Yes possible,
try like:
in your validator add a field error:
ValidationUtils.rejectIfEmptyOrWhitespace(errors, "mainForm", "mainform.error.display.alternateText", "mainForm required!");
and in jsp you can show inside form the error like:
<c:set var="er"><form:errors path="mainForm"/></c:set>
<c:if test="${not empty er}">
<div class="alert alert-error">
<button type="button" class="close" data-dismiss="alert">×</button> <h4>Validation Error :</h4>
Please correct the following:<br/>
${er}
</div>
</c:if>