Convenience base class for Resource implementations,
pre-implementing typical behavior.
The "exists" method will check whether a File or InputStream can
be opened; "isOpen" will always return false; "getURL" and "getFile"
throw an exception; and "toString" will return the description.
The "exists" method will check whether a File or InputStream can be opened; "isOpen" will always return false; "getURL" and "getFile" throw an exception; and "toString" will return the description.