session/transction mandatory when calling UserModule/RoleMod

[je.a.le]

I only need read only operations like getting list of role, user, etc...
I notice that in order for a "MBeanProxy" to works, the call must be done inside a session (ok) but into a transaction too (?)

here a working code :

Session session = null;
Transaction t = null;
 try {
 SessionFactory identitySessionFactory = (SessionFactory) new InitialContext().lookup("java:/portal/IdentitySessionFactory");
 session = identitySessionFactory.openSession();
 t = session.beginTransaction();

 MBeanServer mbeanServer = MBeanServerLocator.locateJBoss();
 RoleModule roleModule = (RoleModule) MBeanProxy.get(RoleModule.class,
 new ObjectName("portal:service=Module,type=Role"), mbeanServer);

 Set s = roleModule.findRoles();
 Iterator it = s.iterator();
 while (it.hasNext()) {
 // just dump role for the test
 System.out.println("roles : " + it.next());
 }
 } catch (Exception ex) {
 ex.printStackTrace();
 } finally {
 if (t != null) {t.rollback(); }
 if (session != null) {session.close();}
 }

It's strange to start a transaction and always call a roolback !?!
Am I actually making the request right !???

My code will not be call from a protlet, mostly servlet/dwr.
anyway adding a trans-attribute to portlet.xml doesn't work for me.

<transaction>
 <trans-attribute>Required</trans-attribute>
</transaction>

Thanks