jmx monitoring of the appserver jvms.
if you have 8.5.01.002+ you can scrape the appserver logs.
i'd played around w/ jmxtrans which is an open source jmx agent and graphite for the graphing but haven't had time to flush it all out. but any jmx tool (not just the jmxcli), time-series db and graphing tool would work.
Unfortunately we're still at 8.3.03.116 in prod...
The jmx monitoring will work in any version
Will give that a try then.