Hibernate Basics & Simple Example

Hibernate is an open source Object Relational Mapping framework used to transform from object oriented programming to relational databases.

It supports object oriented concepts Association, Polymorphism, Inheritance & Composition through persistent classes. Also Hibernate facilitates to write queries in variant forms,  HQL(Hibernate Query Language), Native SQL, or Criteria API.

The following question may raise while learning about Hibernate.

What’s the difference between JDBC & Hibernate?

JDBC API’s are easy to use for small projects. But Hibernate framework is well suited for enterprise level applications and acts as mediator between object & relational approaches.

Hibernate Architecture
Hibernate performs the following operations;

• opens a database connection
• converts HQL statements to database specific statements
• execute it  & receive data from the database
• result set being mapped to equivalent java objects to be processed by application.

Hibernate Architecture

This blog gives you a basic idea about how to connect and use Hibernate with a database.

Simple Application : BookApps

BookApps is an example application. This application main function is to add, update, delete, retrieve books from the database.

Note : This application uses a PostgreSQL database, therefore run an instance of PostgreSQL. Go through this blog, to know the basics of PostgreSQL. Also download and run the same.

Click here to download the hibernate & unzip the file hibernate-distribution-3.6.0.Final-dist.zip

Hibernate configuration file : hibernate.cfg.xml
This will have all the information to connect Hibernate to a database. In this example, PostgreSQL database is used.
Note : Hibernate configurations can also be done through hibernate.properties file.

 <!--<span class="hiddenSpellError" pre=""-->DOCTYPE hibernate-configuration PUBLIC
 "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 <a href="http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"</a>>

 <hibernate-configuration>
 <session-factory>
 <!-- Database connection settings -->
 jdbc:postgresql://localhost:5432/postgres
 <property name="connection.driver_class">org.postgresql.Driver</property>
 <property name="connection.username">postgres</property>
 <property name="connection.password">******</property>
 <property name="transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property>

 <!-- SQL dialect - generate SQL for a particular database -->
 <property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>

 <!-- Echo all executed SQL statements -->
 <property name="show_sql">true</property>

 <!-- Enable Hibernate's automatic session context management -->
 <property name="current_session_context_class">thread</property>
<!-- Mapping resource configuration files -->
 <mapping resource="src/com/bookstore/bookapp.hbm.xml"/>
 </session-factory>
 </hibernate-configuration>
 

Property to drop and re-create the database schema on startup

<property name="hbm2ddl.auto">create</property>

By adding this property, hibernate will create tables for you. This will be executed only once ie) after first run comment this code. because every time tables will get dropped.

Hibernate mapping file : bookapp.hbm.xml
For all objects to be persisted in the database,  Hibernate needs this XML file. The mapping file tells Hibernate how to load and store objects, what table in the database it has to access and what columns in the table should use.
This file should be saved with .hbm.xml file extension.

 <?xml version="1.0"?>
 <!--<span class="hiddenSpellError" pre=""-->DOCTYPE hibernate-mapping PUBLIC
 "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 <a href="http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"</a>>

 <hibernate-mapping package="com.bookstore">
 BookDetails" table="BookStore">
 BookId">
 <generator/>
 </id>
 bookName" type="string" column="BookName"/>
 authorName" type="string" column="AuthorName"/>
 bookCost" type="int" column="BookCost"/>
 </class>
 </hibernate-mapping>
 

Persistent class : BookDetails.java
The persistent class works in the form of POJO(Plain Old Java Object) model. It’s a java bean class having getter and setter methods to access the properties of an app.

 package com.bookstore;

 public class BookDetails{
 private int bookId;
 private String bookName;
 private String authorName;
 private int bookCost;

 BookDetails(){
 }

 public int getBookId(){
 return bookId;
 }
 public void setBookId(int bookId){
 this.bookId = bookId;
 }

 public String getBookName(){
 return bookName;
 }
 public void setBookName(String bookName){
 this.bookName = bookName;
 }

 public String getAuthorName(){
 return authorName;
 }
 public void setAuthorName(String authorName){
 this.authorName = authorName;
 }

 public int getBookCost(){
 return bookCost;
 }
 public void setBookCost(int bookCost){
 this.bookCost = bookCost;
 }

 public String toString(){
 StringBuffer sb = new StringBuffer();
 sb.append("BookName : ").append(bookName);
 sb.append(" ,AuthorName : ").append(authorName);
 sb.append(" , BookCost : ").append(bookCost);
 return sb.toString();
 }
 }
 

Hibernate communication with database : HibernateUtil.java
Load the hibernate configuration file and mapping files automatically, create a session factory from the configured object, create a session to execute the HQL query and get the result set of java objects.

