Difference b/w include directive and jsp:include tag

The jsp:include tag is handled at request time. For every request that comes in for the index.jsp URL, the content.jsp servlet will be run when the jsp:include tag is encountered. In principle, this could have been done at translation time; the chunk of HTML from the content.jsp file could have been dropped right into the index.jsp servlet. This would be much less powerful, however. By processing includes at request time, the contents of the included file can change independently of the main file.

<%@include file="contents.jsp" %>

This tag is called a directive because it directs the page compiler to take some action. In this case, when it sees the directive, the page compiler will embed the contents of the contents.jsp file directly into the servlet that it is building for index.jsp. Subsequently, if the contents.jsp file is edited, index.jsp will not change. Browsers will continue to get the old message until the page compiler is forced to rebuild the index.jsp servlet.

Note- that the include directive specifies what is to be included with file=, whereas the jsp:include tag specifies page=. This nicely encapsulates the differences between the two: The directive includes a file as it is building the servlet at request time, and the tag includes another page at request time.