JavaServer Pages, Second Edition

Including Page Fragments

You can use either a JSP directive or a standard action to include page fragments a JSP page. This is a useful technique when parts of all pages in an application are the same, such as headers, footers, and navigation bars.

The JSP include directive reads the content of the specified page in the translation phase (when the JSP page is converted into a servlet) and merges it with the original page:

<%@ include file="header.htmlf" %>

The file attribute is a relative path. If it starts with a slash, it’s a context-relative path, interpreted relative to the context path assigned for the application. If it doesn’t start with a slash, it’s a page-relative path, interpreted relative to the path for the page that includes the file.

The included file can contain either only static content (such as HTML) or it can be a regular JSP page. Its content is merged with the page that includes it, and the resulting page is converted into a servlet as described in Chapter 3. This means that the main page and all included pages share all page scope data. Scripting variables declared in JSP declarations, scriptlets, or actions, such as <jsp:useBean> or custom actions that introduce scripting variables, are also shared. Consequently, if the main page declares a variable, and the same name is used for another variable in an included page, it results in a translation phase error, because the combined page can’t be compiled.

One common use for the include directive is to include ...