jstl foreach omit an element in last record

Just use LoopTagStatus#isLast().

<c:forEach items="${fileList}" var="current" varStatus="loop">
    { id: 1001,
      data: [
        "<c:out value="${current.fileName}" />",
        "<c:out value="${current.path}" />",
        "<c:out value="${current.size}" />",
        "<c:out value="${current.type}" />"
      ]
    }<c:if test="${!loop.last}">,</c:if>
</c:forEach>

You can also use the conditional operator in EL instead of <c:if>:

    ${!loop.last ? ',' : ''}