关于src中${pageContext.request.contextPath}不能识别的问题

<form method="post" action="${pageContext.request.contextPath}/LoginServlet">
<label for="username"></label><input name="username" id="username"><br>
<label for="password"></label><input name="password" id="password"><br>
<input type="submit" value="登陆">
</form>
如果运行这一段代码的时候报错，请检查项目web.xmlwen文件的开头是这样的
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
<display-name>Archetype Created Web Application</display-name>
</web-app>改完记得重启