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Tags/Keywords : Hibernate Session,Contextual-Session,Example-Case-study
Author : Amit
Date (Year/Month/Date): 2009-04-18
Example showing ManagedSessionContext

Example on using Hibernate JDBCTransaction and current session API for 
using a single Hibernate Session and JDBCTransaction from
managed as current_session_context_class and using Hibernate
ManagedSessionContext .

A very simple commandline based Java application, that uses a configuration
XML file (example.xml) to read all properties for creation of SessionFactory,
and a HBM XML file for mapping a class (example.User) to persistent Table "User".

example.xml
tr>

<?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>

        <!-- Database connection settings -->
        <property name="connection.driver_class">
                  org.hsqldb.jdbcDriver
        </property>
        <property name="connection.url">
                  jdbc:hsqldb:hsql://localhost
        </property>
        <property name="connection.username">sa</property>
        <property name="connection.password"></property>

        <!-- SQL dialect -->
        <property name="dialect">
                  org.hibernate.dialect.HSQLDialect
        </property>

        <!-- Enable managed session context management -->
        <property name="transaction.factory_class">
                  org.hibernate.transaction.JDBCTransactionFactory
        </property>
        <property name="current_session_context_class">
                  managed
        </property>

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

        <mapping resource="User.hbm.xml"/>

    </session-factory>

</hibernate-configuration>





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This example.xml file will be read by the TestClient main program
and build Hibernate SessionFactory as shown below:
example.TestClient.java
tr>

package example;
import org.hibernate.*;
import org.hibernate.engine.*;
import org.hibernate.cfg.*;
import org.hibernate.context.*;
public class TestClient
{
SessionFactory sessFactory;
Session session;
public TestClient() {
    try{
        Configuration conf = new Configuration();
        sessFactory = conf.configure("example.xml").buildSessionFactory();
	//ManagedSessionContext is created
	//by using SessionFactoryImplementor
        ManagedSessionContext managedSession = 
	  new ManagedSessionContext((SessionFactoryImplementor)sessFactory);
	//Hibernate Session is opened and
	//bound to the ManagedSessionContext
        managedSession.bind(sessFactory.openSession());

        //From ManagedSessionContext a Hibernate
	Session can be obtained by using currentSession
        session = managedSession.currentSession();
        session.beginTransaction();
        User user = new User();
        user.setUserId("100C");
        user.setName("created");
        saveUserInfo(user);
        user.setName("modified");
        updateUserInfo(user);
        session.getTransaction().commit();
    } catch (Exception ex) {
        session.getTransaction().rollback();
        ex.printStackTrace();
    } finally {
        session.close();
    }
}
   /**
    *  Method that uses SessionFactory getCurrentSession 
    *  to persist User into database table.
    */
    public void saveUserInfo(User argUser) {
        Session localSession = sessFactory.getCurrentSession();
        System.out.println(localSession.getTransaction());
        localSession.save(argUser);
    }
    public void updateUserInfo(User argUser) {
        Session localSession = sessFactory.getCurrentSession();
        System.out.println(localSession.getTransaction());
        localSession.update(argUser);
    }
    public static void main(String[] args) 
    {
        new TestClient();
    }
}



All supporting information for storing User object to User table are
listed below:
SQL
create table User
(user_id varchar(100), user_name  varchar(100), primary key(user_id));

example.User
package example;

public class User
{
	private String userId;
	private String name;
    public void setUserId(String argUserId) {
		userId = argUserId;
	}
	public String getUserId() {
		return userId;
	}
	public void setName(String argName) {
		name = argName;
	}
	public String getName() {
		return name;
	}
}


User.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="example">
  <class name="User" table="User">
        <id name="userId" access="property" column="user_id"/>
        <property name="name" column="user_name"/>
  </class>
</hibernate-mapping>



After going through the TestClient, one can very well understand
objective of this example.

Let me explain a bit:

1. current_session_context_class as "managed"
   and ManagedSessionContext provides a way to use getCurrentSession
   method of Hibernate SessionFactory in this Java command line application.
2. So JDBCTransaction has to be started/begin at some point of time, and
   will be available in two operations, such as saveUserInfo and updateUserInfo.
3. Once transaction is committed or rollback, Hibernate Session will be
   flushed. In finally block, Hibernate Session is closed.

This example is trying to show a simple way to use Managed Session context
with a JDBCTransaction and using a single Session and Transaction for
multiple operations in form a single block of task.

After compiling and running this TestClient, following is the output
on console:


org.hibernate.transaction.JDBCTransaction@a761fe
org.hibernate.transaction.JDBCTransaction@a761fe
Hibernate: insert into User (user_name, user_id) values (?, ?)
Hibernate: update User set user_name=? where user_id=?


This output show that same JDBCTransaction is being used in both the 
operations, as the System.out.println for the Transaction, comes out
to be same.

Any questions from reader will be highly appreciated, and I would like
to discuss more on improving this example with your suggestions.
Thanks for reading this example.



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