Java ee el Expression

In the past when developing, occasionally encountered JSP page does not support El expression case.

The reason for this is that the El function is turned off,

The solution at the time was to turn off ignore. Iselignored Set

But why don't you have to set it sometimes? It was found to be related to the declaration of Web. Xml.

Some versions of Servlet declarations are turned off by default.

Looks like it needs to be added before 2.4.

<%@ page iselignored= "false"%>