Is it possible to write a Linux/Unix/Win2k service that interfaces with a Java application that captures write outputs from another application, say a log file, and creates a copy of the write stream to another file?

In other words, I want a service to "listen" for writes into a file call err.log...Err.log is a proprietary and needed file for the application writing to it. I want to be able to get the stream from the OS and write to another file so I can do work against it with anothe application.