在 JSP 中使用 for 循环 [英] Using for loop inside of a JSP

问题描述

我想遍历Festivals"的 ArrayList 并使用 get 方法获取它们的信息，打印出它的所有值.出于某种原因，当我使用这段代码时，它总是会选择第0"个值而不是增加循环.

I want to loop through an ArrayList of "Festivals" and get their information with get methods, printing out all its values. For some reason when I use this code, it will always choose the "0"th value and not increment the loop.

如果我将值硬编码为get(1)"，它会得到正确的值，所以我的问题很明显是语法问题.

If I hard code the values as "get(1)" it will get the correct values so my issue is clearly with the syntax.

<h1>All Festival Information</h1>
    <jsp:useBean id="allFestivals" type="java.util.ArrayList" scope="session" />
    <table border="1">
        <tr>
            <td>Festival Name:</td>
            <td>Location:</td>
            <td>Start Date:</td>
            <td>End Date:</td>
            <td>URL:</td>
        </tr>
        <% for(int i = 0; i < allFestivals.size(); i+=1) { %>
            <tr>      
                <td>${allFestivals.get(i).getFestivalName()}</td>
                <td>${allFestivals.get(i).getLocation()}</td>
                <td>${allFestivals.get(i).getStartDate()}</td>
                <td>${allFestivals.get(i).getEndDate()}</td>
                <td>${allFestivals.get(i).getURL()}</td>  
            </tr>
        <% } %>
    </table> 

推荐答案

你的具体问题是因为你混合了 气馁和老派 scriptlets <% %> 及其后继EL ${}.它们不共享相同的变量作用域.allFestivals 在 scriptlet 范围内不可用，i 在 EL 范围内不可用.

You concrete problem is caused because you're mixing discouraged and old school scriptlets <% %> with its successor EL ${}. They do not share the same variable scope. The allFestivals is not available in scriptlet scope and the i is not available in EL scope.

您应该安装 JSTL(<-- 单击链接获取说明)并在 JSP 顶部将其声明为如下:

You should install JSTL (<-- click the link for instructions) and declare it in top of JSP as follows:

<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

然后按如下方式遍历列表:

and then iterate over the list as follows:

<c:forEach items="${allFestivals}" var="festival">
    <tr>      
        <td>${festival.festivalName}</td>
        <td>${festival.location}</td>
        <td>${festival.startDate}</td>
        <td>${festival.endDate}</td>
        <td>${festival.URL}</td>  
    </tr>
</c:forEach>

(注意可能的XSS 攻击漏洞，使用<c:out> 相应)

(beware of possible XSS attack holes, use <c:out> accordingly)

不要忘记删除 <jsp:useBean> 因为当您使用 servlet 作为模型和视图时，它在这里没有任何价值控制器.这只会导致混乱.另请参阅我们的 servlet wiki 页面.此外，您可以通过 web.xml 中的以下条目禁用 scriptlets，这样您就不会意外使用它们:

Don't forget to remove the <jsp:useBean> as it has no utter value here when you're using a servlet as model-and-view controller. It would only lead to confusion. See also our servlets wiki page. Further you would do yourself a favour to disable scriptlets by the following entry in web.xml so that you won't accidently use them:

<jsp-config>
    <jsp-property-group>
        <url-pattern>*.jsp</url-pattern>
        <scripting-invalid>true</scripting-invalid>
    </jsp-property-group>
</jsp-config>

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