Post on 12-Jan-2016
®
IBM Software Group
© 2007 IBM Corporation
JSP Custom Tags
4.1.0.3
2
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
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
Unit objectives
3
JSP Custom Tags Overview Nine standard actions must be provided by any compliant JSP
implementation:useBean, setProperty, getPropertyinclude, forwardplug-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” />
4
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 toolsHave different skills
Best PracticeMVC design is well establishedUse the right tools for the right jobs
5
Steps to Create and Use a Custom Tag Library To develop a tag, you need to:
Design your tags and attributesDeclare the tag in a tag library descriptor (TLD)Develop a tag handler classDevelop helper classes for the tag (if needed)
To use a custom tag, the JSP needs to:Include the tag library using the taglib directiveCode the custom tag with any needed attributesTest your tags
class 1
class 2
helperclass
TLDJSPPage
6
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>
7
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>
8
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
2
9
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 documentsInternationalization tagsSQL tags
J2EE 1.4 includes both JSP and JSTLJSTL taglibs included with Rational Application Developer
10
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>
11
forEach Tag Provides flexible iteration through a set of items Targets include:
Collections, Maps, Iterators, EnumerationsArraysComma-separated valuesSQL ResultSets
Example:<table> <c:forEach items="${customers}" var=“cust"> <tr> <td>${cust.name}</td> <td>${cust.addr}</td> </tr> </c:forEach></table>
12
Anatomy of a 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>
Start tag
Body(optional)
End tag
Attribute (optional)Element
13
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>
14
Describing Tags to the JSP Container Done with the taglib descriptor (TLD)
XML fileDescribes the tag libraryFiles 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
15
General Format of the TLD (1 of 2)
Defines the date tag
<?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">
<tag> <name>date</name> <tag-class>com.ibm.library.tag.FormattedDate</tag-class> <body-content>empty</body-content> <description>Display current date</description> </tag>
<description>Tag Library from IBM Library System </description> <tlib-version>1.0</tlib-version> <short-name>ilib</short-name>
Required
Info about TLD
Tag Info
16
General Format of the TLD (2 of 2)
<tag> <name>date2</name>
<tag-class>com.ibm.library.tag.FormatDate2</tag-class>
<body-content>JSP</body-content>
</tag></taglib>
<attribute>
<name>format</name> <required>true</required>
</attribute>
Action name
Tag handler class implementation
How to process the body
Attribute name (multiple allowed)
Optional (false) or mandatory (true)
17
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
18
JSP Taglib Directive Taglib directive tells your JSP the prefix to be used for a
specific JSP tag library
<!DOCTYPE … ><HTML><HEAD><%@ taglib uri="/WEB-INF/tld/taglib.tld" prefix="tl" %>…<TITLE>date test</TITLE></HEAD><BODY>…<tl:date format="full"/>…</BODY></HTML>
Taglib directive
Taglib usage
Location of TLD
Prefix for this JSP
19
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 “classic
” tags
20
Example Tag The <transform> tag allows page developers to transform the
contained text in two ways:Convert it to upper caseHide it
The tag has a required attribute mode with the following values:upperhide
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>
21
Processing Tags with Attributes: How It Works
<m:transform mode="upper"><P>This is text to be
transformed.</P></m:transform>
1) Initialize and set attributes (setMode()) 2) Call doTag() method
22
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
handlerclass
TLDJSPPage
23
The TransformTag Class
package com.ibm.library.tag;
import java.io.IOException;import java.io.StringWriter;import javax.servlet.jsp.JspException;import javax.servlet.jsp.JspWriter;import javax.servlet.jsp.tagext.JspFragment;import 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
24
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);}
25
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>
26
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>
27
Packaging To facilitate reuse, the tag handler classes can be packaged
togetherPlace the class files in a JARImport the TLD into /WEB-INF/tldImport the JAR into /WEB-INF/lib
An additional option is to package the TLD with the class files JAR
Application Developer providessupport for JSP tag library resource referencesWeb Deployment Descriptor editor
Variables tab
Allows URI to be specified to reference the TLD
28
Checkpoint1. 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?
29
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.
30
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
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
Unit summary