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®
IBM Software Group
JSP Custom Tags
© 2007 IBM Corporation
4.1.0.3
Unit objectives
After completing this unit, you should be able to:
Describe the advantages of using JSP custom tags
List the major steps in developing and using JSP custom tags
Develop basic tag handler classes to implement JSP custom
tags
Create and modify taglib descriptor files
Package JSP taglib implementation classes and taglib
descriptor files
Understand the uses of the JSTL
Name some of the tags included in the JSTL and their
purposes
2
JSP Custom Tags Overview
Nine standard actions must be provided by any compliant JSP
implementation:
useBean, setProperty, getProperty
include, forward
plug-in, params, param, fallback
Custom tags allow developers to create additional actions
beyond the standard set
Custom actions are invoked via custom tags in a JSP page
Tag libraries are collections of custom tags
Support for JSP custom tags is required by the JSP
specification
<jsp:useBean id="customer" class="com.ibm.model.customer" />
<jsp:setProperty name="customer" property="id" value="0" />
<jsp:include page=“banner.jsp” />
3
Why Use JSP Custom Tags?
Role-based development
Model classes (business objects and data storage layers)
are developed by Java and EJB developers
Controller classes (servlets) are developed by Java
developers
View-based JSP pages are developed by HTML developers
Different roles:
Use different tools
Have different skills
Best Practice
MVC design is well established
Use the right tools for the right jobs
4
Steps to Create and Use a Custom Tag Library
To develop a tag, you need to:
Design your tags and attributes
Declare the tag in a tag library descriptor (TLD)
Develop a tag handler class
Develop helper classes for the tag (if needed)
To use a custom tag, the JSP needs to:
Include the tag library using the taglib directive
Code the custom tag with any needed attributes
Test your tags
class 1
JSP
Page
TLD
class 2
5
helper
class
Tag Usage Example
<!DOCTYPE HTML PUBLIC
"-//W3C//DTD HTML 4.01 transitional//EN">
<HTML><HEAD>
<%@ taglib uri="/WEB-INF/tld/taglib.tld" prefix=“tl"
%>
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1“
%>
<TITLE>Date Demo</TITLE>
</HEAD>
<BODY>
<h1>Date Demo</h1>
<P>Fully formatted date:
<tl:date format=”full”/>
</P>
</BODY></HTML>
6
JSP Page Without Custom Tags
<!DOCTYPE HTML PUBLIC
"-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML><HEAD>
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<TITLE>Date Demo</TITLE>
</HEAD><BODY>
<h1>Date Demo</h1>
<P>Fully formatted date:
<% java.util.Locale locale =
pageContext.getRequest().getLocale();
java.text.DateFormat fmt =
java.text.DateFormat.getDateInstance
(java.text.DateFormat.FULL,locale);
String date = fmt.format(new java.util.Date()); %>
<%= date %>
</P>
</BODY></HTML>
7
Using Custom Tags with Application Developer
Page Designer has different ways of selecting a tag for
inclusion with JSP
1. Select JSP->Insert Custom
2. Drag Custom from JSP Tags drawer in Palette
Select desired tag from Insert Custom Tag dialog
1
8
2
JSP Standard Tag Library (JSTL)
Encapsulates as tags core functionality of many Web applications
Supports tasks such as:
Flow (iteration and conditionals)
Manipulation of XML documents
Internationalization tags
SQL tags
J2EE 1.4 includes both JSP and JSTL
JSTL taglibs included with Rational Application Developer
9
Sample JSTL Tags
Set a variable in a specific scope to a value
<c:set var="name" scope="scope" value="expression"/>
Display a value, or an alternative if the first value is null
<c:out value="expr" default="expr" escapeXml="boolean"/>
Example:
Hello <c:out value="${user.name}" default="Guest"/>!
