如何使用Struts2使列表类型的变量为空 <s:if> 标签

Question

I have list of Payment Gateway retrieved from requestAttribute on my Jsp as below :

List<String> payGwList = (List<String>)request.getAttribute("payGwList");

I have to populate them in my select-box(combo-box) but before that have to do following check

EDIT

1. Null Check
2. size > 1 Check

My Code is :

<%
 <%if(payGwList != null && payGwList.size() > 1){ //edited
%>
    <tr id="paygwrowid" >
    <td width="112" class="content">
        <s:label key="payment.paymentgateway"/><span class="requiredData">*</span>
    </td>
    <td colspan="2" class="content">
        <select name="paymentGateway" id="paymentGateway" class="content" style="width:189px;">
                <option value="0">--Select--</option>
            <%if(payGwList != null && !payGwList.isEmpty()){                    
                for(String paymentGateway : payGwList){  
            %>
                <option value="<%=paymentGateway%>"><%= paymentGateway%></option>                       
            <%}}%>
        </select>
    </td>
    </tr>
<%}%>

But how to do achieve the same using <s:if> tag as i dont want to use scriptlets on my jsp.

Answer 1

<% if(payGwList != null){ %> = <s:if test="payGwList != null"> , while

<select name="paymentGateway" id="paymentGateway" class="content" style="width:189px;">
        <option value="0">--Select--</option>
    <%if(payGwList != null && !payGwList.isEmpty()){                    
        for(String paymentGateway : payGwList){  
    %>
        <option value="<%=paymentGateway%>"><%= paymentGateway%></option>                       
    <%}}%>
</select>

becomes simply

<s:select list = "payGwList"
       listKey = "paymentGateway"
     listValue = "paymentGateway"
     headerKey = "0"
   headerValue = "--Select--"
          name = "paymentGateway" 
            id = "paymentGateway" 
      cssClass = "content" 
      cssStyle = "width: 189px;" 
/>

listValue and listKey are not even necessary here because you are using the same value for both of them.

Avoid Scritplets and be sure to use all the power of the framework through its UI Tags too.