JPA 2 with Hibernate 5 Bootstrapping Example

JPA 2 with Hibernate 5 Bootstrapping Example

The Java Persistence API (a.k.a. JPA) 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 specification.

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.ducatindia.hibernate< /groupId>
< artifactId>hibernate-tutorial< /artifactId>
< version>0.0.1-SNAPSHOT< /version>
< /parent>
< artifactId>hibernate-jpa-config-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>

Creating the JPA Entity Class(Persistent class)

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.

packagenet.ducatindia.hibernate.entity;

importjavax.persistence.Column;
importjavax.persistence.Entity;
importjavax.persistence.GeneratedValue;
importjavax.persistence.GenerationType;
importjavax.persistence.Id;
importjavax.persistence.Table;

@Entity
@Table(name="student")
publicclassStudent {

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name="id")
privateint id;

@Column(name="first_name")
privateStringfirstName;

@Column(name="last_name")
privateStringlastName;

@Column(name="email")
privateString email;

publicStudent() {

    }

publicStudent(StringfirstName, StringlastName, Stringemail) {
this.firstName=firstName;
this.lastName=lastName;
this.email= email;
    }

publicintgetId() {
return id;
    }

publicvoidsetId(intid) {
this.id = id;
    }

publicStringgetFirstName() {
returnfirstName;
    }

publicvoidsetFirstName(StringfirstName) {
this.firstName=firstName;
    }

publicStringgetLastName() {
returnlastName;
    }

publicvoidsetLastName(StringlastName) {
this.lastName=lastName;
    }

publicStringgetEmail() {
return email;
    }

publicvoidsetEmail(Stringemail) {
this.email= email;
    }

@Override
publicStringtoString() {
return"Student [id="+ id +", firstName="+firstName+", lastName="+lastName+", email="+ email +"]";
    }
}

Create a JPA configuration file

Let’s 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-unitname="PERSISTENCE">
< description> Hibernate JPA Configuration Example< /description>
< provider>org.hibernate.jpa.HibernatePersistenceProvider< /provider>
< class>net.ducatindia.hibernate.entity.Student< /class>
< properties>
< propertyname="javax.persistence.jdbc.driver"
value="com.mysql.cj.jdbc.Driver" />
< propertyname="javax.persistence.jdbc.url"
value="jdbc:mysql://localhost:3306/hibernate_db" />
< propertyname="javax.persistence.jdbc.user"value="root" />
< propertyname="javax.persistence.jdbc.password"
value="root" />
< propertyname="hibernate.show_sql"value="true" />
< propertyname="hibernate.hbm2ddl.auto"value="create-drop" />
< /properties>
< /persistence-unit>
< /persistence>

Create a JPA helper class

Let’s create a helper class to bootstrap a JPA EntityManagerFactory.

packagenet.ducatindia.hibernate.util;

importjavax.persistence.EntityManagerFactory;
importjavax.persistence.Persistence;

publicclassJPAUtil {
privatestaticfinalStringPERSISTENCE_UNIT_NAME="PERSISTENCE";
privatestaticEntityManagerFactory factory;

publicstaticEntityManagerFactorygetEntityManagerFactory() {
if (factory ==null) {
factory=Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
        }
return factory;
    }

publicstaticvoidshutdown() {
if (factory !=null) {
factory.close();
        }
    }
}

Create a main class and run an application

Here is the main class to persist student object using the EntityManager#persist method.

MainApp.java

packagenet.ducatindia.hibernate;

importjavax.persistence.EntityManager;

importnet.ducatindia.hibernate.entity.Student;
importnet.ducatindia.hibernate.util.JPAUtil;

publicclassApp {
publicstaticvoidmain(String[] args) {

EntityManagerentityManager=JPAUtil.getEntityManagerFactory().createEntityManager();
entityManager.getTransaction().begin();

Studentstudent=newStudent("rajan", "sharma", "rajansharma@ducatindia.com");
entityManager.persist(student);
entityManager.getTransaction().commit();
entityManager.close();

JPAUtil.shutdown();
    }

}

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