好的，我已经阅读了很多，似乎找不到解决方法。
我有一个下拉菜单，我想确保在继续并提交表格之前有人更改/选择了答案。如果他们试图在未选择选择选项的情况下提交，我希望发出警报。
我尝试了多种要求的方式，例如：
th:required="required"，th:required="true"，required="required"，required="true" ...我什至在模型中尝试了@NoValidate注释。
如何使此下拉列表成为必需？谢谢！
<form class="ui form" th:object="${directBind}" th:action="directBind" method="post" style="padding:0 10px;">
<h4>Customer Setup</h4>
<div class="row">
<label >Contact Name (First/Last):</label>
<input type="text" th:field="*{contactName}" required="true" />
</div>
<div class="row">
<label for="formAddress">Address:</label>
<input type="text" id="formAddress" th:field="*{formAddress}" required="true"/>
</div>
<div class="row">
<label for="phoneNumber">Phone Number:</label>
<input type="text" id="phoneNumber" th:field="*{phoneNumber}" required="true"/>
</div>
<div class="row">
<label for="email">Email:</label>
<input type="email" id="email" th:field="*{email}" required="true"/>
</div>
<div class="row">
<label for="website" style="margin-top: 1em;"> Website:</label>
<input type="text" id="website" th:field="*{website}" required="true"/>
</div>
<div class="row">
<label for="nameInsured">Name Insured:</label>
<input type="text" id="nameInsured" th:field="*{insuredName}" required="true"/>
</div>
<div class="row">
<label>Business with Agency:</label>
<div th:each="businessAgency : ${businessAgencies}">
<input type="checkbox" th:field="*{businessAgencyList}" th:value="${businessAgency}"/>
<label th:text="${businessAgency}">Business with Agency</label>
</div>
</div>
<div class="row">
<label>Executive:</label>
<th:block th:switch="${loggedUser==null or loggedUser.client==null }">
<span th:case="false" th:text="${loggedUser.client.getExecutive()}"></span>
<span th:case="true"> Not Applicable </span>
</th:block>
<th:block th:switch="${loggedUser==null or loggedUser.client==null }">
<input th:case="false" type="hidden" name="executive" class="executive" th:value="${loggedUser.client.getExecutive()}" />
<input th:case="true" type="hidden" name="executive" class="executive" value="Not Applicable" />
</th:block>
<label style="font-size: 1.25rem; margin-left: 10px;">
<input type="checkbox" id="directBox" th:field="*{directBox}"/>
Direct </label>
</div>
<div class="row" style="display: inline-block; margin-top:0;">
<p>Service Level:</p>
<label>
<input type="checkbox" id="serviceLevel" th:field="*{serviceLevel}"/>
Affiliate Serviced</label>
</div>
<div class="row">
<label for="affiliateRep">Affiliate Designated Representative:</label>
<input type="text" id="affiliateRep" th:field="*{affiliateRep}" required="true" />
</div>
<div id="amsSection">
<h4 style="display: inline;">AMS360 Policy Setup</h4>
<input type="submit" formnovalidate="formnovalidate" name="addPolicy" class="btn btn-default" style="margin-left: 1rem; margin-bottom: 1rem;" value="Add Another Policy Line"/>
</div>
<div class="col-sm-12">
<hr/>
<table class="table table-striped AMSTable" data-classes="table-no-bordered" data-striped="true" data-show-columns="true" data-pagination="true">
<thead>
<tr>
<th>Policy Number</th>
<th>Policy Term Start Date</th>
<th>Policy Term End Date</th>
<th>Line of Coverage</th>
<th style="width:150px;">Parent Company<i class="tooltipped material-icons" data-position="top" data-tooltip="Parent Company indicates Standard Carrier, Wholesaler, or MGA">info_outline</i></th>
<th style="width:150px;">Writing Company<i class="tooltipped material-icons" data-position="top" data-tooltip="Writing Company indicates carrier paper specific to policy">info_outline</i></th>
<th>Bill Type</th>
<th>Quote Premium</th>
<th>Commission</th>
<th><a class="trigger btn btn-docModal"><span class="fa fa-upload"></span></a></th>
</tr>
</thead>
<tbody>
<tr name="newRow" th:each="ams360Policy,stat : ${ams360Policies}" th:value="${stat.index}">
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].policyNumber}"/></td>
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].policyTermDateStart}"/></td>
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].policyTermDateEnd}"/></td>
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].lineOfCoverage}"/></td>
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].parentCompany}"/></td>
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].writingCompany}"/></td>
<td id="billTypeCell">
<div th:each="billType : ${billTypeList}">
<input type="checkbox" th:field="*{ams360Policies[__${stat.index}__].billTypeOptions}" th:value="${billType}" value="off"/>
<label th:text="${billType}" id="billTypeLabel"></label>
</div>
</td>
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].quotePremium}"/></td>
<td> <input type="text" class="form-control" th:field="*{ams360Policies[__${stat.index}__].commission}"/></td>
<td class="text-right"> <button type="Submit" formnovalidate="formnovalidate" name="removeRow" th:value="${stat.index}" class="btn btn-danger" ><span class="fa fa-trash"></span></button></td>
</tr>
</tbody>
</table>
<table>
<tr>
<td id="appendFile"></td>
</tr>
</table>
</div>
<h4>PMA Setup</h4>
<div class="row" sec:authorize="hasAnyRole('ADMIN','USER')">
<label>Sub Brand:</label>
<th:block th:switch="${loggedUser==null or loggedUser.client==null }">
<span th:case="false" th:text="${loggedUser.client.getLegalName()}" ></span>
<span th:case="true">Not Applicable</span>
</th:block>
<th:block th:switch="${loggedUser==null or loggedUser.client==null}">
<input th:case="false" type="hidden" name="subBrand" class="subBrand" th:value="${loggedUser.client.getLegalName()}" />
<input th:case="true" type="hidden" name="subBrand" class="subBrand" value="Not Applicable" />
</th:block>
</div>
<!-- Business Class Drop Down Field Below: -->
<div class="row">
<label>Business Class: </label>
<div >
<select class="form-control" th:field="*{businessClasses}">
<option th:each="businessClass : ${businessClassList}" th:value="${businessClass}" th:text="${businessClass}"></option>
</select>
</div>
</div>
<div class="row">
<label for="descriptionOfOps">Description of Operations:</label>
<input type="text" id="descriptionOfOps" th:field="*{descriptionOfOps}" required="true" />
</div>
<div class="formFooter">
<input id="send" type="submit" value="send" name="send" class="btn btn-success finish" data-loading-text="Sent!" disabled="true"/>
</div>
</form>