.Student;
import net.javaguides.hibernate.util.HibernateUtil;

public class App {
    public static void main(String[] args) {

        Integer studentId = 1;
        /************************** Save Entity ***************************/
        Session sessionOne = HibernateUtil.getSessionFactory().openSession();
        sessionOne.beginTransaction();

        // create new student object
        Student student = new Student("Ramesh", "Fadatare", "rameshfadatare@javaguides.com");

        // save student object to database
        sessionOne.save(student);
        sessionOne.getTransaction().commit();

        /*******************************************************************/

        //Let's open a new session to test load() methods
        Session sessionTwo = HibernateUtil.getSessionFactory().openSession();
        sessionTwo.beginTransaction();

        //first load() method example
        Student student1 = (Student) sessionTwo.load(Student.class, studentId);
        System.out.println(student1.getFirstName() + " - " + student1.getLastName());

        //Let's verify the entity name
        System.out.println(sessionTwo.getEntityName(student1));

        sessionTwo.getTransaction().commit();

        /************************************************************************/

        Session sessionThree = HibernateUtil.getSessionFactory().openSession();
        sessionThree.beginTransaction();

        //second load() method example
        Student student2 = (Student) sessionThree.load("net.javaguides.hibernate.entity.Student", studentId);
        System.out.println(student2.getFirstName() + " - " + student2.getLastName());

        sessionThree.getTransaction().commit();

        /************************************************************************/

        Session sessionFour = HibernateUtil.getSessionFactory().openSession();
        sessionFour.beginTransaction();

        //third load() method example
        Student student3 = new Student();
        sessionFour.load(student3, studentId);
        System.out.println(student3.getFirstName() + " - " + student3.getLastName());

        sessionFour.getTransaction().commit();
    }
}

Output



GitHub Repository

The complete source code of this article is available on my GitHub Repository - https://github.com/RameshMF/Hibernate-ORM-Tutorials

Conclusion

In this article,  we have created a simple Hibernate application using Java configuration without using hibernate.cfg.xml to demonstrate the usage of the Session.load() method.
You can learn more about Hibernate ORM Framework at Hibernate Tutorial

References

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