JPA CRUD Example

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

What is CRUD operations in JPA?

The CRUD stands for Create, Retrieve (Read), Update and Delete operations on an Entity. From the Java program, we can perform these operations on your Entity. The EntityManager, em represents a JPA link to the relational database which can be used to perform CRUD operations on the Entity objects.
In JPA the EntityManager is an interface which 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 is used to perform the CRUD operations.
  • persist(Object entity): This method is used to persist a managed Entity.
  • remove(Object entity): This method is used to remove an Entity from the persistence context.
  • merge(T entity): This method is used to save the current state of Entity to the persistence context.
  • find(Class entityClass, Object primaryKey): 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 database. Hibernate is an ORM (Object Relational Mapping) tool which implements JPA specification. In this example, we will use Hibernate as 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 How to Create a Simple Maven Project in Eclipse article to create 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)

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 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 depends 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 + "]";
    }
}
If you are new to 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 CRUD Operation 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 as persistence.xml under 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 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();
 }
}

9. Output


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

Comments

  1. cuong369016 November 2019 at 20:28

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

    ReplyDelete

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