Code Not Saving Data To Database

I have a simple project to save data to the database. I have successfully mapped the java class with the database table. The code displays no error, it runs very well but it does not save to database, instead it catches an exception and prints out "saving failed". The database is a mysql database.

This is the managed bean code. Save.java(name=bean)
 
//imports
 
@ManagedBean(name="bean")
@RequestScoped
public class Save { 
private String username,password,msg;
Session session = null;
Transaction transaction = null;
//GETTERS AND SETTERS
public Save() {

[Code] ....

This is a screenshot of my Hibernate configuration file : hb.jpg