one reason jstl cannot be resolved in either

The absolute uri: http://java.sun.com/jsp/jstl/core cannot be resolved in either

在web.xml中增加如下配置即可：
<jsp-config>
<taglib>
      <taglib-uri>http://java.sun.com/jsp/jstl/core</taglib-uri>
      <taglib-location>/WEB-INF/tld/c.tld</taglib-location>
  </taglib>

<taglib>
      <taglib-uri>http://java.sun.com/jsp/jstl/functions</taglib-uri>
      <taglib-location>/WEB-INF/tld/fn.tld</taglib-location>
  </taglib>
  <taglib>
      <taglib-uri>http://java.sun.com/jstl/fmt_rt</taglib-uri>
      <taglib-location>/WEB-INF/tld/fmt-1_0-rt</taglib-location>
  </taglib>
  </jsp-config>