第一步 导入包：<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn"%>

第二步：${fn:substring(str,0,10)} 

<select id="dataSourceId" name="dataSourceId">
<c:forEach items="${dataSourceConfigList}" var="dataSource">

    <c:choose>

        <c:when test="${dataSource.id eq datasource_id}">

            <option value="${dataSource.id}" selected="true">${dataSource.name}</option>

        </c:when>

        <c:otherwise>

            <option value="${dataSource.id}">${dataSource.name}</option>

        </c:otherwise>

    </c:choose>

</c:forEach>
</select>

<c:if test="${rows.theSame=='false'}">

    style="color:red"

</c:if>

<c:if test="${not empty 变量名称}">

代码.....

</c:if>