Pass an application with the possibility to change context.xml

[Weldzar]

Well, I'm a newbie of creating web application ( and maybe of creating application in general )...
however the problem is that I would have to pass and execute an application in an other system where the username and password, used to access the MySql database, could be different..

For that I know, I would have to create a .war of the application, but how could I modify easily username and password used in the application to access the database of other systems?

Is there a typical way to treat problem like that or have I missed something to do?

Thank you and sorry for my poor English..