Introduction:
A custom tag is a user-defined JSP language
element. If a JSP page containing a custom tag that is translated into a
servlet first,and then the tag is converted to operations on a tag handler
class. The web container then invokes these operations at the time of JSP
page’s servlet is executed.
Steps to create a custom tag:
- Create a tag
handler file. This file contains the tag handler class that will be
executed when the JSP processor encounters your custom tag on a JSP page.
- Create a tag
library descriptor (TLD) file. The tag library descriptor file is an XML
file that tells the JSP processor where to find the tag handler class once
it encounters your custom tag on a JSP page.
- We have to
include the taglibrary directive in jsp page.
- Include the
following specifications in web.xml to make your custom tags available in
a JSP's Page.
<taglib> = Root tag.
<taglib-uri> = uri identifying a
Tag Library.
<taglib-location> = location, as a resource, where
the TLD file
can be found.
Types of Custom Tags
- Empty tags:
Refer to the custom tags that do not have any attribute or body. The following
code snippet shows an empty custom tag:
<td:welcome />
- Tags with attributes:
Refer to custom tags for which you can define attributes to customize the
behavior of the custom tag. The following code snippet shows a custom tag
with an attribute color:
<td: welcome
color=”blue”></td:welcome>
- Tags with a
body: Refer to the custom tag within which you can define nested custom tags,
scripting elements, actions, HTML text,
and JSP directives. The following code snippet shows a custom tag
that contains a JSP scripting element as its body:
<td: welcome>
The
Current Date is : <%=today_date%>
</td:welcome>
Sample
Code
Tag Handler Classes (defines
behavior of the tag)
CurrentDate.java
/**
*
Created on : Jan 29, 2013, 12:26:45 PM
*
@author Hariharan Selvarajan
*
This the tag handler class for custom Empty Tag.
*/
package
com.customtags;
import
java.util.Calendar;
import
javax.servlet.jsp.JspWriter;
import
javax.servlet.jsp.tagext.TagSupport;
public
class CurrentDate extends TagSupport
{
/**
* This is an example class for */
@Override
public int doStartTag()
{
try
{
JspWriter out =
pageContext.getOut();
Calendar now =
Calendar.getInstance();
//Get the current date.
out.println("<center><table><tr><td>"+
Calendar.getInstance().get(Calendar.DATE)+"/"+
(Calendar.getInstance().get(Calendar.MONTH)+1)+"/"+
Calendar.getInstance().get(Calendar.YEAR)+
"</td></tr></table></center>");
}
catch (Exception e)
{
System.out.println("Exception
in Custom Tags");
}
return (SKIP_BODY);
}
@Override
public int doEndTag()
{
return EVAL_PAGE;
}
}
Tag_Attribute.java
/**
*
Created on : Jan 29, 2013, 12:50:18 PM
* @author Hariharan
* This
the tag handler class for custom tag with attributes type.
*/
package
com.customtags;
import
javax.servlet.jsp.JspWriter;
import
javax.servlet.jsp.tagext.*;
public
class Tag_Attribute extends TagSupport
{
//Variables corresponding to attributes.
private String bgcolor;
private String color;
private String name;
private String width;
public String getBgcolor()
{
return bgcolor;
}
public void setBgcolor(String bgcolor)
{
this.bgcolor = bgcolor;
}
public String getColor()
{
return color;
}
public void setColor(String color)
{
this.color = color;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
public String getWidth()
{
return width;
}
public void setWidth(String width)
{
this.width = width;
}
//Welcome Notification.
@Override
public int doStartTag()
{
JspWriter out = pageContext.getOut();
String align="center";
final int BORDER_STYLE =1;
try
{
out.println("<center><table
border="+BORDER_STYLE+"
bgcolor="+bgcolor+">");
out.println("<tr><td
width="+300+" align="+align+"
width="+70+"><font
color="+color+"> Welcome to "+
getName()+"</font>"+"</td></tr><table></center>");
}
catch (Exception ex)
{
System.out.println("Custom tag
with attribute has error");
}
return (SKIP_BODY);
}
}
Tag_Body.java
/**
* Created on : Jan 29, 2013, 01:27:46 PM
* @author Hariharan Selvarajan
*
* This the tag handler class for custom tag with
body type.
