You want to write a “page-composite” JSP that includes other pages or passes control to another page.
Suppose you have some common HTML code that you want to appear on every page, such as a navigator or header. You could copy it into each HTML and JSP file, but if it changed, you’d have to find all the files that used it and update each of them. It would be much easier to have one copy and include it everywhere you need it. Most webs servers feature such a mechanism already (e.g., server-side includes). However, using JSP’s mechanism has some advantages, such as the ability to attach objects to a request, a topic I’ll explore in Section 18.9.
The basic mechanism is simply to have
<jsp:include> with a PAGE attribute naming
the page to be included, and end with
</jsp:include>. For convenience, you can put
the / at the end of the opening tag and omit the closing tag. Much of
this syntax is taken from XML namespaces (see Chapter 21). The FLUSH attribute is also required, and
it must have the value TRUE; this is to remind you that, once you do
an include, the contents of the output are actually written.
Therefore, you can no longer do anything that involves sending
HTTP headers, such as changing content type
or transferring control using an HTTP redirect request. So a full JSP
include might look like this:
<H2>News of the day</H2> <jsp:include page="./news.jsp" flush="true" />
d request ...