Listening for events

[Sloan Seaman <sl...@sgi.net>]

I have an object A, that uses log4j for various logging.

I have another object B, that I want to listen for any logging events within
A that are warning, errors, or fatals.

How do I registers B so that it will be informed when A does a log message?

Thanks!

--
Sloan


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Re: Listening for events

[Paul Smith <pa...@lawlex.com.au>]

On Wed, 2004-01-28 at 05:19, Sloan Seaman wrote:
> I have an object A, that uses log4j for various logging.
> 
> I have another object B, that I want to listen for any logging events within
> A that are warning, errors, or fatals.
> 
> How do I registers B so that it will be informed when A does a log message?

This should be straight forward.  Make B either extend from, or have an
inner-class that extends from the AppenderSkeleton class, and make B
register an instance of that inner class (or itself) as an appender on
the logger that A is is logging to.  That way B's inner class will
receive all the LoggingEvents objects for the logger A is logging to.

e.g.

class A{
 private static Logger LOG = Logger.getLogger(A.class);

 public void doSomething(){
  LOG.info("Hi there B!");
 }
}
......

class B{
 private BLogListener listener = new BLogListener();

 public B() {
  // register the internal ristener as an appender
   Logger.getLogger(A.class).addAppender(listener);
 }

 private void notifyBThatALoggedSomething(LoggingEvent e) {
  ....
 }


 private class BLogListener extends AppenderSkeleton {
   
  protected abstract void append(LoggingEvent event){
    notifyBThatALoggedSomething(event);
  }
 }
}


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