jsp页面中几种标签的引用方式

<%@ page language="java" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>
<%@ taglib prefix="s" uri="/struts-tags" %>
<%@ taglib uri="http://displaytag.sf.net" prefix="display"%>
<%@ taglib uri="http://www.extremecomponents.org" prefix="ec" %>

<c:set var="ctx" value="${pageContext.request.contextPath}"/>