Conditional execution
<c:choose>, <c:when> and <c:otherwise>
<c:choose>
<c:when test="${user.role == 'member'}">
<p>Welcome, member!</p>
</c:when>
<c:otherwise>
<p>Welcome, guest!</p>
</c:otherwise>
</c:choose>
10
forEach Tag
Provides flexible iteration through a set of items
Targets include:
Collections, Maps, Iterators, Enumerations
Arrays
Comma-separated values
SQL ResultSets
Example:
<table>
<c:forEach items="${customers}" var=“cust">
<tr>
<td>${cust.name}</td>
<td>${cust.addr}</td>
</tr>
</c:forEach>
</table>
11
Anatomy of a Tag
Element
Attribute (optional)
Start tag
Body
(optional)
End tag
<tl:asis tab="5">
Instructions for logging in to the system:
(1)Enter your Patron identifier in ID field
(2)Enter assigned password in PW field
(3)Click on LOGIN button
</tl:asis>
12
Tag Examples
Basic
<tl:fullText />
With attributes
<tl:code language="java“/>
With attributes and a body
<tl:iterator times=10>
<p>"Hello world."</p>
</tl:iterator>
Defining scripting variables
<tl:iterator name="list" id="customer”
type="domain.Customer">
<jsp:getProperty name="customer"
property="name" />
</tl:iterator>
13
Describing Tags to the JSP Container
Done with the taglib descriptor (TLD)
XML file
Describes the tag library
Files use the .tld extension
Defines the syntax of the tags (actions)
Defines the attributes (if any) for the tags
Specifies if the attribute is optional or required
Specifies the Java class that implements the tag
Specifies if the tag allows or uses a body
Used by the JSP container to validate the JSP at compile time
14
General Format of the TLD (1 of 2)
<?xml version="1.0" encoding="UTF-8"?>
Required
<taglib version="2.0"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/webjsptaglibrary_2_0.xsd">
<description>Tag Library from IBM Library System Info about TLD
</description>
<tlib-version>1.0</tlib-version>
<short-name>ilib</short-name>
<tag>
Tag
Info
Defines the date
tag
<name>date</name>
<tag-class>com.ibm.library.tag.FormattedDate</tag-class>
<body-content>empty</body-content>
<description>Display current date</description>
</tag>
15
General Format of the TLD (2 of 2)
<tag>
<name>date2</name>
Action
name
Tag handler class
implementation
<tag-class>com.ibm.library.tag.FormatDate2</tag-class>
<body-content>JSP</body-content>
How to process the body
<attribute>
Attribute name
(multiple
allowed)
<name>format</name>
<required>true</required>
</attribute>
</tag>
</taglib>
Optional (false) or
mandatory (true)
16
Location of TLD File
Resides in the META-INF directory or subdirectory when
deployed inside a JAR file
Resides in the WEB-INF directory or some subdirectory when
deployed directly into a Web application
XML Schema is located at URL:
http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd
17
JSP Taglib Directive
Taglib directive tells your JSP the prefix to be used for a
specific JSP tag library
Taglib
directive
Location of
TLD
<!DOCTYPE … >
<HTML>
<HEAD>
<%@ taglib uri="/WEB-INF/tld/taglib.tld" prefix="tl" %>
…
<TITLE>date test</TITLE>
</HEAD>
Prefix for this JSP
<BODY>
…
<tl:date format="full"/>
…
</BODY>
</HTML>
Taglib usage
18
Tag Handler Base Classes
Tag handlers must implement specific
interfaces or extend specific classes, and
must override key methods
These classes all reside in
javax.servlet.jsp.tagext
JSP 2.0 introduced
SimpleTag
19
“classic”
tags
Example Tag
The <transform> tag allows page developers to transform the
contained text in two ways:
Convert it to upper case
Hide it
The tag has a required attribute mode with the following
values:
upper
hide
The value of the attribute can be taken from a runtime
expression
<m:transform mode="upper">
<P>This is text to be transformed.</P>
</m:transform>
20
Processing Tags with Attributes: How It Works
1) Initialize and set
attributes (setMode())
2) Call doTag() method
<m:transform mode="upper">
<P>This is text to be
transformed.</P>
</m:transform>
21
What Needs to Be Done?
