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Session.load() → This method returns a persistence object of the given class with the given identifier. It will throw an exception ObjectNotFoundException if an entity does not exist in the database. The load() method may return a proxy object instead of a real persistence object.
Session.byId() → This method is used to obtain a persistence object by it a primary identifier.
package net.javaguides.hibernate.dao; import org.hibernate.Session; import org.hibernate.Transaction; import net.javaguides.hibernate.entity.Student; import net.javaguides.hibernate.util.HibernateUtil; public class StudentDao { public void getStudent(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // get Student entity using get() method Student student = session.get(Student.class, id); System.out.println(student.getFirstName()); System.out.println(student.getEmail()); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } public void loadStudent(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // get Student entity using load() method Student student = session.load(Student.class, id); System.out.println(student.getFirstName()); System.out.println(student.getEmail()); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } public void getStudentById(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // Obtain an entity using byId() method Student student = session.byId(Student.class).getReference(id); System.out.println(student.getFirstName()); System.out.println(student.getEmail()); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } public void saveStudent(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(); } } }
Technologies and tools used
- Hibernate 6.1.7.Final
- IDE - Eclipse
- Maven 3.5.3
- Java 17
- MySQL - 8.0.32
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 - Java Configuration
- Create StudentDao Class
- 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
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-get-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>8.0.32</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>6.1.7.Final</version>
</dependency>
</dependencies>
<build>
<sourceDirectory>src/main/java</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>17</source>
<target>17</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
4. Creating the JPA Entity Class(Persistent class)

- 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 the newInstance() method.
- Provide an identifier property: It is better to assign an attribute as an 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, which depends on the persistent class. The application programmer will not be able to use proxies for lazy association fetching.
package net.javaguides.hibernate.entity;
import jakarta.persistence.*;
@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
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 StudentDao Class
package net.javaguides.hibernate.dao; import org.hibernate.Session; import org.hibernate.Transaction; import net.javaguides.hibernate.entity.Student; import net.javaguides.hibernate.util.HibernateUtil; public class StudentDao { public void getStudent(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // get Student entity using get() method Student student = session.get(Student.class, id); System.out.println(student.getFirstName()); System.out.println(student.getEmail()); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } public void loadStudent(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // get Student entity using load() method Student student = session.load(Student.class, id); System.out.println(student.getFirstName()); System.out.println(student.getEmail()); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } public void getStudentById(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // Obtain an entity using byId() method Student student = session.byId(Student.class).getReference(id); System.out.println(student.getFirstName()); System.out.println(student.getEmail()); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } public void saveStudent(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(); } } }
7. Create the main App class and Run an Application
package net.javaguides.hibernate; import net.javaguides.hibernate.dao.StudentDao; import net.javaguides.hibernate.entity.Student; public class App { public static void main(String[] args) { StudentDao studentDao = new StudentDao(); Student student = new Student("Ramesh", "Fadatare", "rameshfadatare@javaguides.com"); Student student1 = new Student("Tom", "Cruise", "tom@javaguides.com"); Student student2 = new Student("Tony", "stark", "tony@javaguides.com"); studentDao.saveStudent(student); studentDao.saveStudent(student1); studentDao.saveStudent(student2); studentDao.getStudent(1); studentDao.loadStudent(2); studentDao.getStudentById(3); } }
Output
GitHub Repository
The complete source code of this article is available on my GitHub Repository.Conclusion
In this article, we have created a step-by-step hibernate application to demonstrate the usage of Session.get(), Session.load() and Session.byId() methods to retrieve an entity from database.You can learn more about Hibernate ORM Framework at Hibernate Tutorial
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