This document provides an overview of implementing JSP tag extensions in Java. It discusses: 1. Custom tags which allow creating reusable tags to reduce scripting elements in JSP pages. Tag libraries define custom tags and major features include reusability, readability, maintainability, and portability. 2. Elements of tag extensions including the TLD file which documents the tag library, the tag handler Java class which implements tag functionality, and the taglib directive which identifies the tag library location. 3. Interfaces for developing tag handlers like Tag, IterationTag, BodyTag, and SimpleTag and classes that provide default implementations like TagSupport, BodyTagSupport, and SimpleTagSupport.

1. {
Implementing JSP
Tag Extensions

2. CUSTOM TAGS
 User Defined tags
 Reduce the use of scripting elements
in a JSP page
 Allows to create new and reusable tags
 Can use in any JSP page with the help
of tag libraries

3.  A Tag library provides the capability to
define new customized tags
 Major features of custom tags:
 Reusability
 Readability
 Maintainability
 Portabiltity
Exploring the Elements of Tag
Extensions

4.  The TLD file
 The tag handler
 The taglib directive
Basic elements of Custom tags

5.  XML document describing tag library
 Provides documentation of tag library and
version information of JSP container
 Contains the name of TagLibraryValidator
class
The TLD file

6.  Used to implement the functionality of a custom
tag
 To set a custom tag in a JSP page,
<%@ taglib prefix=“p” uri=“Mytld.tld” %>
 Features:
 Declares that a tag library is used
 Identifies the location of the tag library
 Associates a tag prefix with the usage of
actions in the library
The taglib directive

7.  Java class where a custom tag is defined
 Can define tag handlers by implementing interfaces
or by extending an abstract base class from
javax.servlet.jsp.tagext package
 Various tag handler interfaces are Tag, BodyTag,
IterationTag and SimpleTag
 JSP technology defines 2 types of tag handlers:
 Classic tag handler
 Simple tag handler
The Tag handler

8. Exploring the Tag Extension API
 The tag extension API provides the
javax.servlet.jsp.tagext package.
 Contains various classes and interfaces
 Similar to HTML/XML tags

9. Terms associated with the
implementation of a tag extension
 Tag name-combination of prefix and suffix,separated
by a colon.
For example :-
<jsp:forward />tag
 Attributes-refers to a value that is assigned to an
attribute of a tag.

10.  Nesting-process in which a tag is used within
another.
 For example, <jsp:param />tag is used within
<jsp:include /> and <jsp:forward />tags
 Body content-refers to content,such as expressions
and scriplets.

11. The tag Extension Interfaces
§ The Tag interface
§ The JspTag interface
§ The IterationTag interface
§ The BodyTag interface
§ The DynamicAttributes interface
§ The SimpleTag interface
§ The TryCatchFinally interface
§ The JspIdConsumer interface

12. 1. The Tag interface
Basic protocol between tag handler and a JSP
page.
 dostartTag() and doEndTag()
 setParent(tag t)
 getParent()
 release()

13. Describing the Fields of the Tag
interfaces
 EVAL_BODY_INCLUDE
 EVAL_PAGE
 SKIP_BODY
 SKIP_PAGE

14. 2. The JspTag Interface
 Serves as a base interface for the Tag and
SimpleTag interface.
 Used for organizational and type-safety purposes.
 BodyTag,IterationTag,SimpleTag and Tag -
interfaces are sub-interfaces.

15. 3. The IterationTag interface
 Build tag handlers that repeatedly re-evaluate the body of a
custom tag.
 Extends the Tag interface.
 Method:
 doAfterBody()
 Fields:
 EVAL_BODY_AGAIN-Re-evaluates the body content.
 SKIP_BODY-stops the evaluation of the body content.

16. 4. The BodyTag Interface
 Extends the Iteration Tag interface.
 Methods:
doInitBody() - evaluates the body of a custom tag
before initializing it,not invoked for empty tag.
setBodyContent(BodyContent b)-sets the body
content of the custom tag.

17. 5. The DynamicAttributes interface
 To provide support for dynamic attributes.
 SetDynamicAttribute() avoids the translation-
time errors.
 JspException exception is thrown.

18. 6. The simpleTag Interface
 Created by implementing the SimpleTag interface.
 Methods:
 doTag() - evaluating and iterating the body content
of a tag.
 getParent() - returns the parent of the custom tag.
 setJspBody - provides the body of the custom tag as
a JspFragment object.

19. 7. The TryCatchFinally Interface
 To handle the exceptions that may occur within the tag
handler class.
 doStartTag() and doEndTag() may throw JspException.
 Methods:
doCatch()-invoked whenever there an exception arises
during the evaluation of the body of the current tag.
doFinally()-gets invoked after the processing of the
doEndTag() method is complete.

20. 8. The JspIdConsumer Interface
 Jsp container should provide a compiler generated id .
 JspId attribute is a string value,similar to <jsp:id>tag
 Difference is <jsp:id> is evaluated at the execution time.
 provides single method,setJspId(string id)
 Unique id during translation process.

