Multi select Drop down in Struts2

<div class="select_wrap">
    <select name="sampleselect"  class="select_field" multiple="multiple" >

        <option>Select Id  </option>
        <s:iterator value="userList" var="usrList" status="s">
        <option value=<s:property value="#usrList"></s:property>><s:property value="#usrList"></s:property></option>

        </s:iterator>
    </select>
    </div>      
<br /><br />
            <s:submit value="Compliance Export" name="Export Data" align="left" action="exportExcelAction4"/>

usrList is getting populated from database

In my action class

private List<String> sampleselect=new ArrayList<String>();

    public List<String> getSampleselect() {
        return sampleselect;
    }


    public void setSampleselect(List<String> sampleselect) {
        this.sampleselect = sampleselect;
    }

But this sample select is not getting populated.