If you attempt to set the checkInterval init-param to 0 in jboss-web.deployer/conf/web.xml (4.2) or deployers/jbossweb.deployer/web.xml (5.1) you receive a warning 'Warning: Invalid value for the initParam checkInterval. Will use the default value of "300" seconds' despite the comments indicating it is a valid value.

What seems to have happened is that a while back we copied the org.apache.jasper.EmbeddedServletOptions class to org.jboss.web.tomcat.service.jasper.JspServletOptions so that we could override tldLocationsCache. Some time later, a Tomcat bug[0] in that class got fixed, but our copied code didn't get the fix applied.

The relevant change is removing the "if (this.checkInterval == 0)" block, so that 0 is an acceptable value. If we did want to disallow 0, then it is buggy because it gets left as 0 if the init-param is not present or is a non-numeric value.

[0] https://issues.apache.org/bugzilla/show_bug.cgi?id=41265