java 如何从java代码中的<select multiple>中检索多个选定的值？
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how to retrieve multiple selected values from <select multiple > in java code?
提问by Maddy.Shik
code is below:
代码如下：
<select name="merTransactionTypeId" class="cbox" multiple>
<!--
<option value="0" <%=request.getParameter("merTransactionTypeId")!=null?"0".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>All</option>
-->
<option value="2" <%=request.getParameter("merTransactionTypeId")!=null?"2".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>Reload</option>
<option value="1" <%=request.getParameter("merTransactionTypeId")!=null?"1".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>Sale</option>
<option value="5" <%=request.getParameter("merTransactionTypeId")!=null?"5".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>CCMS_Recharge</option>
<option value="6" <%=request.getParameter("merTransactionTypeId")!=null?"6".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>Loyalty_Award</option>
<option value="7" <%=request.getParameter("merTransactionTypeId")!=null?"7".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>Loyalty_Redeem</option>
<option value="16" <%=request.getParameter("merTransactionTypeId")!=null?"16".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>FCC_Reload</option>
<option value="11" <%=request.getParameter("merTransactionTypeId")!=null?"11".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>Tracking</option>
<option value="12" <%=request.getParameter("merTransactionTypeId")!=null?"12".equalsIgnoreCase(request.getParameter("merTransactionTypeId"))?"selected":"":""%>>Fund_Transfer_From_Card</option>
</select>
i am trying to retrieve values from dropdown with code in scriplet as
我正在尝试使用脚本中的代码从下拉列表中检索值
<% String[] selectedTransactionTypes = request.getParameterValues("merTransactionTypeId"); %>
...but it's returning null. Please help me out.
...但它返回空值。请帮帮我。
回答by BalusC
Apparently the listbox isn't enclosed in the same <form>, or there's even no means of a <form>, or maybe you tried to access it at the wrong moment (e.g. beforeform submit), or maybe there's a typo in the parameter name (use getParameterNames()to view them all).
显然列表框没有包含在同一个中<form>，或者甚至没有 a 的方法<form>，或者您可能在错误的时间尝试访问它（例如在表单提交之前），或者参数名称中可能有拼写错误（用于getParameterNames()查看商场）。
That said, I strongly recommend you to leave the old fashioned scriptlets aside and go ahead with a servlet class to preprocess and postprocess the request and taglibs/EL to control the flow and access data in JSP. It will make your code much cleaner.
也就是说，我强烈建议您将老式的 scriptlet 放在一边，继续使用 servlet 类来预处理和后处理请求，并使用 taglibs/EL 来控制 JSP 中的流和访问数据。它会让你的代码更简洁。
