Tomcat 5.0.28 installed under LINUX - access to file system limited to tomcat user

[<Ekkehard.PETRI (at) ec.europa.eu>]

Hello

I have an installation of tomcat version 5.0.28 where tomcat runs under a user tomact on LINUX.
My jsp application should read files from a directory. Read access to directory and files is limited to group "sdf" and file owner "asd":
	drwxrws---   17 asd  	sdf  	data 				that contains the file
	-rwxrwx---      asd	sdf 	input.txt
The directory is owned by a different user than tomcat. However, user tomcat is a member of the group ("sdf" in the example) that owns the target directory. At LINUX level as user tomcat I have access to the file. For security reasons I cannot give read access to everybody.
With this set up of user rights my application cannot access the file. If I create a group "tomcat" and if I change owner and/or group of the directory and file to tomcat then the read access works.
Is this an error in my jsp application or could I configure tomcat that it would also read files without being the owner of files or the group?

Thank you very much for your help

Ekkehard