logging in java apps

for starter, lets begin with java.util.logging..

http://www.java-tips.org/java-se-tips/java.util.logging/how-to-use-logger.html
http://www.rgagnon.com/javadetails/java-0501.html
http://www.roseindia.net/java/example/java/util/quintessential-logging-program.shtml

and log4j..
http://logging.apache.org/log4j/1.2/manual.html
http://www.basilv.com/psd/blog/2006/tips-for-using-log4j
http://homepage.mac.com/kelleherk/iblog/C1837526061/E2136921646/index.html

the interface:

package org.apache.log4j;

 public class Logger {

   // Creation & retrieval methods:
   public static Logger getRootLogger();
   public static Logger getLogger(String name);

   // printing methods:
   public void trace(Object message);
   public void debug(Object message);
   public void info(Object message);
   public void warn(Object message);
   public void error(Object message);
   public void fatal(Object message);

   // generic printing method:
   public void log(Level l, Object message);
}