Directive Elements in JSP

Introduction to Directive Elements

Directives control the processing of JSP page. Directive tag instructs the web container at the time of translating a JSP page into corresponding Servlet page.

There are 3 types of directives in JSP:
i. page directive
ii. include directive
iii. taglib directive

Syntax of Directive:
<%@ directive attribute= "value" %>

page directive

The page directive allows applying different attributes to be added in JSP.  These attributes give special processing information to the JSP container.

Following are the page directive attribute:

Attribute	Description
import	Import list of packages, classes an interfaces in servlet class definition. Example: <%@ page import = "java.util.Date" %>
extends	Used to extend the parent class that will be generated by Servlet. Example: <%@ page extends = "mypackage.DemoClass"%>
language	Defines which scripting language to be used in the page. Example: <%@ page language = "value"%>
session	Specifies the JSP page participating in an HTTP session. Example: <%@ page session = "true"%>
buffer	Specifies a buffer model to handle output stream generated by JSP page. Example: <%@ page buffer = "4kb"%>
autoFlush	Specifies that buffer should be flushed automatically. The default value of autoFlush attribute is ‘true’. Example: <%@ page autoFlush = "false"%>
info	Sets the information of the JSP page which is retrieved later by using getServletInfo( ) method. Example: <%@ page info = "Given by Surendra Maurya"%>
contentType	Sets the content of the JSP page. Example: <%@ page contentType="text/html"%>
isThreadSafe	It is used to define the threading model for the JSP page which is generated by Servlet because JSP and servlet both are thread safe. Example: <%@ page isThreadSafe="false"%>
errorPage	Define the error page, if any error generates in current page, it will be redirected to the error page. Example: <%@ page errorPage="erroropage.jsp"%>
isErrorPage	Defines whether the current JSP page is error page or not. Example: <%@ page isErrorPage="true" %>
isELIgnored	Specifies whether the expression will be evaluated or not in JSP page. Example: <%@ page isELIngored="true" %>

include directive

• The include directive is used to insert a file like JSP file, html file or text file. It will parse the JSP elements during translation phase.
• The main advantage of the include directive is code reusability functionality.

Syntax:
<%@ include file="resourceName" %>

taglib directive

• It is used to define a tag library that contains many custom tags. JSP technology supports the development of reusable components called custom actions.
• The custom tags can be customized through passing the attribute from invoking page. It can be accessed by all the available objects of JSP page.

Syntax:
<%@ taglib prefix="prefixOfTag" uri="uriOfTagLibrary" %>