Kick starting with hibernate

ORM is no rocket science, it is a very useful tool though. The idea of a tool to help manage transactions and bean bindings is a developer's paradise. So how do we start off? Download hibernate from internet, along with it the not so obvious slf4j-simple-xxx.jar and slf4j-api-xxx.jar files are needed.

Place these in you project class path. The next step is writing the mapping files. The file hibernate.cfg.xml is the one which spells out the all encompassing details like those of the database, connection pool etc. The < entity >.hbm.xml files contain the object mapping information along any operation specific information.

A sample hibernate config xml for MySQL

<?xml version="1.0" encoding="UTF-8"?> <!-- Document : hibernate.cfg.xml.xml Created on : 02 November 2008, 19:31 Author : Kanthi Swaroop Rongala --> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <!-- Database connection settings --> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.url">jdbc:mysql://localhost/hospital_care</property> <property name="connection.username">root</property> <property name="connection.password"></property> <!-- JDBC connection pool (use the built-in) --> <property name="connection.pool_size">1</property> <!-- SQL dialect --> <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property> <!-- Enable Hibernate's automatic session context management --> <property name="current_session_context_class">thread</property> <!-- Disable the second-level cache <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property> --> <!-- Echo all executed SQL to stdout --> <property name="show_sql">true</property> <property name="format_sql">true</property> <!-- Drop and re-create the database schema on startup <property name="hbm2ddl.auto">create</property> --> <!-- <property name="transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property> --> <mapping resource="model/resources/Doctor.hbm.xml"/> <mapping resource="model/resources/Patient.hbm.xml"/> <mapping resource="model/resources/Appointment.hbm.xml"/> </session-factory> </hibernate-configuration>

Note that I have placed all my xmls in a different package called model.resources. What about the hibernate.cfg.xml location? We can move it as well.

See the following:

public class HibernateUtil { private static SessionFactory sessionFactory = null; private String CONFIG_FILE_PATH = "/model/resources/hibernate.cfg.xml"; private HibernateUtil(){ } private SessionFactory create() { try { // Create the SessionFactory from hibernate.cfg.xml sessionFactory = new Configuration().configure(CONFIG_FILE_PATH).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); } return sessionFactory; } public static SessionFactory getSessionFactory() { if(sessionFactory == null){ HibernateUtil utils = new HibernateUtil(); utils.create(); } return sessionFactory; } }

Hope this helps in giving you that well deserved push