How to change log level in log4j at runtime

Question

Hi,
I have a small requirement where the default log level is info, but if the user wants to invoke the Java program with debug level, the Debug should start off. I am trying to achieve this using this code..
          Logger root = Logger.getRootLogger();
          root.setLevel(Level.DEBUG);
          log.debug("This is debug");When I do this, the debug statement at the end does not print.
Then I thought may be the root logger level is not propagated after the initialization at start up, so I tried this
          log.setLevel(Level.DEBUG);
          log.info("This is info");
          log.debug("This is debug");
          log.info("Log level is " + log.getLevel());
          log.info(log.isDebugEnabled());The info statement prints "this is info" then the next info statement prints "log level is DEBUG" the next statement prints true but the intermediate debug statement does not print.
I have done this before in a Web app and it works just fine. I do not understand what is going on. Can someone please help me understand this.

Answer 1

I am not really familiar with Log4J, but in java.util.logging you define both a loglevel on the logger and the Handler that is actually responsible for outputting. A quick look on the Log4J sites shows that those are called 'appenders' in Log4J. So you might want to look if your appender is actually configured to output DEBUG-level statements.