Friday, September 22, 2017

Simple code to connect to database using hibernate (annotations) and maven

In this paper we will try to write a mavenized java application that will connect to an Oracle database and perform some data manipulation.

First of all, why maven ?
If you have the right jar dependencies whithout maven that's great ! no need to use maven... Personally i've faced a big problem to download and put the correct dependencies (no only packages but versions also!) together into my project.

Then let's talk maven !

1- Create the application with maven


Run this command line :

mvn archetype:generate -DgroupId=com.itillusion.migrators -DartifactId=loader -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false


2- Add dependencies to POM

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<dependency>
    <groupid>org.hibernate</groupid>
    <artifactid>hibernate-core</artifactid>
    <version>5.2.11.Final</version>
</dependency>
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<dependency>
    <groupid>org.hibernate</groupid>
    <artifactid>hibernate-tools</artifactid>
    <version>3.2.0.ga</version>
</dependency>

And that's all, no need to other dependencies ...
So our new pom.xml become :

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<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0" xsi:schemalocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelversion>4.0.0</modelversion>
  <groupid>com.itillusion.migrators</groupid>
  <artifactid>loader</artifactid>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>loader</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupid>junit</groupid>
      <artifactid>junit</artifactid>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
     
    <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
 <dependency>
     <groupid>org.hibernate</groupid>
     <artifactid>hibernate-core</artifactid>
     <version>5.2.11.Final</version>
 </dependency>
 <dependency>
     <groupid>org.hibernate</groupid>
     <artifactid>hibernate-tools</artifactid>
     <version>3.2.0.ga</version>
 </dependency>
      
  </dependencies>
</project>
Note that here we use hibernate 5.2.11

3- Build the HibernateUtils class

This class is recommended, it is a Singleton design pattern implementation, and will facilitate our work

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package com.itillusion.migrators.utils;
 
import java.util.ArrayList;
import java.util.List;
 
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import tn.cnss.referentiel.models.Assure;
import tn.cnss.referentiel.models.Beneficiaire;
 
 
public class HibernateUtils {
 private static final SessionFactory sessionFactory;
 
 
 
 static {
  try {
  StandardServiceRegistry standardRegistry =
  new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
   
  //Annotated  classes to be scanned
  List<class>> classes = new ArrayList<class>>();
  classes.add(Assure.class);
  classes.add(Beneficiaire.class);
   
  //Attach classes
  MetadataSources metadataSources = new MetadataSources(standardRegistry);
  for (Class annotatedClass : classes) {
      metadataSources.addAnnotatedClass(annotatedClass);
  }
 
  sessionFactory = metadataSources.buildMetadata()
      .buildSessionFactory();
 
  } catch (Throwable th) {
 
   System.err.println("Enitial SessionFactory creation failed" + th);
   throw new ExceptionInInitializerError(th);
 
  }
 }
 public static SessionFactory getSessionFactory() {
 
  return sessionFactory;
 
 }
 public static Session getSession() throws org.hibernate.HibernateException {
     SessionFactory sessionFactory = HibernateUtils.getSessionFactory();
     Session sess = null;      
     try {        
         sess = sessionFactory.getCurrentSession(); 
     } catch (org.hibernate.HibernateException he) { 
         sess = sessionFactory.openSession();    
     }            
     return sess;
  }
}
</class></class>
Note in the fragment
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classes.add(Assure.class);
classes.add(Beneficiaire.class);

We have added our annotated classes !
I'm sure that there is a more elegant methods to do this, (iteration on packages using java reflection api) but in my case i just need two tabled to map.

Note also that we conserved our classic hibernate.cfg.xml file. (Surely we can avoid that and use100% java code to confgiure hibernate, but i don't recommand that and it is more logic to store database informations in a separate faile that can change independently from our code)

Here is a simple cfg file:
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<hibernate-configuration>
    <session-factory name="mainSession">
        <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="hibernate.connection.password">PASSWORD</property>
        <property name="hibernate.connection.url">jdbc:oracle:thin:@xxx.yy.zz.tt:SID</property>
        <property name="hibernate.connection.username">USERNAME</property>
        <property name="hibernate.default_schema">DEFAULT_SCHEMA </property><!--USERNAME-->
        <property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>
    </session-factory>
</hibernate-configuration>
to be continued
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