 package com.bookstore;

 import org.hibernate.SessionFactory;
 import org.hibernate.cfg.Configuration;

 public class HibernateUtil {

 private static final SessionFactory sessionFactory;

 static {
 try {
 // Create the SessionFactory from hibernate.cfg.xml
 sessionFactory = new Configuration().configure().buildSessionFactory();
 } catch (Throwable ex) {
 // Make sure you log the exception, as it might be swallowed
 System.err.println("Initial SessionFactory creation failed." + ex);
 throw new ExceptionInInitializerError(ex);
 }
 }

 public static SessionFactory getSessionFactory() {
 return sessionFactory;
 }

 }

Application class : BookApp.java
A simple application class which performs CRUD operations in the database through HQL, Persistent Objects, Native SQL & Criteria API.

package com.bookstore;

 import java.util.List;
 import java.util.Iterator;
 import org.hibernate.Session;
 import org.hibernate.Query;
 import org.hibernate.Criteria;
 import org.hibernate.criterion.Restrictions;
 public class BookApp{
 public static void main(String args[]){
 BookMethods bm = new BookMethods();

 //Adding books
 bm.addBook("Professional Hibernate","Eric Pugh, Gradecki", 350);
 bm.addBook("Hibernate in Action","Christian Bauer, Gavin King", 499);
 bm.addBook("Java Persistence With Hibernate","Bauer, Gavin King", 423);
 bm.addBook("Begining Hibernate","Dave Minter, Jeff Linwood", 1500);

 //Listing added books
 bm.listBooks();

 //Getting book details for a particular book name.
 bm.getBookDetails("Hibernate in Action");

 //To see no. of books
 bm.countBook();

 //Update particular book cost
 bm.updateBook("Begining Hibernate",1000);

 //Listing available books
 bm.listBooks();

 //Deleting a book
 bm.deleteBook("Java Persistence With Hibernate");

 //Listing available books After executing delete
 bm.listBooks();
 }
 }

 class BookMethods{
 //Using persistent objects to store data into the database.
 public void addBook(String bookName, String authorName, int bookCost){
 Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 session.beginTransaction();
 BookDetails bd = new BookDetails();
 bd.setBookName(bookName);
 bd.setAuthorName(authorName);
 bd.setBookCost(bookCost);
 session.save(bd);
 session.getTransaction().commit();
 }

 //Using persistence object to delete a row from the database.
 public void deleteBook(String bookName){
 Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 session.beginTransaction();
 List list = session.createQuery("from BookDetails where bookName='"+bookName+"'").list();
 Iterator itr = list.iterator();
 while(itr.hasNext()){
 BookDetails bd = (BookDetails)itr.next();
 System.out.println("delete : "+bd);
 session.delete(bd);
 }
 session.getTransaction().commit();
 }

 //Using Criteria API to update the book cost
 public void updateBook(String bookName, int bookCost){
 Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 session.beginTransaction();
 Criteria cri = session.createCriteria(BookDetails.class);
 cri = cri.add(Restrictions.eq("bookName", bookName));
 List list = cri.list();
 BookDetails bd = (BookDetails)list.iterator().next();
 bd.setBookCost(bookCost);
 session.update(bd);
 session.getTransaction().commit();
 }

 //Using HQL - Hibernate Query Language
 public void getBookDetails(String bookName){
 Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 session.beginTransaction();
 Query q = session.createQuery("from BookDetails where bookName=:bn");
 q.setString("bn", bookName);
 List list = q.list();
 System.out.println("Getting Book Details using HQL. \n"+list);

 //The above query can also be achieved with Criteria & Restrictions API.
 Criteria cri = session.createCriteria(BookDetails.class);
 cri = cri.add(Restrictions.eq("bookName", bookName));
 list = cri.list();
 System.out.println("Getting Book Details using Criteria API. \n"+list);

 session.getTransaction().commit();
 }

 //Aggregate function.
 public void countBook(){
 Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 session.beginTransaction();
 List list = session.createQuery("select count(*) from BookDetails").list();
 System.out.println("Aggregate function count \n"+list);
 session.getTransaction().commit();
 }

 //Native SQL Query
 public void listBooks(){
 Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 session.beginTransaction();
 List list = session.createSQLQuery("select * from BookStore").addEntity(BookDetails.class).list();
 Iterator itr = list.iterator();
 while(itr.hasNext()){
 BookDetails bd = (BookDetails)itr.next();
 System.out.println(bd);
 }
 session.getTransaction().commit();

 }
 }

Compile & Run the simple application : BookApp.

