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Sunday, May 31, 2009

INTRODUCTION TO JSP TAGS

In this lesson we will learn about the various tags available in JSP with suitable examples. In JSP tags can be devided into 4 different types. These are:


1. Directives
In the directives we can import packages, define error handling pages or the session information of the JSP page.

2. Declarations
This tag is used for defining the functions and variables to be used in the JSP.

3. Scriplets
In this tag we can insert any amount of valid java code and these codes are placed in _jspService method by the JSP engine.

4. Expressions
We can use this tag to output any data on the generated page. These data are automatically converted to string and printed on the output stream.


Now we will examine each tags in details with examples. DIRECTIVES

Syntax of JSP directives is:

<%@directive attribute="value" %>

Where directive may be:

1. page: page is used to provide the information about it.
Example: <%@page language="java" %>

2. include: include is used to include a file in the JSP page.
Example: <%@ include file="/header.jsp" %>

3. taglib: taglib is used to use the custom tags in the JSP pages (custom tags allows us to defined our own tags).
Example:<%@ taglib uri="tlds/taglib.tld" prefix="mytag" %>


and attribute may be:

1. language="java"
This tells the server that the page is using the java language. Current JSP specification supports only java language.
Example: <%@page language="java" %>

2. extends="mypackage.myclass"
This attribute is used when we want to extend any class. We can use comma(,) to import more than one packages.
Example:<%@page language="java" import="java.sql.*,mypackage.myclass" %>

3. session="true"
When this value is true session data is available to the JSP page otherwise not. By default this value is true.
Example: <%@page language="java" session="true" %>

4. errorPage="error.jsp"
errorPage is used to handle the un-handled exceptions in the page.
Example: <%@page language="java" session="true" errorPage="error.jsp" %>

5. contentType="text/html;charset=ISO-8859-1"
Use this attribute to set the mime type and character set of the JSP.
Example: <%@page language="java" session="true" contentType="text/html;charset=ISO-8859-1" %>
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