无法从 JSP 读取表单值

发布于 2024-10-27 12:52:51 字数 2484 浏览 1 评论 0原文

我有一个 JSP 页面，其中有一个充满表单的表格。当我单击“提交”时，它会转到一个 servlet，该 servlet 应该使用 getParamValues 方法读取调查中表单的值，但它不起作用。当我尝试从 getParamValues 打印出字符串数组时，我不断收到 nullpointerExceptions。

这是相关的 servlet 代码：

public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
    resp.setContentType("text/plain");
    PrintWriter out = resp.getWriter();
    String[] nums = req.getParameterValues("questNum");
    out.println(nums[2]);
}

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
    doPost(req, resp);
}

这是相关的 JSP 代码，在 GAE 上运行：

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
 <%@ page import="com.surveycreator.service.persistence.SurveyPersistence" %>
 <%@ page import="com.surveycreator.service.model.Survey" %>
 <%@ page import="com.surveycreator.service.model.SurveyQuestion" %>
 <%@ page import="com.surveycreator.service.model.Survey" %>
 <%@ page import="java.util.List" %>


<html>
<head>
<link type="text/css" rel="stylesheet" href="/stylesheets/main.css" />
</head>

<body>
<p>View Survey</p>
<form action="/storesurvey" method="post">
<input type="submit" value="Submit Survey" />
</form>




<%
SurveyPersistence persist = new SurveyPersistence();
String surveyName = request.getParameter("content");
Survey survey = persist.getSurvey(surveyName);
List<SurveyQuestion> question = survey.getSurvey();
out.println("<table border='1'><tr><th>QuestionNumber</th><th>Survey Question</th><th>(Yes/yes)(No/no)</th></tr>");
for (SurveyQuestion questionObject : question) {
    int tableCounterString = questionObject.getQuestionNumber();
    String quest = questionObject.getQuestion();
    out.println("<tr><td><form><input id ='question' name='questNum' type='text' readonly='readonly' value='"+tableCounterString + " ' /></form></td><td><form><input id ='question' name='quest' type='text' readonly='readonly' value='"+quest + " ' /></form></td><td><form><input id ='ans' name='answer' type='text' value='' /></form></td></tr>");


}  


%>
<%= survey.getSurveyName()%>

</body>
</html>

原文

I have a JSP page which is a table full of forms. When I click submit it goes to a servlet which is suppose to read the values of the forms in the survey using the getParamValues method but it is not working. When I try to print out the String array from the getParamValues I keep getting nullpointerexceptions.

Here is the relevant servlet code:

public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
    resp.setContentType("text/plain");
    PrintWriter out = resp.getWriter();
    String[] nums = req.getParameterValues("questNum");
    out.println(nums[2]);
}

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
    doPost(req, resp);
}

Here is the relevant JSP code, running on GAE:

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
 <%@ page import="com.surveycreator.service.persistence.SurveyPersistence" %>
 <%@ page import="com.surveycreator.service.model.Survey" %>
 <%@ page import="com.surveycreator.service.model.SurveyQuestion" %>
 <%@ page import="com.surveycreator.service.model.Survey" %>
 <%@ page import="java.util.List" %>


<html>
<head>
<link type="text/css" rel="stylesheet" href="/stylesheets/main.css" />
</head>

<body>
<p>View Survey</p>
<form action="/storesurvey" method="post">
<input type="submit" value="Submit Survey" />
</form>




<%
SurveyPersistence persist = new SurveyPersistence();
String surveyName = request.getParameter("content");
Survey survey = persist.getSurvey(surveyName);
List<SurveyQuestion> question = survey.getSurvey();
out.println("<table border='1'><tr><th>QuestionNumber</th><th>Survey Question</th><th>(Yes/yes)(No/no)</th></tr>");
for (SurveyQuestion questionObject : question) {
    int tableCounterString = questionObject.getQuestionNumber();
    String quest = questionObject.getQuestion();
    out.println("<tr><td><form><input id ='question' name='questNum' type='text' readonly='readonly' value='"+tableCounterString + " ' /></form></td><td><form><input id ='question' name='quest' type='text' readonly='readonly' value='"+quest + " ' /></form></td><td><form><input id ='ans' name='answer' type='text' value='' /></form></td></tr>");


