How to load values in dropdown whose ID is not used…hide all records whose values are already used?

Question

This shows all the records.Please help me to show only the records whose id is not used ..

<select name="userDetailId" class="form-control" required>
          <option value="">Select</option>

         <c:forEach items="${userDetailList}" var="userDetail">

         <option value="${userDetail.userDetailId}" <c:if test="${userDetail.userDetailId == dataMap.userDetailId}"> selected </c:if> >${userDetail.name}</option>

         </c:forEach>
     </select>

Answer 1

Create some flag let's say isUsed and populate it's value as either true/ false ie used or not and add similar condition as below.

<select name="userDetailId" class="form-control" required>
          <option value="">Select</option>

         <c:forEach items="${userDetailList}" var="userDetail">
<c:if test="${isUsed}"> 
         <option value="${userDetail.userDetailId}" <c:if test="${userDetail.userDetailId == dataMap.userDetailId}"> selected </c:if> >${userDetail.name}</option>
</c:if> 
         </c:forEach>
     </select>