jsp useBean 为 NULL 通过 servlet 的 getAttribute [英] jsp useBean is NULL by getAttribute by servlet
问题描述
用户在 servlet 中为空.如果做错了，请让我.
user is null in servlet. Pls let me if doing mistake.
我正在尝试获取 bean rateCode.jsp 中的所有 html 元素
i m trying to get all html element in bean rateCode.jsp
<%@page import="com.hermes.data.RateCode_" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Rate Code</title>
</head>
<body>
<jsp:useBean id="user" class="com.hermes.data.RateCode_" scope="request" >
<jsp:setProperty name="user" property="*"/></jsp:useBean>
<form id="f_rateCode" action="/ratePromoCodes" method="post" >
<table align="center" border="1" cellspacing="0">
<tr>
<td colspan="2" align="center" class="header">Rate Code Administrations</td>
</tr>
<tr>
<td align="right" style="border-style: solid;">Rate Code:</td>
<td align="left" style="border-style: solid;">
<input type="text" id="code" name="code" value="${user.code}" size="10" maxlength="32" style="width: 100px"/>
</td>
</tr>
<tr>
<td align="right" style="border-style: solid;">Rate Description:</td>
<td align="left" style="border-style: solid;">
<input type="text" id="description" name="description" value="<%=user.getDescription()%>" maxlength="128" size="40"></td>
</tr>
<tr><td><input type="submit" value="ok" /></td> </tr>
</table>
</form>
Servlet - ratePromoCodes
Servlet - ratePromoCodes
protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
RateCode_ rc = (RateCode_) req.getAttribute("user");
Enumeration an = req.getAttributeNames();
Enumeration pn = req.getParameterNames();
Object o = null;
while (an.hasMoreElements()) {
o = an.nextElement();
System.out.println(o);
}
while (pn.hasMoreElements()) {
o = pn.nextElement();
System.out.println(o);
}
}
RateCode.java (javaBean)
RateCode.java (javaBean)
public class RateCode_ {
private String code ;
private String description;
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
}
推荐答案
你似乎误解了 jsp:useBean 的工作和目的.
You seem to misunderstand the working and purpose of jsp:useBean.
首先，您已将 bean 声明为在会话范围内，并使用当前请求的所有参数填充它.
First of all, you've declared the bean to be in the session scope and you're filling it with all parameters of the current request.
<jsp:useBean id="user" class="com.hermes.data.RateCode_" scope="session">
<jsp:setProperty name="user" property="*"/>
</jsp:useBean>
这个 bean 被存储为 session 属性，名称为 user.您需要在 servlet 中作为会话属性而不是请求属性来检索它.
This bean is thus stored as session attribute with the name user. You need to retrieve it in the servlet as session attribute, not as request attribute.
RateCode_ user = (RateCode_) request.getSession().getAttribute("user");
(顺便说一下，user 是一个可怕且令人困惑的属性名称，我会将它重命名为 rateCode 之类的，没有这个奇怪的 _ 最后)
(user is a terrible and confusing attribute name by the way, I'd rename it rateCode or something, without this odd _ in the end)
但是，它不会包含任何内容.getCode() 和 getDescription() 将返回 null.<jsp:setProperty> 即没有用所有请求参数填充它，但此时您正试图在 servlet 中访问它.只有当您将包含参数的请求转发回 JSP 页面时，它才会这样做.然而，这超出了 servlet 中的业务逻辑.
However, it'll contain nothing. The getCode() and getDescription() will return null. The <jsp:setProperty> has namely not filled it with all request parameters yet at that point you're attempting to access it in the servlet. It will only do that when you forward the request containing the parameters back to the JSP page. However this takes place beyond the business logic in the servlet.
您需要自己收集它们作为请求参数.首先摆脱 JSP中整个<jsp:useBean>的东西，然后在servlet的doPost()方法中做如下操作:>
You need to gather them as request parameters yourself. First get rid of whole <jsp:useBean> thing in the JSP and do as follows in the servlet's doPost() method:
RateCode_ user = new RateCode_();
user.setCode(request.getParameter("code"));
user.setDescription(request.getParameter("description"));
// ...
request.setAttribute("user", user); // Do NOT store in session unless really necessary.
然后你可以在 JSP 中访问它，如下所示:
and then you can access it in the JSP as below:
<input type="text" name="code" value="${user.code}" />
<input type="text" name="description" value="${user.description}" />
(这仅对XSS 攻击敏感，你想安装JSTL并使用fn:escapeXml)
(this is only sensitive to XSS attacks, you'd like to install JSTL and use fn:escapeXml)
不，您不需要在 JSP 中需要
No, you do not need <jsp:useBean> in JSP. Keep it out, it has practically no value when you're using the MVC (level 2) approach with real servlets. The <jsp:useBean> is only useful for MV design (MVC level 1). To save boilerplate code of collecting request parameters, consider using a MVC framework or Apache Commons BeanUtils. See also below links for hints.
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