比较 JSP 中的字符串给出了非常奇怪的错误，没有说明是什么原因

Question

我正在比较 IF 块中的两个字符串，两个字符串都不为空，但显示了一个非常奇怪的错误。即使相同的代码仅使用 servlet 也能正常工作。但是当我运行这个代码在 JSP 时它给出了错误。我已经检查过值是否为空，但输出正是在表单中输入的内容。我的代码是这样

    <%
        String sender = (String) request.getAttribute("sender");
        System.out.println(request.getParameter("data") + "    " + request.getParameter("sender"));
        String process = "process";
        if (sender.equals(process)) {

            String itemName = request.getParameter("data");
    %>
            <%="No Item with name: " + itemName + " Found"%>
    <%
        }
    %>

这是显示的错误。

Some Error: An exception occurred processing [/error.jsp] at line [31] 28: String sender = (String) request.getAttribute("sender"); 29: System.out.println(request.getParameter("data") + " " + request.getParameter("sender")); 30: String process = "process"; 31: if (sender.equals(process)) { 32: 33: String itemName = request.getParameter("data"); 34: %> Stacktrace: org.apache.jasper.JasperException: An exception occurred processing [/error.jsp] at line [31] 28: String sender = (String) request.getAttribute("sender"); 29: System.out.println(request.getParameter("data") + " " + request.getParameter("sender")); 30: String process = "process"; 31: if (sender.equals(process)) { 32: 33: String itemName = request.getParameter("data"); 34: %> Stacktrace: [Ljava.lang.StackTraceElement;@6fb251a5

以下是我的完整页面代码

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!doctype html>
<html class="no-js" lang="">
<head>
    <meta charset="utf-8">
    <title>No Data</title>

    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="css/normalize.css">
    <link rel="stylesheet" href="css/main.css">

    <meta name="theme-color" content="#fafafa">
</head>
<body>
   <section id="google-form" class="section google-form">
      <div class="account_create-text center  ">
         <h4>Oops No data found. </h4>
      </div>
      <br>

      <span class="username_curr-email blue ce block spacer-10">!
      <%
           String sender = (String) request.getAttribute("sender");
           System.out.println(request.getParameter("data") + "    " + request.getParameter("sender"));
           String process = "process";
           if (sender.equals(process)) {

               String itemName = request.getParameter("data");
       %>
               <%="No Item with name: " + itemName + " Found"%>
       <%
           }
       %>
       </span>
       <span class="spacer-10 block"></span>
       <span class="spacer-10 block"></span>
       <span class="spacer-10 block"></span>
      <br>
      <br>
      <br>
      <div class="bb-30 spacer-10">
          <a href="Task1.html" style="text-decoration: none;" class="button-elevated ">
              Go back
          </a>

      </div>
     <br>
     <br>


 </section>
 </body>

 </html>

Answer 1

找到答案了。使用错误的方法。

request.getParameter()

应该用过

比较 JSP 中的字符串给出了非常奇怪的错误，没有说明是什么原因

Comparing strings in JSP gives really weird error not specyfying what can e the cause

java

jsp