为什么提示Unknow tag (s:fildererror)
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="HelloAction" method="get">
用户名:<input type="text" name="name"/> <s:fildererror name="username" ></s:fildererror>
密码:<input type="password" name="psw" />
年龄:<input type="text" name="age" />
<input type="submit" value="提交">
</form>
</body>
</html>
提示：org.apache.jasper.JasperException: /login.jsp(12,37) No tag "fildererror" defined in tag library imported with prefix "s"