}  


%>
<%= survey.getSurveyName()%>

</body>
</html>

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微凉徒眸意 2024-11-03 12:52:51

根据目前提供的信息，NPE 的唯一可能原因是您根本没有任何、</code> 元素，在提交给 servlet 的 HTML 表单中的任意位置带有 <code>name="questNum"</code> 。

根据 JSP 代码更新：提交按钮确实采用与输入字段不同的 HTML 表单。您需要将提交按钮放在与输入字段相同的 HTML 表单中。根据功能需求（目前尚不清楚），您需要将提交按钮移动到表格单元格中，或者删除表格单元格中的

并包裹整个表格在一个大的内。

_{与具体问题无关，在这种特殊情况下混合使用 doGet() 和 doPost() 是一种糟糕的做法。如果您通过在浏览器地址栏中输入 URL 来打开 servlet，而不传递任何参数，那么您肯定会得到 NPE。不要让他们也这样做。仅使用 doGet() 来预处理请求，使用doPost()仅后处理请求。例如，JSP scriptlet <% %> 中的所有 Java 代码都应在 doGet() 中完成方法和 HTML 代码应通过 JSTL 标记重复。}

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七七 2024-11-03 12:52:51

我认为您的代码中有多种形式。当您按下“提交调查”按钮时，除了按钮的值之外，不会有任何值发送到 servlet。

解决方案：（根据您提供的代码）

     <head>
     <link type="text/css" rel="stylesheet"
 href="/stylesheets/main.css" />
     </head>

     <body>
     <p>View Survey</p>
     <form action="/storesurvey" method="post">
     <input type="submit" value="Submit Survey" />

     <%
     SurveyPersistence persist = new SurveyPersistence();
     String surveyName = request.getParameter("content");
     Survey survey = persist.getSurvey(surveyName);
     List<SurveyQuestion> question = survey.getSurvey();
     out.println("<table border='1'><tr><th>QuestionNumber</th><th>Survey Question</th><th>(Yes/yes)(No/no)</th></tr>");
     for (SurveyQuestion questionObject : question) {
         int tableCounterString = questionObject.getQuestionNumber();
         String quest = questionObject.getQuestion();
         out.println("<tr><td><input id
 ='question' name='questNum' type='text' readonly='readonly'
 value='"+tableCounterString + " '
 /></td><td><input id
 ='question' name='quest' type='text' readonly='readonly' value='"+quest + "
 ' /></form></td><td><input id
 ='ans' name='answer' type='text' value='' /></td></tr>");


     }  


     %>
</form> <-----(this is the change)
     <%= survey.getSurveyName()%>

     </body>
     </html>

请注意，我删除了您代码中的一些标签。

尝试一下。如果有bug，请在这里发帖。
希望这有帮助。

内森·潘

I think there are many forms in your code. when you press Submit Survey button, there is no value will be sent to the servlet but the value of button.

Solution: (base on your provided code )

     <head>
     <link type="text/css" rel="stylesheet"
 href="/stylesheets/main.css" />
     </head>

     <body>
     <p>View Survey</p>
     <form action="/storesurvey" method="post">
     <input type="submit" value="Submit Survey" />

     <%
     SurveyPersistence persist = new SurveyPersistence();
     String surveyName = request.getParameter("content");
     Survey survey = persist.getSurvey(surveyName);
     List<SurveyQuestion> question = survey.getSurvey();
     out.println("<table border='1'><tr><th>QuestionNumber</th><th>Survey Question</th><th>(Yes/yes)(No/no)</th></tr>");
     for (SurveyQuestion questionObject : question) {
         int tableCounterString = questionObject.getQuestionNumber();
         String quest = questionObject.getQuestion();
         out.println("<tr><td><input id
 ='question' name='questNum' type='text' readonly='readonly'
 value='"+tableCounterString + " '
 /></td><td><input id
 ='question' name='quest' type='text' readonly='readonly' value='"+quest + "
 ' /></form></td><td><input id
 ='ans' name='answer' type='text' value='' /></td></tr>");


     }  


     %>
</form> <-----(this is the change)
     <%= survey.getSurveyName()%>

     </body>
     </html>

Notice that I removed some tag in your code.

try it out. If there is bug, please post here.
Hope this help.

NathanPhan

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