In my project log4j is used extensively. Almost in all the action classes (we use struts), we log things. But the problem is, when concurrent users are there the logs are getting mixed up. Because of this debugging becomes a head-ache. I want to prefix all the logging statments with the userid of the person who has logged in. But its not possible to do this change in all the places where logging is used since I need to compile and deploy the whole application again which is impossible. Is there any way by which I can change some class or config file through which I can achieve my requirement?