Create the TransformTag class
Update the TLD for the new date tag
Use the new <transform> tag in your JSPs
JSP
Page
TLD
22
handler
class
The TransformTag Class
package com.ibm.library.tag;
import
import
import
import
import
import
java.io.IOException;
java.io.StringWriter;
javax.servlet.jsp.JspException;
javax.servlet.jsp.JspWriter;
javax.servlet.jsp.tagext.JspFragment;
javax.servlet.jsp.tagext.SimpleTagSupport;
public class TransformTag extends SimpleTagSupport {
String mode = "";
public void setMode(String mode) {
this.mode = mode.toUpperCase();
}
// class continues on next page
23
The doTag() Method
public void doTag() throws JspException, IOException {
JspFragment body = getJspBody();
StringWriter oldbody = new StringWriter();
String newbody = null;
body.invoke(oldbody);
if (mode.equals("UPPER")) {
newbody = oldbody.toString().toUpperCase();
} else if (mode.equals("HIDE")) {
newbody = "";
} else {
newbody = oldbody.toString();
}
JspWriter out = getJspContext().getOut();
out.write(newbody);
}
24
The Taglib Descriptor
<?xml version="1.0" encoding="UTF-8"?>
<taglib version="2.0"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd ">
<description>Tag Library for Library System</description>
<tlib-version>1.0</tlib-version>
<short-name>ilib</short-name>
<tag>
<name>transform</name>
<tag-class>com.ibm.library.tag.TransformTag</tag-class>
<body-content>scriptless</body-content>
<attribute>
<name>mode</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
</taglib>
25
Using the <transform> Tag
<!DOCTYPE HTML PUBLIC
"-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib uri="WEB-INF/tld/mytags.tld" prefix="m" %>
<TITLE>transformDemo.jsp</TITLE>
</HEAD>
<BODY>
<H1>Demonstrate <transform> tag</H1>
<m:transform mode="UPPER">
<P>This is text to be
transformed</P>
</m:transform>
<P>This text is not
to be transformed</P>
</BODY>
</HTML>
26
Packaging
To facilitate reuse, the tag handler classes can be packaged
together
Place the class files in a JAR
Import the TLD into /WEB-INF/tld
Import the JAR into /WEB-INF/lib
An additional option is to
package the TLD with the
class files JAR
Application Developer provides
support for JSP tag library
resource references
Web Deployment Descriptor editor
Variables tab
Allows URI to be specified to reference the TLD
27
Checkpoint
1. What are some of the advantages of JSP custom tags?
2. What are the major steps that must be performed during JSP
custom tag development?
3. How are attributes’ values processed in a tag handler class?
4. What method of the SimpleTag interface does the main work
of processing a tag?
5. What is the purpose of the JSP taglib directive?
28
Checkpoint solutions
1. Advantages of custom tags include:
2. Make JSPs easier to develop, test, and maintain
3. Web developer can focus on presentation (role-based
developmental
4. Presentation logic is reusable
5. The major steps in JSP custom tag development are:
6. Design tags and attributes
7. Write tag handler class
8. Construct or modify TLD
9. Test in a JSP
10. Attribute values are processed in a tag handler class
through JavaBean-like setter methods.
11. doTag()
12. The taglib directive describes the location of the TLD and
designates the tag prefix.
29
Unit summary
Having completed this unit, you should be able to:
Describe the advantages of using JSP custom tags
List the major steps in developing and using JSP custom tags
Develop basic tag handler classes to implement JSP custom
tags
Create and modify taglib descriptor files
Package JSP taglib implementation classes and taglib
descriptor files
Understand the uses of the JSTL
Name some of the tags included in the JSTL and their
purposes
30
