You can use variables to give virtual-server specific values for a class without having to define each value individually. A variable is defined in the obj.conf file. You can define your own variables, but the user interface will not recognize them. The variable that is most useful in the user interface is the variable $id, which represents the ID of the virtual server. Whenever you enter this variable, the server substitutes the value for the individual virtual server ID.
There are a few other variables, such as $accesslog (the path to each virtual server’s access log) and $docroot (the path to each virtual server’s document root), that you may occasionally see, but $id is the only one you should need to enter into a field.
For more information on variables, see the Sun Java System Web Server 6.1 SP12 NSAPI Programmer’s Guide.