java.lang.Error：JSP中发生无法解决的编译错误

小编典典

java.lang.Error：JSP中发生无法解决的编译错误

jsp

在本教程中编写了相同的代码后，我尝试遵循有关JSP和eve的教程，但仍然收到以下错误。

java.lang.Error：未解决的编译问题：重复的局部变量cart。

我正在尝试使用以下代码运行servlet。

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();

        Cart cart = (Cart)session.getAttribute("cart");

        if (cart == null) {
            cart = new Cart();  
        }

        cart.setTotalItems(7);

        session.setAttribute("cart", cart);
        getServletContext().getRequestDispatcher("/showcart.jsp").forward(request,response);

    }


HTTP Status 500 - Servlet execution threw an exception

--------------------------------------------------------------------------------

type Exception report

message Servlet execution threw an exception

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)


root cause

java.lang.Error: Unresolved compilation problem: 
Duplicate local variable cart

demo.Session.doGet(Session.java:32)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

note注意在Apache Tomcat / 7.0.53日志中可以找到根本原因的完整堆栈跟踪。

Apache Tomcat / 7.0.53

showcart.jsp：

<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"            "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Insert title here</title>
</head>
<body>
<%@ page import= "demo.*" %>

<% Cart cart= (Cart)session.getAttribute("cart");%>

Items in cart : <%= cart.getTotalItems() %>
</body>
</html>

web.xml：

<servlet>
    <description></description>
    <display-name>Session</display-name>
    <servlet-name>Session</servlet-name>
    <servlet-class>demo.Session</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Session</servlet-name>
    <url-pattern>/Session</url-pattern>
  </servlet-mapping>
 </web-app>

session.java

package demo;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class Session
 */
public class Session extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Session() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();

        Cart cart = (Cart)session.getAttribute("cart");

        if (cart == null) {
            cart = new Cart();  
        }

        cart.setTotalItems(7);

        session.setAttribute("cart", cart);
        getServletContext().getRequestDispatcher("/showcart.jsp").forward(request,response);

    }


    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

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2020-06-10

共1个答案

小编典典

由于您在运行时而不是编译时遇到错误，因此我认为问题不必与显示的代码直接相关（如果有的话）。该代码是在打包WAR文件时而不是在部署WAR文件时编译的，如果您获得了WAR，我认为它可以很好地编译。

我猜这个重复的变量是在JSP文件中定义的，它恰好也有一个名为“
cart”的变量。JSP文件通常在第一个请求时在运行时“即时”编译。如果您查看，showcart.jsp您应该看到真正的原因。堆栈跟踪似乎支持这一点，你可以验证我通过重命名说cart的doGet方法别的东西-
错误还是会说“购物车”。如果您没有在中找到原因showcart.jsp，可以将其内容张贴出来吗？

2020-06-10