this document provides the basic information about hibernate. it's very useful while beginning with hibernate

1. An Introduction to Hibernate

2. Object-Relational Mapping Technique
Hibernate provides mapping between:
 Java Classes and the database tables.
 The Java data types and SQL data types.

3. Basic Architecture

5. Hibernate Configuration File
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD
3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3307/libms</property>
<property name="hibernate.connection.username">root</property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</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 stouts -->
<property name="show_sql">true</property>
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">update</property>
<mapping resource="com/myapp/struts/hbm/Staff.hbm.xml"/>
<mapping resource="com/myapp/struts/hbm/Department.hbm.xml"/>
</session-factory>
</hibernate-configuration>

6. Hibernate Mapping File
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//
Field Name Data Type EN"
"http://www.hibernate.org/dtd/hibernate-
Staff_id VARCHAR(1 mapping-3.0.dtd">
<hibernate-mapping>
0) <class name="com.myapp.struts.beans.Staff"
table=“Staff" catalog="libms">
Staff_name VARCHAR(3 <id name="StaffId" type="string">
0) <column name=“Staff_id" length=“10" />
<generator class="assigned" />
Staff_Depart VARCHAR(3 </id>
<property name=“StaffName"
ment 0) type="string">
<column name=“Staff_name"
length="30" not-null="true" />
</property>
<property name=“StaffDep" type="string">
<column name=“Staff_Department"
length=“30" />
</class>

7. public class Employee implements java.io.Serializable {
private String StaffId;
private String StaffName;
POJO private String StaffDep;
public Staff() {
<?xml version="1.0"?> }
public Staff(String id, String name) {
<!DOCTYPE hibernate-mapping PUBLIC
this. StaffId = id;
"-//Hibernate/Hibernate Mapping DTD this. StaffName = name;
3.0//EN" }
public Staff(String id, String name, String dep) {
"http://www.hibernate.org/dtd/hibernate-
this.id = id;
mapping-3.0.dtd"> this.name = name;
<hibernate-mapping> this. StaffDep = dep;
<class name="com.myapp.struts.beans.Staff" }
table=“Staff" catalog="libms">
public String getStaffId() {
<id name="StaffId" type="string"> return this. StaffId;
<column name=“Staff_id" length=“10" /> }
<generator class="assigned" /> public void setStaffId(String id) {
</id> this. StaffId = id;
}
<property name=“StaffName" type="string">
public String StaffName() {
<column name=“Staff_name" length="30" return this. StaffName;
not-null="true" /> }
public void set StaffName(String name) {
</property>
this. StaffName = name;
<property name=“StaffDep" type="string"> }
<column name=“Staff_Department" public String get StaffDep() {
return this. StaffDep;
length=“30" />
}
</class> public void set StaffDep(String department) {
</hibernate-mapping> this. StaffDep = department;
}

8. Basic APIs
 SessionFactory (org.hibernate.SessionFactory)
 Session (org.hibernate.Session)
 Persistent objects and collections
 Transient and detached objects and collections
 Transaction (org.hibernate.Transaction)
 ConnectionProvider
(org.hibernate.connection.ConnectionProvider)
 TransactionFactory (org.hibernate.TransactionFactory)

9. SessionFactory (org.hibernate.SessionFactory)
 A SessionFactory is an immutable, thread-safe object, intended
to be shared by all application threads. It is created once,
usually on application startup, from a Configuration instance.
 A org.hibernate.SessionFactory is used to obtain
org.hibernate.Session instances.
 HibernateUtil helper class that takes care of startup and makes
accessing the org.hibernate.SessionFactory more convenient.

10. HibernateUtil class
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static final SessionFactory sessionFactory = buildSessionFactory();
private static SessionFactory buildSessionFactory() {
try {
// Create the SessionFactory from hibernate.cfg.xml
return 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;
}
}

11. Session (org.hibernate.Session)
 A single-threaded, short-lived object representing a
conversation between the application and the persistent store.
Wraps a JDBC java.sql.Connection.
 Used for a single request, a conversation or a single unit of
work.
 A Session will not obtain a JDBC Connection, or a Datasource,
unless it is needed. It will not consume any resources until
used.

12. Persistent, Transient and Detached objects
 Transient - an object is transient if it has just been instantiated using
the new operator, and it is not associated with a Hibernate Session.
 Persistent - a persistent instance has a representation in the database
and an identifier value. It might just have been saved or loaded,
however, it is by definition in the scope of a Session. Hibernate will
detect any changes made to an object in persistent state and
synchronize the state with the database when the unit of work
completes.
 Detached - a detached instance is an object that has been persistent,
but its Session has been closed. The reference to the object is still
valid, of course, and the detached instance might even be modified in
this state. A detached instance can be reattached to a new Session at
a later point in time, making it (and all the modifications) persistent
again.

13. Transaction (org.hibernate.Transaction)
 A single-threaded, short-lived object used by the application to specify
atomic units of work. It abstracts the application from the underlying
JDBC, JTA or CORBA transaction.
 Security is provided by this API.

14. ConnectionProvider
(org.hibernate.connection.ConnectionProvider)
 A factory for, and pool of, JDBC connections. It abstracts the
application from underlying javax.sql.DataSource or
java.sql.DriverManager.

15. Extended Architecture

16. JSP Action Mapping Struts-config.xml Success/Failure
JSP
Fetch Values
Action Form
Refers
Action Class
Get Parameters
Set Parameters
Return Values
POJO
Invoke Methods
Update POJO
DAO Beans
Interacts
JDBC
Interacts
DATABASE

17. This was a short introduction of hibernate.
Want to know more?
Query me @ mohdzeeshansafi@yahoo.com
Special Thanks to Mr Asif Iqbal