Hibernate 5 – Hello World

The General Steps Needed to Integrate and Configure Hibernate

The following steps are used to create simple hibernate applications:

1. Identify the POJOs that have a database representation.
2. Identify which properties of those POJOs need to be persisted.
3. Annotate each of the POJOs to map your Java object’s properties to columns in a database table.
4. Create the database schema using the schema export tool, use an existing database, or create your own database schema.
5. Add the Hibernate Java libraries to your application’s classpath.
6. Create a Hibernate XML configuration file that points to your database and your mapped classes.
7. In your Java application, create a Hibernate Configuration object that references your XML configuration file.
8. Also in your Java application, build a Hibernate SessionFactory object from the Configuration object.
9. Retrieve the Hibernate Session objects from the SessionFactory, and write your data access logic for your application (create, retrieve, update, and delete).

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. Create a Hibernate configuration file – hibernate.cfg.xml
6. Create a Hibernate utility class
7. Create the Main class and Run an Application

Project Directory Structure

The project directory structure for your reference –

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>hibernate-xml-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)

Let’s create a Student persistent class that is mapped to a database “student” 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.

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 +"]";
    }
}

5. Create a Hibernate configuration file – hibernate.cfg.xml

   The configuration file contains information about the database and mapping file. Conventionally, its name should be hibernate.cfg.xml.

   Let’s create an XML file named as hibernate.cfg.xml under resources folder and write the following code in it.

   < !DOCTYPEhibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
   < hibernate-configuration>
   < session-factory>
   < !-- JDBC Database connection settings -->
   < propertyname="connection.driver_class">com.mysql.cj.jdbc.Driver< /property>
   < propertyname="connection.url">jdbc:mysql://localhost:3306/hibernate_db?useSSL=false</ property>
   < propertyname="connection.username">root< /property>
   < propertyname="connection.password">root< /property>
   < !-- JDBC connection pool settings ... using built-in test pool -->
   < propertyname="connection.pool_size">1< /property>
   < !-- Select our SQL dialect -->
   < propertyname="dialect">org.hibernate.dialect.MySQL5Dialect< /property>
   < !-- Echo the SQL to stdout -->
   < propertyname="show_sql">true< /property>
   < !-- Set the current session context -->
   < propertyname="current_session_context_class">thread< /property>
   < !-- Drop and re-create the database schema on startup -->
   < propertyname="hbm2ddl.auto">create-drop< /property>
   < !--dbcp connection pool configuration -->
   < propertyname="hibernate.dbcp.initialSize">5< /property>
   < propertyname="hibernate.dbcp.maxTotal">20< /property>
   < propertyname="hibernate.dbcp.maxIdle">10< /property>
   < propertyname="hibernate.dbcp.minIdle">5< /property>
   < propertyname="hibernate.dbcp.maxWaitMillis">-1< /property>
   < mappingclass="net.javaguides.hibernate.entity.Student" />
   < /session-factory>
   < /hibernate-configuration>
   

6. Create a Hibernate utility Class

   Create a helper class to bootstrap hibernate SessionFactory. In most Hibernate applications, the SessionFactory should be instantiated once during application initialization. The single instance should then be used by all code in a particular process, and any Session should be created using this single SessionFactory.

   The SessionFactory is thread-safe and can be shared; a Session is a single-threaded object. Let’s create HibernateUtil class to configure singleton SessionFactory and use throughout the application.

   The bootstrapping API is quite flexible, but in most cases, it makes the most sense to think of it as a 3 step process:

1. Build the StandardServiceRegistry
2. Build the Metadata
3. Use those 2 to build the SessionFactory

packagenet.ducatindia.hibernate.util;

importorg.hibernate.SessionFactory;
importorg.hibernate.boot.Metadata;
importorg.hibernate.boot.MetadataSources;
importorg.hibernate.boot.registry.StandardServiceRegistry;
importorg.hibernate.boot.registry.StandardServiceRegistryBuilder;

publicclassHibernateUtil {
privatestaticStandardServiceRegistry registry;
privatestaticSessionFactorysessionFactory;

publicstaticSessionFactorygetSessionFactory() {
if (sessionFactory==null) {
try {
// Create registry
registry=newStandardServiceRegistryBuilder().configure().build();

// Create MetadataSources
MetadataSources sources =newMetadataSources(registry);

// Create Metadata
Metadatametadata=sources.getMetadataBuilder().build();

// Create SessionFactory
sessionFactory=metadata.getSessionFactoryBuilder().build();

            } catch (Exception e) {
e.printStackTrace();
if (registry !=null) {
StandardServiceRegistryBuilder.destroy(registry);
                }
            }
        }
returnsessionFactory;
    }

publicstaticvoidshutdown() {
if (registry !=null) {
StandardServiceRegistryBuilder.destroy(registry);
        }
    }
}

7. Create the main App class and Run an Application

   Here is main App class which is used to connect MySQL database and persist Student object in database table.

   packagenet.ducatindia.hibernate;
   
   importjava.util.List;
   
   importorg.hibernate.Session;
   importorg.hibernate.Transaction;
   
   importnet.javaguides.hibernate.entity.Student;
   importnet.javaguides.hibernate.util.HibernateUtil;
   
   publicclassApp {
   publicstaticvoidmain(String[] args) {
   
   Studentstudent=newStudent("Ramesh", "Fadatare", "rameshfadatare@javaguides.com");
   Student student1 =newStudent("John", "Cena", "john@javaguides.com");
   Transactiontransaction=null;
   try (Sessionsession=HibernateUtil.getSessionFactory().openSession()) {
   // start a transaction
   transaction=session.beginTransaction();
   // save the student objects
   session.save(student);
   session.save(student1);
   // commit transaction
   transaction.commit();
           } catch (Exception e) {
   if (transaction !=null) {
   transaction.rollback();
               }
   e.printStackTrace();
           }
   
   try (Sessionsession=HibernateUtil.getSessionFactory().openSession()) {
   List< Student> students =session.createQuery("from Student", Student.class).list();
   students.forEach(s ->System.out.println(s.getFirstName()));
           } catch (Exception e) {
   if (transaction !=null) {
   transaction.rollback();
               }
   e.printStackTrace();
           }
       }
   }
   
   

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