First you need to declare your resources in dispatcher-servlet file like this :
<mvc:resources mapping="/resources/**" location="/resources/folder/" />
Any request with url mapping /resources/** will directly look for /resources/folder/.
Now in jsp file you need to include your css file like this :
<link href="https://stackoverflow.com/questions/26276603/<c:url value="/resources/css/main.css" />" rel="stylesheet">
Similarly you can include js files.
Hope this solves your problem.