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Chapter 12 Including Files and Applets in JSP Documents

12.1 Including Files at Page 

Translation Time

You use the 

include

 directive to include a file in the main JSP document at

the time the document is translated into a servlet (which is typically the first

time it is accessed). The syntax is as follows:

<%@ include file="Relative URL" %>

There are two ramifications of the fact that the included file is inserted at

page translation time, not at request time as with 

jsp:include

  (Section

12.2).

First, you include the actual file itself, unlike with 

jsp:include

 , where

the server runs the page and inserts its output. This approach means that the

included file can contain JSP constructs (such as field or method declara 

tions) that affect the main page as a whole.

Second, if the included file changes, all the JSP files that use it need to be

updated. Unfortunately, although servers are allowed to support a mecha 

nism for detecting when an included file has changed (and then recompiling

the servlet), they are not required to do so. In practice, few servers support

this capability. Furthermore, there is not a simple and portable  retranslate

this JSP page now  command. Instead, you have to update the modification

date of the JSP page. Some operating systems have commands that update

the modification date without your actually editing the file (e.g., the Unix

touch

 command), but a simple portable alternative is to include a JSP com 

ment in the top level page. Update the comment whenever the included file

changes. For example, you might put the modification date of the included

file in the comment, as below.

<%   Navbar.jsp modified 3/1/00   %>

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

Core Warning

If you change an included JSP file, you must update the modification dates 

of all JSP files that use it.

For example, Listing 12.1 shows a page fragment that gives corporate con 

tact information and some per page access statistics appropriate to be

included at the bottom of multiple pages within a site. Listing 12.2 shows a

page that makes use of it, and Figure 12 1 shows the result.

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

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