Thanks for a such response, but it doesn't work yet.
I tryied your solution, and it doesn't work, there is a problem in connection in these two lines :
DataSource ds = (DataSource)ctx.lookup("java:MySQLDB"); // Name used in *-ds.xml file
Connection con = ds.getConnection();
ds contain "org.jboss.resource.adapter.jdbc.WrapperDataSource@109afb8"
I substitued MySQLDB by the name in the xml (which is MySQLDB =] )
Where the problem may come from, maybe I forgot an important step...