How to configure DB through an environment variable?

I have a JSP application on multiple clients. Currently the database configuration is in a variavel.propriet file, and I get through the

private static String getUrlBanco() {        
    ResourceBundle b = ResourceBundle.getBundle("Base.variavel");
    return b.getString("urlbanco");
}

The problem is that it is not standard, the location of the base and the file is compressed along with the war, which forces me to generate one war per client.

I wanted a way to set this out of the application, I do not know, by environment variable, by setting in tomcat ...
I accept suggestions.