The java objects instantiated for JSP Custom Tags can now be pooled and reused. This significantly boosts the performance of JSP pages which use custom tags.
That page also says that web.xml can contain an "enablePooling" option for that, and that its default value is true.
After the doEndTag invocation, the tag handler is available for further invocations (and it is expected to have retained its properties). So what I do is reset all local variables to their default value just before doEndTag() returns