I’m posting this because I always spend half-an-hour trying to find this information. To set up virtual mappings or virtual directories (what I call them) for ColdFusion on JRun on OSX, edit the jrun-web.xml file in (this is where mine was, you may have to look elsewhere):
/Applications/JRun4/servers/cfusion/cfusion-ear/cfusion-war/WEB-INF/jrun-web.xml
Add an entry to the jrun-web-app xml element like this…
<jrun-web-app>
<!-- ... -->
<virtual-mapping>
<resource-path>/virtualdir/*</resource-path>
<system-path>/physical/path/</system-path>
</virtual-mapping>
<!-- ... -->
</jrun-web-app>