您好，我正在检查页面指令，但扩展页面指令不起作用。
下面是我的 jsp 页面
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page extends="javapackage.TestClass" %>
<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>Hai
<% out.println(show()); %>
</body>
</html>
我的类(class)是
package javapackage;
public class TestClass {
public String show(){
return "Welcome Prasad";
}
}
它给了我 500 错误
异常
org.apache.jasper.JasperException: java.lang.ClassCastException: org.apache.jsp.first_jsp cannot be cast to javax.servlet.Servlet
org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:177)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause
java.lang.ClassCastException: org.apache.jsp.first_jsp cannot be cast to javax.servlet.Servlet
org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:172)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
即使我尝试使用扩展 HttpServlet 的类，但没有用。所以请任何人帮助我。我正在使用 Tomcat 7
谢谢
最佳答案
您需要阅读 JSP 规范，特别是 JSP.11.2.4 部分，其中列出了与扩展一起使用的父类(super class)的许多要求，但您问题中的父类(super class)均不满足这些要求。
...the provided superclass:
- Implements HttpJspPage if the protocol is HTTP, or JspPage otherwise.
- All of the methods in the Servlet interface are declared final.
Additionally, it is the responsibility of the JSP page author that the provided superclass satisfies:
- The service method of the servlet API invokes the _jspService method.
- The init(ServletConfig) method stores the configuration, makes it available via getServletConfig, then invokes jspInit.
- The destroy method invokes jspDestroy.
关于java - 扩展页面指令不起作用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/26114432/