Jsp Drectives tutorial

 

How to use  directives in JSP

 III. Jsp Drectives

e-training-directives-tutorial
 

 JSPHome

What are Directives in JSP?

 

Directives in JSP Page, are nothing but elements of JSP code, which directs web container at the time of converting, JSP page to servlet. 

Directive provides special information, messages about the entire JSP page which is used in processing of the page. This information is global. 


There are three types of directive tags available in JSP.

 


  • page 
  • include 
  • taglib 

All directives start with @ symbol.

<%@   %>  → directives used to import library files.

Page directive

example:
 
 <%@ page import="javal.util.*;" %>

include directive

 

   It includes files like html,jsp,xml  at compile time to this page. 

	<%@ include file="relativeurl" %>
	<%@ include file="header.html" %>
 
example:

pageIndludedemo.jsp
---------------

<%@ page pageEncoding="UTF-8" %>
<%@ include file="PageDemo.jsp" %>

<%    out.println("Including Page"); %> 

o/p: pageDemo o/p plus current page data.


taglib directive:

  
<%@ taglib uri=taglibraryUri" prefix="tagprefix" %>

<%@ taglib uri="mytags" prefix="mt" %>

pagedemo.jsp 
ex:

<%@ page import="java.util.*" %>
 
<b><%Date d = new Date();
    out.println(d);
%></b>

page directive attributes 


import : To import java packages.

extends: Extends only HttpServlet/subclasses.

isErrorpage(boolean value): Tells the page wether errorpage/not.
	    ex: <%@ page iserrpage=true %>

isThhreadsafe: makes the JSP page singlethreadmodel.
	    ex: <%@ page isthreadsafe=true %>

buffer: Used to set buffer size of response obj, and is used in file downloading application.
	   ex: <%@ page buffer=8192 bytes %>   (8kb)
	   can be 16 and 32 kb.


errorpage: if there are any exception in cur jsp page insteading of 
           displaying stacktrace errorpage is displayed
	   ex: <%@ page errorpage="error.html" %> 

pageencoding: used to specify page encoding
	   <%@ page pageEncoding="ISO-8859-1" %>

session:by using session attribute you can avoid creating session obj by 
           saying session=false
	   ex: <% @page session=true %>

autoflush:used clears buffer of responseobj automatically
	   ex: <% @page autoflush=true %>

contenttype:diff content types text/plain or text/html, text/xml

	   ex: <% @page contenttype="text/html" %>

errorpage.jsp 
 
 URL Looks as shown..
 
 .../errorpage.jsp?name=xxx

 
errorpage.jsp
-------------

<%@ page errorpage="error.html" %> 
    String user= req.getParameter("name");
    out.println("Hello.."+user);
%>

ex2:
<%@ page errorPage="err.jsp" %>
<html>
     <body>
       <%
	     int i = 10;
	     i = i / 0;
       %>
    </body>
</html> 
 
 
 
err.jsp

<%@ page isErrorPage = "true"%>
<%@ page import = "java.io.*" %>

<HTML>
    <HEAD>
        <TITLE> Coding-zon demo - JSP custom error page </TITLE>
    </head>
    <body>
       <h2>Application has generated an error</h2>
       <h3>Please check for the error given below</h3>
       <b>Exception:</b><br>
       <font color="red"><%= exception.toString() %></font>
    </body>
</html>


Javabean feautres:

  • Java Bean is a simple java class.
  • It contains private properties(member variables) and get/set methods for each property. 
  • It implements serializable.

 

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