title: Update log4j within app and have log4j.properties updated
body: <p>I have multiple applications using log4j for their logging, each loading settings from separate log4j.properties loaded from the classpath (just a file on disk, not in a .jar or anything that would make it read-only).  In each of these applications, I want to allow updating the log level through the regular UI.</p>
  
  <p>I use a common utility class for this, which is shared between applications.  I can do that for the lifetime of the app, but since the changes aren't persisted back out to the appropriate log4j.properties file, on next restart, it's reset to the specific level in the properties file.  </p>
  
  <p>Since it's just loaded from the classpath, I don't know the full path to the logfile in each application, and since it's a common class, I'd rather not hardcode paths.  <strong>Is there a way to get log4j to write back its changes to its on-disk configuration?</strong></p>