21. The Tag Extension Classes
The TagSupport Class
 Is an abstract class that implements the tag as well as
IterationTag interfaces and provides support for all
the methods.
 Static method
 Methods:
 doAfterBody()-body content of the tag after the
invocation of the doStartTag()

22.  doEndTag()-returns EVAL_PAGE field,by default,on
executing the end tag.
 doStartTag()-SKIP_BODY field after the execution of the
start tag.
 getValue()- returnsng string value.
 getId()-returns values of the id attribute/null value
 getValues()-get the corresponding values

23.  removeValue(java.lang.string k)-removes the string
value.
 setId(java.lang.string Id)-Sets the id attribute.
 setPageContext()-Sets the page context.
 Fields
 Id-specifies a String value for a tag
 PageContext-provides access to al the namespaces and
page attributes.

24. The BodyContent Class
 Is a subclass of the JspWriter class and encapsulates
the evaluation of the body of an action.
 pushBody() or popBody()-creates instances of the
BodyContent class

25.  Methods:
 getReader()-Returns the value of the BodyContent object
as a Reader object.
 getString()-as a string
 writeOut(java.io.Writer out)-writes the content of the
BodyContent object into a writer object.
 getEnclosingWriter()-enclosing JspWriter object.
 clearBody()-clrs the body of the buffer.

26. The BodyTagSupport Class
 Implements the BodyTag interface .
 Acts as a base class to create tag handlers without
defining each method of the BodyTag interface

27. 8.11

28. The FunctionInfo Class
 Provides information abt a function defined in the tag
library.
 Instantiated from the TLD file.
 Available only at the time of translation of a JSP
page.

29.  Methods
 getFunctionClass() - Returns the class of a function.
 getFunctionSignature() - signature.
 getName - Name

30. The JspFragment class
 Encapsulates the jsp code in an object that can be
invoked multiple times.
 Manually either by page author or by TLD file.
 Methods:
 getJspContext()-returns the JspContext object that is used
by the current JspFragment object.
 Invoke(java.io.Writer out)-Executes the JspFragment
object.

31. The SimpleTagSupport Class
 Implements the SimpleTag interface
 Provides the defination for all the implemented
methods of the SimpleTag interface.
 Methods:
 doTag() -processes a simple tag handler.
 getJspBody() -returns a fragment that encapsulates the
body passed by the container.

32.  getJspContext()-returns the page context.
 getParent()-parent tag of a simple tag.
 setJspBody(JspFragment jspBody)-stores the specified
JspFragment object.
 setJspContext(JspContext pc)-stores the provided JSP
context in the private JspContext.
 setParent(JspTag parent)-sets the parent tag of the simple
tag.

33. The TagAdapter class
 Allows the collaboration bw classic tag handlers and
simple tag handlers.
 Methods:
 getAdaptee()-instance of simple tag handler that is
being adapted to the tag interface.
 getParent()-returns the parent of the simple tag.

34. The TaglibraryInfo class
 Provides translation-time information associated
with a taglib directive and TLD.

35. 8.16

36. 8.17

37. The TagInfo Class
 Provides information of a specific tag provided in a
tag library.
 Instance of TLD.

38. 8.18

39. 8.19

40. The TagFileInfo Class
 Provides information about a tag file in a tag library.
 TLD instantiates,available only at translation time.
 Code Snippet
 TagFileInfo(name, path, Taginfo)

41.  Methods:
 getName()-returns a unique action name of the tag.
 getPath()-path to locate the .tagfile.
 getTagInfo()object containing the information abt the tag.

42. The TagAttributeInfo Class
 Contains information abt tag attributes.
 ID as its attribute.
 Specifies a string value for a custom tag.

44. The TagExtraInfo Class
 Provides a mechanism to validate custom tags using tag
attributes in TLD.
 The <attribute>tag contains a set of three tags,
name> ,<required> and<rtexprvalue>
 Low level validation mechanism.

45.  Methods:
 getTagInfo()-returns TagInfo object of the custom tag.
 getVariableInfo(Tagdata data)-a zero length array,if no
scripting variables are defined.
 isValid(Tagdata data)-instance is valid.
 setTagInfo(Taginfo tagInfo)-sets the specied TagInfo
for the custom tag handler.

46. The PageData Class
 Provides the translation-time information on a JSP
page.
 Provides a single method i,e getInputStream().
 Returns an input stream of a JSP page in the form of
XML and stream encoding is done in UTF-8

47. The VariableInfo Class
 Determines the type of the scripting variables that are
created or modified by a tag at runtime
 Class should be provided in the classpath of the web
application.

48. The TagData Class
 Object of TD is used as an argument in the Validate(),
isValid(),getVariableInfo() methods of the TagExtraInfo
class at the translation time.

49. The TagLibraryValidator Class
 Validates a JSP page during the translation time.
 Validate(String prefix,String uri,PageData page)
 First two parameters are used to indicate how a tag
library is mapped in the jsp page.
 Last parameter is used to represent the XML view of the
page being validated.

