Implementing JPA ORM in a Java application
We will develop a simple JPA application that can demonstrate the Object relational Mapping of the application.
Step 1: Create the new JPA project using the Intellj Idea named jpa-object-relation-mapping-demo. After creating the project, the file structure looks like the below image.
Step 2: Open the pom.xml and add the below dependencies into the project.
<dependency>
<groupId>org.hibernate.orm</groupId>
<artifactId>hibernate-core</artifactId>
<version>6.0.2.Final</version>
</dependency>
<dependency>
<groupId>org.glassfish.jaxb</groupId>
<artifactId>jaxb-runtime</artifactId>
<version>3.0.2</version>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.28</version>
</dependency>
Step 3: Open the persistence.xml and put the below code into the project and it can configure the database of the project.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<persistence xmlns="https://jakarta.ee/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/persistence https://jakarta.ee/xml/ns/persistence/persistence_3_0.xsd"
version="3.0">
<persistence-unit name="jpa-example">
<properties>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/example"/>
<property name="javax.persistence.jdbc.user" value="root"/>
<property name="javax.persistence.jdbc.password" value=""/>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
</persistence>
Step 4: Create the new Java package named as model. In that package, create the new Entity Java class named as Product.
Go to src > main > java > model > Product and put the below code.
package model;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
@Entity
public class Product {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private double price;
// Getters and Setters
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
}
Step 5: Create the new Java main class named as the MainApplication.
Go to src > main > java > MainApplication and put the below code.
import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;
import model.Product;
public class MainApplication {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpa-example");
EntityManager em = emf.createEntityManager();
// Create
em.getTransaction().begin();
Product product = new Product();
product.setName("Laptop");
product.setPrice(1000.0);
em.persist(product);
em.getTransaction().commit();
// Read
Product retrievedProduct = em.find(Product.class, 1L);
System.out.println(retrievedProduct.getName()); // Output: Laptop
// Update
em.getTransaction().begin();
retrievedProduct.setPrice(1200.0);
em.getTransaction().commit();
// Delete
em.getTransaction().begin();
em.remove(retrievedProduct);
em.getTransaction().commit();
em.close();
emf.close();
}
}
pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.example</groupId>
<artifactId>jpa-object-relation-mapping-demo</artifactId>
<version>1.0-SNAPSHOT</version>
<name>jpa-object-relation-mapping-demo</name>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.target>11</maven.compiler.target>
<maven.compiler.source>11</maven.compiler.source>
<junit.version>5.9.2</junit.version>
</properties>
<dependencies>
<dependency>
<groupId>org.hibernate.orm</groupId>
<artifactId>hibernate-core</artifactId>
<version>6.0.2.Final</version>
</dependency>
<dependency>
<groupId>org.glassfish.jaxb</groupId>
<artifactId>jaxb-runtime</artifactId>
<version>3.0.2</version>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.28</version>
</dependency>
</dependencies>
<build>
<plugins>
</plugins>
</build>
</project>
Step 6: Once the project is completed, run the application. It will then show the Product name as output. Refer the below output image for the better understanding of the concept.
In the above example, we can demonstrate the object relational mapping of the JPA application.
JPA – Object Relational Mapping
JPA in Java is defined as the Java Persistence API and consists of Java specification for accessing, persisting, and maintaining data between Java objects and related databases One of the main features of JPA is Object Relational Mapping (ORM). This is the bridge between, or we can say the difference between an object-oriented domain model and a relational database model.