How to use format date as “yyyy-MM-dd” with JSTL? [duplicate]

Answer 1

First you need to add the line below to head of your jsp file

<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>

Now you can use <fmt:formatDate> and <fmt:parseDate> for formatting date.

<fmt:formatDate value="${now}" pattern="yy-MMM-dd"/>

PS: In your code, I saw you had some mistakes with the jsp tag. I think it should be

    <div class="form-group">
      <span><fmt:message key="task.start"/></span>
      <input class="form-control" id="firstDate" placeholder="<fmt:message key='task.start'/>" 
           name="start_date-${task.taskId}" value="<fmt:formatDate value='${task.startDate}' var='startFormat' type='date' pattern='yyyy-MM-dd'/>"
   </div>

Answer 2

The value for fmt:formatDate is suppose to be a Date object (java.util.Date). If the task.startDate is a date as a String, then you need to convert it beforehand.

<fmt:parseDate value="${task.startDate}" pattern="yyyy-MM-dd HH:mm:ss" var="myDate"/>
<fmt:formatDate value="${myDate}" var="startFormat" pattern="yyyy-MM-dd"/>