50. The ValidationMessage Class
 Is a piece of information that is provided by either the
TagLibraryValidator or the TagExtraInfo object.
 JSP container can also use this VM obj to retrieve
information abt the location of errors.
 Methods:
 getId()-returns <jsp:id> attribute.
 getMessage()-localized validation message.

51.  Java class that implements the Tag, IterationTag
or BodyTag interface
Working with Classic Tag
Handlers

52.  Steps to develop the ClassicTag application:
 Creating the Tag handler for ClassicTag
application
 Creating TLD for ClassicTag application
 Creating html file for ClassicTag application
 Creating JSP file for ClassicTag application
 Configuring web.xml file for ClassicTag
application
 Defining the directory structure of ClassicTag
application
 Packaging, running and deploying the
ClassicTag application
Implementing Classic Tags

53. CustomMessage.java
package com.kogent.tags;
import javax.servlet.ServletRequest;
import javax.servlet.jsp.tagext.*;
public class CustomMessage extends BodyTagSupport
{
String pname;
private static final long serialVersionUID = 1L;
public void setParamName(String s)
{
pname=s;
}

54. public String getParamName()
{
return pname;
}
public int doStartTag()
{
ServletRequest req=pageContext.getRequest();
String pvalue=req.getParameter(pname);
if ((pvalue.equals("japan")) || (pvalue.equals("Japan")))
{
return EVAL_BODY_INCLUDE;
}

55. else
{
return SKIP_BODY;
}
} //doStartTag//doStartTag
public int doAfterBody()
{
return SKIP_BODY;
}//doAfterBody
public int doEndTag()
{
return EVAL_PAGE;
}//doEndTag
}

56. CustomTags.tld
<?xml version="1.0" ?>
<jsp-version>2.1</jsp-version>
<tlib-version>1.1</tlib-version>
<short-name>tag</short-name>
<tag>
<name>check</name>
<tag-class>com.kogent.tags.CustomMessage</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>check</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
</taglib>

57. <html>
<body>
<form action="TestPage.jsp">
<b> PREDICT AND WIN !!! </b>
<BR/>
<BR/>
<p style="color:blue">The country which is known as "land of rising
sun" </p>
<input type="text" name="opt"/>
<input type="submit" value="check"/>
</form>
</body>
</html>
Home.html

58. <%@taglib uri="/WEB-INF/CustomTags.tld" prefix="tag"%>
<html>
<body>
<tag:check paramName = "opt">
<b>congratulations you have won a prize!!!</b>
</tag:check>
</body>
</html>
TestPage.jsp

59. <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID" version="3.0">
<welcome-file-list>
<welcome-file>home.html</welcome-file>
</welcome-file-list>
</web-app>
Web.xml

60. Displaying the Directory structure of Classic tag application

61. Output

62.  Java class that implements the SimpleTag interface
 The javax.servlet.jsp.tagext.SimpleTagSupport class
provides default implementation of all methods in
simple tags
Working with Simple Tag
Handlers

63.  Steps to develop the SimpleTag application:
 Creating the Tag handler for SimpleTag application
 Creating TLD for SimpleTag application
 Creating JSP file for SimpleTag application
 Configuring web.xml file for SimpleTag application
 Defining the directory structure of SimpleTag
application
 Packaging, running and deploying the SimpleTag
application
Implementing Simple Tags

64. package com.kogen.tags;
import javax.servlet.jsp.tagext.*;
import javax.servlet.jsp.*;
import java.io.*;
import java.util.Date;
public class CustomMessage1 extends SimpleTagSupport
{
public void doTag() throws JspException,IOException {
JspContext context=getJspContext();
JspWriter Out=context.getOut();
Out.println("Welcome!!! You are visting this Web page on"+new
Date());
}
}
CustomMessage1.java

65. <?xml version="1.0" ?>
<taglib version="2.1" 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/web-
jsptaglibrary_2_ 1.xsd">
<jsp-version>2.1</jsp-version>
<tlib-version>1.1</tlib-version>
<short-name>tag</short-name>
<tag>
<name>CustomMessage1</name>
<tag-class>com.kogent.tags.CustomMessage1</tag-class>
<body-content>empty</body-content>
</tag>
</taglib>
CustomTags.tld

66. <%@ taglib uri="/WEB-INF/CustomTags.tld" prefix="tag"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<link rel="stylesheet" type="text/css" href="mystyle.css">
</head>
<body>
<tag:CustomMessage1/><br>
</body>
</html>
test.jsp

67. <?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
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_3_0.xsd">
<welcome-file-list>
<welcome-file>test.jsp</welcome-file>
</welcome-file-list>
</web-app>
Web.xml

68. Displaying the Directory structure of Simple tag application

69. Output:

70. 1. What are the major features of custom tags?
2. What are the 3 basic elements of custom tags?
3. What is TLD file?
4. Tell me any 1 feature of taglib directive.
………..?

71. Thank you