JPA CRUD Example

In this article, we will discuss how to use Java Persistence API to perform CRUD operations against the database. In this example, we are using the MySQL database.
Learn complete JPA at JPA Tutorial - Java Persistence API
Learn Hibernate ORM Framework at Hibernate Tutorial

What are CRUD operations in JPA?

The CRUD stands for Create, Retrieve (Read), Update, and Delete operations on an Entity. 
In JPA the EntityManager is an interface that is associated with a persistence context. It is used to interact with the persistence context. Here are a few important methods of EntityManager, em, which are used to perform the CRUD operations.
  • persist(): This method is used to persist a managed Entity.
  • remove(): This method is used to remove an Entity from the persistence context.
  • merge(): This method is used to save the current state of the Entity to the persistence context.
  • find(): This method is used to load an Entity based on its primary key.
I have written a separate article on an EntityManager interface, just check out at JPA EntityManager interface with an example.
The Java Persistence API is a Java specification for managing, persisting, and accessing data between objects and relational databases. Hibernate is an ORM (Object Relational Mapping) tool that implements JPA specifications. In this example, we will use Hibernate as a JPA provider.
In this post, we will show you how to create or configure a simple JPA application with Hibernate.

Technologies and tools used

  • Hibernate 5.3.7.Final
  • JPA 2.2
  • IDE - Eclipse Noen
  • Maven 3.5.3
  • JavaSE 1.8
  • MySQL - 8.0.13
Let's start developing step by step Hibernate application using Maven as project management and build tool.

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. JPA CRUD Operations
  6. Create a JPA configuration file
  7. Create a JPA helper class
  8. 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>jpa-crud-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)

The below diagram shows the Student JPA entity that is mapped to a database students table.

Well, let's 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 + "]";
    }
}
If you are new to the JPA entity then read my article here to know about JPA entity basics.

5. JPA CRUD Operations

Let's use EntityManager interface methods to create a CRUD Operations against a database.
package net.javaguides.hibernate;

import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;

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

/**
 *  JPA CRUD Operations
 * @author Ramesh Fadatare
 *
 */
public class CRUDOperations {
    public void insertEntity() {
        EntityManager entityManager = JPAUtil.getEntityManagerFactory().createEntityManager();
        EntityTransaction entityTransaction = entityManager.getTransaction();
        entityTransaction.begin();
        Student student = new Student("Ramesh", "Fadatare", "rameshfadatare@javaguides.com");
        entityManager.persist(student);
        entityManager.getTransaction().commit();
        entityManager.close();
    }

    public void findEntity() {
        EntityManager entityManager = JPAUtil.getEntityManagerFactory().createEntityManager();
        entityManager.getTransaction().begin();
        Student student = entityManager.find(Student.class, 1);
        System.out.println("student id :: " + student.getId());
        System.out.println("student firstname :: " + student.getFirstName());
        System.out.println("student lastname :: " + student.getLastName());
        System.out.println("student email :: " + student.getEmail());
        entityManager.getTransaction().commit();
        entityManager.close();
    }

    public void updateEntity() {
        EntityManager entityManager = JPAUtil.getEntityManagerFactory().createEntityManager();
        entityManager.getTransaction().begin();

        Student student = entityManager.find(Student.class, 1);
        System.out.println("student id :: " + student.getId());
        System.out.println("student firstname :: " + student.getFirstName());
        System.out.println("student lastname :: " + student.getLastName());
        System.out.println("student email :: " + student.getEmail());

        // The entity object is physically updated in the database when the transaction
        // is committed
        student.setFirstName("Ram");
        student.setLastName("jadhav");
        entityManager.getTransaction().commit();
        entityManager.close();
    }

    public void removeEntity() {
        EntityManager entityManager = JPAUtil.getEntityManagerFactory().createEntityManager();
        entityManager.getTransaction().begin();

        Student student = entityManager.find(Student.class, 1);
        System.out.println("student id :: " + student.getId());
        System.out.println("student firstname :: " + student.getFirstName());
        System.out.println("student lastname :: " + student.getLastName());
        System.out.println("student email :: " + student.getEmail());
        entityManager.remove(student);
        entityManager.getTransaction().commit();
        entityManager.close();
    }
}

6. Create a JPA configuration file

Create an XML file named persistence.xml under the src/main/java/META-INF folder and write the following code in it.
<persistence
    xmlns="http://xmlns.jcp.org/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
 version="2.1">
    <persistence-unit name="PERSISTENCE">
        <description> Hibernate JPA Configuration Example</description>
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <class>net.javaguides.hibernate.entity.Student</class>
        <properties>
            <property name="javax.persistence.jdbc.driver"
    value="com.mysql.cj.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url"
    value="jdbc:mysql://localhost:3306/hibernate_db" />
            <property name="javax.persistence.jdbc.user" value="root" />
            <property name="javax.persistence.jdbc.password"
    value="root" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.hbm2ddl.auto" value="create-drop" />
        </properties>
    </persistence-unit>
</persistence>

7. Create a JPA helper class

Create a helper class to bootstrap a JPA EntityManagerFactory.
package net.javaguides.hibernate.util;

import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class JPAUtil {
    private static final String PERSISTENCE_UNIT_NAME = "PERSISTENCE";
    private static EntityManagerFactory factory;

    public static EntityManagerFactory getEntityManagerFactory() {
        if (factory == null) {
            factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
        }
        return factory;
    }

    public static void shutdown() {
        if (factory != null) {
            factory.close();
        }
    }
}

8. Create a main class and run an application

Here is the main class to persist the student object using the EntityManager#persist method.
MainApp.java
package net.javaguides.hibernate;

public class App {
    public static void main(String[] args) {
        CRUDOperations crudOperations = new CRUDOperations();
        crudOperations.insertEntity();
        crudOperations.findEntity();
        crudOperations.updateEntity();
        crudOperations.removeEntity();
    }
}

Output


Learn complete JPA at JPA Tutorial - Java Persistence API
Learn Hibernate ORM Framework at Hibernate Tutorial

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Comments

  1. if c, u, d have error, not commit. Why not have rollback()? Thank you !!!

    ReplyDelete

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