* Display the elements of collection in HTML table
format.
*/
package
com.customtags;
import
java.util.Collection;
import
java.util.Iterator;
import
javax.servlet.http.HttpSession;
import
javax.servlet.jsp.tagext.BodyTagSupport;
public
class Tag_Body extends BodyTagSupport
{
//Variables corresponding to attributes.
private Iterator iterator;
private Collection collection;
public Collection getCollection()
{
return collection;
}
public void setCollection(Collection
collection)
{
this.collection = collection;
}
@Override
public int doStartTag()
{
if (getCollection() == null)
{
System.out.println("No
collection with name "
+ getCollection()
+ " found");
}
iterator = getCollection().iterator();
if (iterator.hasNext())
{
pageContext.setAttribute("item", iterator.next());
return EVAL_BODY_INCLUDE;
}
else
{
return SKIP_BODY;
}
}
//called after the body content is
evaluated
@Override
public int doAfterBody()
{
{
if (iterator.hasNext())
{
pageContext.setAttribute("item", iterator.next());
return EVAL_BODY_AGAIN;
}
else
{
return SKIP_BODY;
}
}
}
}
Tag
Library Descriptor
customtag.tld
<?xml
version="1.0" encoding="UTF-8"?>
<!DOCTYPE
taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library
1.2//EN" "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>taglib-none</short-name>
<uri>/WEB-INF/tlds/customtag</uri>
<tag>
<name>currentDate</name>
<tag-class>com.customtags.CurrentDate</tag-class>
<body-content>EMPTY</body-content>
</tag>
<tag>
<name>tag_Attribute</name>
<tag-class>com.customtags.Tag_Attribute</tag-class>
<body-content>EMPTY</body-content>
<attribute>
<name>bgcolor</name>
<required>true</required>
<!-- bgcolor is required -->
</attribute>
<attribute>
<name>width</name>
</attribute>
<attribute>
<name>color</name>
<required>false</required>
<!-- color is required -->
</attribute>
<attribute>
<name>name</name>
<required>true</required>
<!-- name is required -->
</attribute>
</tag>
<tag>
<name>tag_Body</name>
<tag-class>com.customtags.Tag_Body</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>collection</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<!-- collection is required -->
</attribute>
</tag>
</taglib>
customtags.jsp (Here we are
going to use the custom tag)
<%--
Created on : Jan 29, 2013, 02:16:37 PM
Author
: Hariharan Selvarajan
Description: Custom Tags Creation
--%>
<!DOCTYPE
HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<%@page
import="javax.servlet.jsp.PageContext"contentType="text/html"
pageEncoding="UTF-8"%>
<%@taglib
uri="/WEB-INF/tlds/taglib-none.tld" prefix="taglib"%>
<html>
<head>
<meta
http-equiv="Content-Type"content="text/html;charset=UTF-8">
<title>Page</title>
</head>
<body>
<h1>
<p align="right">
<taglib:currentDate/> </p>
</h1>
<br/> <br/>
<taglib:tag_Attribute
name="Custom Tag Demo" width="300" bgcolor="BROWN"
color="White"/>
<br/> <br/>
<%
java.util.Vector vector =
new java.util.Vector();
vector.addElement("Prakash");
vector.addElement("Uvaraj");
vector.addElement("Selvam");
vector.addElement("Ragaven");
vector.addElement("Kannan");
%>
<table border="1">
<taglib:tag_Body
collection="<%=vector%>">
<tr>
<td
align="center">Welcome Mr.
<%=pageContext.getAttribute("item")%></td>
</tr>
</taglib:tag_Body>
</table>
<taglib:forwardAction action="index.jsp"/>
</body>
</html>
Web.xml
<?xml
version="1.0" encoding="UTF-8"?>
<web-app
version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<session-config>
<session-timeout>
30
</session-timeout>
</session-config>
<taglib>
<taglib-uri>/taglib-none.tld</taglib-uri>
<taglib-location>/WEB-INF/tlds/customtag.tld</taglib-location>
</taglib>
<welcome-file-list>
<welcome-file>customtags.jsp</welcome-file>
</welcome-file-list>
</web-app>
OUTPUT
