About the function equals must be used with a prefix when a default namespace are not specified resolve

This problem is typical of the Tomcat version conflict:
When using the El expression, it is not correct to determine whether the list is empty: ${list.size () > 0}, but it is OK to use in tomcat7, but it is not supported in Tomcat 6 and in previous versions. So when it is TOMCAT6, the project will not error, but the operation will be error.
The solution is also relatively simple: use the length method in the JSTL fn tag
First introduced in JSP <%@ taglib prefix= "FN" uri= "Http://java.sun.com/jsp/jstl/functions"%>
Then use ${fn:length (list) > 0}, this way is compatible.
Another is User.getname () This will also be an error.

About the function equals must be used with a prefix when a default namespace are not specified resolve