可输入下拉框，jquery.editable-select

//须引入jquery和以下
<link rel="stylesheet" type="text/css" href="jquery.editable-select.min.css"/>
<script type="text/javascript" src="jquery.editable-select.min.js"></script>


<select class="form-control" name="entity.contractCode" id="contractCode" value="${entity.contractCode}">
 <s:iterator value="contractCodeList">
    <s:if test="not empty entity.contractCode">
        <option value="${entity.contractCode}" selected>${entity.contractCode}</option>
    </s:if>
    <s:else>
        <option value="${value}">${value}</option>
    </s:else>
</s:iterator>
</select>

setSelectedOption("#contractCode",contractCode);
$(‘#contractCode‘).editableSelect({
    effects: ‘slide‘,
    //可选参数default、fade
    filter: false,// 不过滤，否则选中后其它选项消失
});


function setSelectedOption(selector, value){
    if (value.length !=0) {
        $(selector +" > option[value=‘"+value+"‘]").attr("selected",true);
    }
}