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Directive tag ( <%@ directive ... %>)
A JSP directive gives special information about the page to the JSP Engine.
There are three main types of directives:
1) page - processing information for this page.
2) Include - files to be included.
3) Tag library - tag library to be used in this page.
Directives do not produce any visible output when the page is requested but change the way the JSP Engine processes the page.
For example,you can make session data unavailable to a page by setting a page directive (session) to false.
1. Page directive
This directive has 11 optional attributes that provide the JSP Engine with special processing information. The following table lists the 11 different attributes with a brief description:
language
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Which language the file uses.
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<%@ page language = "java" %>
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extends
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Superclass used by the JSP engine for the translated Servlet.
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<%@ page extends = "com.taglib... %>
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import
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Import all the classes in a java package into the current JSP page. This allows the JSP page to use other java classes.
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<%@ page import = "java.util.*" %>
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session
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Does the page make use of sessions. By default all JSP pages have session data available. There are performance benefits to switching session to false.
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Default is set to true.
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buffer
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Controls the use of buffered output for a JSP page. Default is 8kb
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<%@ page buffer = "none" %>
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autoFlush
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Flush output buffer when full.
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<%@ page autoFlush = "true" %>
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isThreadSafe
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Can the generated Servlet deal with multiple requests? If true a new thread is started so requests are handled simultaneously.
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info
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Developer uses info attribute to add information/document for a page. Typically used to add author,version,copyright and date info.
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<%@ page info = "visualbuilder.com test page,copyright 2001. " %>
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errorPage
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Different page to deal with errors. Must be URL to error page.
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<%@ page errorPage = "/error/error.jsp" %>
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IsErrorPage
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This flag is set to true to make a JSP page a special Error Page. This page has access to the implicit object exception (see later).
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contentType
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Set the mime type and character set of the JSP.
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2. Include directive
Allows a JSP developer to include contents of a file inside another. Typically include files are used for navigation,tables,headers and footers that are common to multiple pages.
Two examples of using include files:
This includes the html from privacy.html found in the include directory into the current jsp page.
<%@ include file = "include/privacy.html" %>
or to include a naviagation menu (jsp file) found in the current directory.
<%@ include file = "navigation.jsp" %>
Include files are discussed in more detail in the later sections of this tutorial.
3. Tag Lib directive
A tag lib is a collection of custom tags that can be used by the page.
<%@ taglib uri = "tag library URI" prefix = "tag Prefix" %>
Custom tags were introduced in JSP 1.1 and allow JSP developers to hide complex server side code from web designers.
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