对于JSP中的选择框，reqest.getParameter（）返回null [英] reqest.getParameter() returns null for Select box in JSP
问题描述
我在jsp文件（在Adobe CQ上）中有以下代码，但它返回null。不知道为什么。
< select id =itemsperpage我预计out.println行会返回40，因为它是默认的选定值。 name =itemsperpage>
< option value =20> 20< / option>
< option value =40selected> 40< / option>
< option value =100> 100< / option>
< option value =200> 200< / option>
< / select>
<％
字符串itemsPerPage = request.getParameter（itemsperpage）;
out.println（Items：+ itemsPerPage）;
％>
您的代码将始终返回空。尝试在运行应用程序后看到页面源代码。 项目的值总是 null 。
请尝试以下代码：（在此代码中，每当combobox的值发生更改时，我都会发送一个请求）
< HTML>
< head>
< meta http-equiv =Content-Typecontent =text / html; charset = ISO-8859-1>
< title>在此插入标题< / title>
< / head>
< body onload =form1.submit（）;>
< form action =＃name =form1>
< select id =itemsperpagename =itemsperpageonchange =submit（）;>
< option value =20> 20< / option>
< option value =40selected> 40< / option>
< option value =100> 100< / option>
< option value =200> 200< / option>
< / select>
< / form>
<％
字符串itemsPerPage = request.getParameter（itemsperpage）;
out.println（Items：+ itemsPerPage）;
％>
< / body>
< / html>
[注意：我建议您不要使用 scriplets 在你的jsp文件中，而不是你可以去的AJAX，JSTL等]
I have the following code in a jsp file (on Adobe CQ) but, it returns null. Not sure why. I am expecting the out.println line to return 40 since it is the default selected value.
<select id="itemsperpage" name="itemsperpage">
<option value="20">20</option>
<option value="40" selected>40</option>
<option value="100">100</option>
<option value="200">200</option>
</select>
<%
String itemsPerPage = request.getParameter("itemsperpage");
out.println("Items: " + itemsPerPage );
%>
your code will always return null. try to see page source after running your application. value of Items is always null.
try following code: (in this code I am sending a request on every time the value of combobox is changed)
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body onload="form1.submit();">
<form action="#" name="form1">
<select id="itemsperpage" name="itemsperpage" onchange="submit();">
<option value="20">20</option>
<option value="40" selected>40</option>
<option value="100">100</option>
<option value="200">200</option>
</select>
</form>
<%
String itemsPerPage = request.getParameter("itemsperpage");
out.println("Items: " + itemsPerPage );
%>
</body>
</html>
[Note: i will suggest you to not use scriplets in your jsp file, instead you can go for AJAX , JSTL etc. ]
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