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Java Cookbook by Ian F. Darwin

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JSP Include/Forward

Problem

You want to write a “page-composite” JSP that includes other pages or passes control to another page.

Solution

Use <jsp:include> or <jsp:forward>.

Discussion

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" />

The jsp:forwar d request ...

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