Dynamic changes in config file

Hi:
Here's a trivial question. I've read the documentation but I didn't find anything about this topic. Are the changes to the configuration file (either property based or xml), automatically reflected to the library ? 
I mean does log4cxx detect when a configuration file is changed, and then reloads the config info ? or do I have to restart the application that uses the library in order to change, let's say: a Log Level, or the type of an Appender ?
thanks in advance !

Diego Susa
www.cestel.es