Monitoring Exceptions in Log Files

I am attempting to monitor the log file from our Jboss 4.2.2 server such that if a particular Java Exception occurs in the log file X times over a given time range (for example, 20 times in a 15 minute span) than raise an alert. I would like to apply similar (although with slightly different thresholds) to multiple Exceptions within the same log file

1) I tried using the File Monitor with Content Matching. The problem I encounter is that as soon as the matched contents occurs in the log file a single time, an alert is raised and the log file is marked as "Unavailable". I cannto see how to apply any sort of threshold to this.

2) I know that JBoss has the ability to raise SNMP Traps using log4j via "org.apache.log4j.ext.SNMPTrapAppender" OR JBoss can use a JMX Notifier using log4j via "org.jboss.monitor.services.JMXNotificationAppender", but I really have no idea how to make these work within Applications Manager.

What is the best approach to satisfy my Exception tracking requirement?

Thanks,
Mark