Exception Notification in Java

Are there any good exception notification systems for web apps using Tomcat? Looking for libraries equivalent of exception_not开发者_C百科ification etc. which are available as plugins for Rails.

Have a look at http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/net/SMTPAppender.html from log4j and also an extension I'm describing at http://blog.cherouvim.com/a-better-smtpappender/