Jsp Directive Elements

• A jsp directive is a translation time instruction to the jsp engine.
• we have three kinds of directives.

1. Page directive
2. Include directive
3. Taglib directive

Page Directive:

• Page directive is one of the three translation time instructions to the jsp engine.
• Page directive has 13 attributes.
• Mostly page directive used to import java packages in to jsps
  <% @ page import="java.sql.*, java.util,*"%>

Jsp Page directive attributes:

1. import
2. session
3. isErrorPage
4. errorPage
5. ContentType
6. isThreadSafe
7. extends
8. info
9. language
10. autoflush
11. buffer

import:

This attribute defines the list of packages,each separated by comma.

Syntax:

import="package.class"

Example:

<%@page import="java.util.*,java.io.*"%>

Session:

The session attribute indicates that  whether or not the JSP page uses HTTP sessions. If it is tree means that the JSP page has access to a
existing session object and it is false means that the JSP page cannot access the built-in session object.

Syntax:

session="true|false"

Example:

<%@ page session="true"%>

isErrorPage:

In JSp Page IsErrorPage indicates that whether or not the current page can act as a error page or not.If it is true it is Supposed to handle the Errors..

Syntax:

isErrorPage="true|false"

Example:

<%@ page isErrorPage="false"%>

errorPage:

The errorPage attribute tells the JSP engine which page to display if there is an error while the current page runs.

The value of the errorPage attribute is a relative URL.
The following directive displays MyErrorPage.jsp when all uncaught exceptions are thrown

Syntax:

errorPage="url"

Example:

<%@ page errorPage="error.jsp"%>

contentType :

The contentType attribute defines the MIME(Multipurpose Internet Mail Extension) type of the HTTP response.

Syntax:

contentType="MIME-Type"

Example:

<%@ page contentType="text/html; charset=ISO-8859-1"%>

isThreadSafe:

isThreadSafe option tells that a page as being thread-safe. By default, all JSPs are considered thread-safe.
If you set the isThreadSafe is false, the JSP engine makes sure that only one thread at a time is executing your JSP.

Syntax:

isThreadSafe="true|false"

Example:

<%@ page isThreadSafe="true"%>

extends:

Indicates the superclass of servlet when jsp translated in servlet.

Syntax:

extends="package.class"

Example:

<%@ page extends="com.Connect"%>

info:

This attribute simply sets the information of the JSP page which is retrieved later by using getServletInfo() method of Servlet interface.

Syntax:

info="message"

Example:

<%@ page info="created by instanceofjava" %>

language:

language tells the server about the language to be used in the JSP file.
Presently the only valid value for this attribute is java.

Syntax:

language="java"

Example:

<%@ page language="java"%>

autoflush:

autoflush attribute true indicates that the buffer should be flushed when it is full and false indicates that an exception should be thrown
when the buffer overflows.

Syntax:

autoflush="true|false"

Example:

<%@ page autoFlush="true"%>

Buffer:

The buffer attribute sets the buffer size in kilobytes to handle output generated by the JSP page.The default size of the buffer is 8Kb.

Syntax:

buffer="sizekb|none"

Example:

<%@ page buffer="8kb"%>

include Directive:

The include directive is used to include the contents of any resource it may be jsp file, html file or text file.

It allows a JSP developer to include source code of a file inside jsp file at the specified place at a translation time.

Advantage of Include directive:

Code Reusability

Syntax:

<%@ include file="sourceName"%>

Example:

<%@ include file="/foldername/fileName"%>

taglib Directive:

The taglib directive makes custom actions available in current page through the use of tag library.
TLD (Tag Library Descriptor) is used for file to define the tags.

Syntax:

<%@ taglib uri="path" prefix="prefix"%>

Example:

<%@ taglib uri="http://www.instanceofjava/tags" prefix="mytag"%>