JPA + Maven example

In this quick tutorial, we discuss how to get started working with JPA + Hibernate + Maven application using Mysql DB.

Project Structure

• Import downloaded project into eclipse. If you are new to maven follow Import maven project into eclipse.
• Imported project structure looks like below screen.

pom.xml (Project Object Model):

• It is an XML file that contains information about the project and configuration details used by Maven to build the project.
• We will define required jars or wars or libraries as dependencies. Below is the pom.xml looks like.
• All the required JPA and Hibernate dependencies will be defined here.

<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>

  <groupId>com.javabydeveloper</groupId>
  <artifactId>JPA-Helloworld</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>JPA-Helloworls</name>
  <url>https://javabydeveloper.com</url>

	<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>8.0.11</version>
		</dependency>
		<!-- Hibernate 5.2.6 Final -->
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-core</artifactId>
			<version>5.4.21.Final</version>
		</dependency>
		<!-- <dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-entitymanager</artifactId>
			<version>5.4.21.Final</version>
		</dependency> -->
		<dependency>
			<groupId>javax.xml.bind</groupId>
			<artifactId>jaxb-api</artifactId>
			<version>2.3.1</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>

Update maven dependencies after project imported :

• Right click on project –> select “maven” –> select “Update Project”. Follow below screen.
• Select “Force Update…” check box –> click “OK”. This will update all dependencies to the project.

Run SQL script that provided in sample application:

• Every download of sample application includes sql file also.
• Copy provided sql script and execute using MySql workbench. Follow below screen.
• Paste sql code in the editor –> select part of script or whole script that you want to execute –> issue command CTRL+SHIFT+ENTER (in windows, CMD+SHIFT+ENTER in Mac).

Persistence.xml :

• Every sample application includes persistence.xml inside META-INF directory.
• JPA uses the persistence.xml file to create the connection and setup the required environment. Provides information which is necessary for making database connections.
  • Persistence units are defined by the persistence.xml configuration file.
  • A persistence unit defines a set of all entity classes that are managed by EntityManager instances in an application.

<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="jbd-pu">
		<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
		<properties>
			<property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver" />
			<property name="javax.persistence.jdbc.url"
				value="jdbc:mysql://localhost:3306/jpa_jbd?useJDBCCompliantTimezoneShift=true&amp;useLegacyDatetimeCode=false&amp;serverTimezone=UTC&amp;useSSL=false" />
			<property name="javax.persistence.jdbc.user" value="root" />
			<property name="javax.persistence.jdbc.password"
				value="password" />
			<property name="hibernate.show_sql" value="true" />

			<property name="hibernate.dialect"
				value="org.hibernate.dialect.MySQLInnoDBDialect" />
		</properties>
	</persistence-unit>
</persistence>

Student Entity:

@Table(name="Student")
@Entity(name = "Stu")
public class Student {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
	@GenericGenerator(name = "native", strategy = "native")
	@Column(name = "ID")
	private Long studentId;

	@Column(name = "FNAME")
	private String firstName;

	@Column(name = "LNAME")
	private String lastName;

	@Column(name = "CONTACT_NO")
	private String contactNo;

	// setters, getters and toString()
	
}

App.java – main class to test the code :

• All the entities are available under “domain” source directory.
• You will find App.java, use that class to run the test.

public class App {

	public static void main(String[] args) {

		EntityManagerFactory emf = null;
		EntityManager entityManager = null;
		EntityTransaction transaction = null;

		try {
			emf = Persistence.createEntityManagerFactory("jbd-pu");
			entityManager = emf.createEntityManager();
			transaction = entityManager.getTransaction();
			transaction.begin();

			Student student = new Student();
			student.setFirstName("John");
			student.setLastName("Bloch");
			student.setContactNo("+1-408-575-1317");

			entityManager.persist(student);

			transaction.commit();

			Query q = entityManager.createQuery("select s from Stu s");

			List<Student> resultList = q.getResultList();
			System.out.println("num of sudents:" + resultList.size());
			for (Student next : resultList) {
				System.out.println("next student: " + next);
			}

		} catch (Exception e) {
			System.out.println(e);
			transaction.rollback();
		} finally {
			entityManager.close();
			emf.close();
		}
	}
}

Source code download.