Setting classpath
Following jars are required to compile and run the code. Copy the below code and save it in a file called classpath.bat & run this batch file.

set HIBERNATE_HOME=C:\Hibernate\hibernate-distribution-3.6.0.Final
set CLASSPATH=%HIBERNATE_HOME%\hibernate3.jar;%HIBERNATE_HOME%\lib\required\dom4j-1.6.1.jar;%HIBERNATE_HOME%\lib\required\slf4j-api-1.6.1.jar;%HIBERNATE_HOME%\lib\jpa\hibernate-jpa-2.0-api-1.0.0.Final.jar;%HIBERNATE_HOME%\lib\required\commons-collections-3.1.jar;%HIBERNATE_HOME%\lib\required\javassist-3.12.0.GA.jar;%HIBERNATE_HOME%\lib\required\jta-1.1.jar;%HIBERNATE_HOME%\lib\required\antlr-2.7.6.jar;.;C:\PostgreSQL\postgresql-9.0-801.jdbc3.jar

Compile all the java files

C:\Hibernate\hibernate-distribution-3.6.0.Final\example\booksapp>javac -d . src\com\bookstore\*.java

Run the app

C:\Hibernate\hibernate-distribution-3.6.0.Final\example\booksapp>java com.bookstore.BookApp

Output

SLF4J: Failed to load class “org.slf4j.impl.StaticLoggerBinder”.
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

Hibernate: select max(BookId) from BookStore
Hibernate: insert into BookStore (BookName, AuthorName, BookCost, BookId) values (?, ?, ?, ?)
Hibernate: insert into BookStore (BookName, AuthorName, BookCost, BookId) values (?, ?, ?, ?)
Hibernate: insert into BookStore (BookName, AuthorName, BookCost, BookId) values (?, ?, ?, ?)
Hibernate: insert into BookStore (BookName, AuthorName, BookCost, BookId) values (?, ?, ?, ?)

Hibernate: select * from BookStore

BookName : Professional Hibernate ,AuthorName : Eric Pugh, Gradecki , BookCost : 350
BookName : Hibernate in Action ,AuthorName : Christian Bauer, Gavin King , BookCost : 499
BookName : Java Persistence With Hibernate ,AuthorName : Bauer, Gavin King , BookCost : 423
BookName : Begining Hibernate ,AuthorName : Dave Minter, Jeff Linwood , BookCost : 1500

Hibernate: select bookdetail0_.BookId as BookId0_, bookdetail0_.BookName as BookName0_, bookdetail0_.AuthorName as AuthorName0_, bookdetail0_.BookCost as BookCost0_ from BookStore bookdetail0_ where bookdetail0_.BookName=?
Getting Book Details using HQL.
[BookName : Hibernate in Action ,AuthorName : Christian Bauer, Gavin King , BookCost : 499]

Hibernate: select this_.BookId as BookId0_0_, this_.BookName as BookName0_0_, this_.AuthorName as AuthorName0_0_, this_.BookCost as BookCost0_0_ from BookStore this_ where this_.BookName=?
Getting Book Details using Criteria API.
[BookName : Hibernate in Action ,AuthorName : Christian Bauer, Gavin King , BookCost : 499]

Hibernate: select count(*) as col_0_0_ from BookStore bookdetail0_
Aggregate function count
[4]

Hibernate: select this_.BookId as BookId0_0_, this_.BookName as BookName0_0_, this_.AuthorName as AuthorName0_0_, this_.BookCost as BookCost0_0_ from BookStore this_ where this_.BookName=?
Hibernate: update BookStore set BookName=?, AuthorName=?, BookCost=? where BookId=?

Hibernate: select * from BookStore
BookName : Professional Hibernate ,AuthorName : Eric Pugh, Gradecki , BookCost : 350
BookName : Hibernate in Action ,AuthorName : Christian Bauer, Gavin King , BookCost : 499
BookName : Java Persistence With Hibernate ,AuthorName : Bauer, Gavin King , BookCost : 423
BookName : Begining Hibernate ,AuthorName : Dave Minter, Jeff Linwood , BookCost : 1000

Hibernate: select bookdetail0_.BookId as BookId0_, bookdetail0_.BookName as BookName0_, bookdetail0_.AuthorName as AuthorName0_, bookdetail0_.BookCost as BookCost0_ from BookStore bookdetail0_ where bookdetail0_.BookName=’Java Persistence With Hibernate’
delete : BookName : Java Persistence With Hibernate ,AuthorName : Bauer, Gavin King , BookCost : 423
Hibernate: delete from BookStore where BookId=?

Hibernate: select * from BookStore
BookName : Professional Hibernate ,AuthorName : Eric Pugh, Gradecki , BookCost : 350
BookName : Hibernate in Action ,AuthorName : Christian Bauer, Gavin King , BookCost : 499
BookName : Begining Hibernate ,AuthorName : Dave Minter, Jeff Linwood , BookCost : 1000

C:\Hibernate\hibernate-distribution-3.6.0.Final\example\booksapp>

Click here to view/download the source of book apps.

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