达到这种效果

<c:choose>
				<c:when test="${empty task.fileId}">   
	                          ------                         
	                       </c:when>
						   <c:otherwise>  
	                             ${task.fileId}
	                       </c:otherwise>

							</c:choose>

参考：http://576017120.iteye.com/blog/1949274