如题,在这句,<c:if test="${param.submitted && empty param.userName}">
里面的empty param.userName, empty是什么语法呀?
**********************************************************************Example 8-5. Validating the name parameter with JSTL (validate_jstl.jsp)<%@ page contentType="text/html" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>User Info Entry Form</title>
</head>
<body bgcolor="white">
<form action="validate_jstl.jsp" method="post">
<input type="hidden" name="submitted" value="true">
<table>
<c:if test="${param.submitted && empty param.userName}">
<tr><td></td>
<td colspan="2"><font color="red">
Please enter your Name
</font></td></tr>
</c:if>
<tr>
<td>Name:</td>
<td>
<input type="text" name="userName"
value="<c:out value="${param.userName}" />">
</td>
</tr>
里面的empty param.userName, empty是什么语法呀?
**********************************************************************Example 8-5. Validating the name parameter with JSTL (validate_jstl.jsp)<%@ page contentType="text/html" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>User Info Entry Form</title>
</head>
<body bgcolor="white">
<form action="validate_jstl.jsp" method="post">
<input type="hidden" name="submitted" value="true">
<table>
<c:if test="${param.submitted && empty param.userName}">
<tr><td></td>
<td colspan="2"><font color="red">
Please enter your Name
</font></td></tr>
</c:if>
<tr>
<td>Name:</td>
<td>
<input type="text" name="userName"
value="<c:out value="${param.userName}" />">
</td>
</tr>
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