Transcript
Page 1: Creating Custom JSP TagCreating Custom JSP Tag Libraries ... · Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6. Developed and

© 2010 Marty Hall

Creating Custom JSP TagCreating Custom JSP Tag Libraries: The Basics

Originals of Slides and Source Code for Examples:http://courses.coreservlets.com/Course-Materials/msajsp.html

Customized Java EE Training: http://courses.coreservlets.com/Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.

Developed and taught by well-known author and developer. At public venues or onsite at your location.2

© 2010 Marty Hall

For live Java EE training, please see training courses at http://courses.coreservlets.com/. at http://courses.coreservlets.com/.

Servlets, JSP, Struts, JSF 1.x, JSF 2.0, Ajax (with jQuery, Dojo, Prototype, Ext-JS, Google Closure, etc.), GWT 2.0 (with GXT),

Java 5, Java 6, SOAP-based and RESTful Web Services, Spring, gHibernate/JPA, and customized combinations of topics.

Taught by the author of Core Servlets and JSP, More Servlets and JSP and this tutorial Available at public

Customized Java EE Training: http://courses.coreservlets.com/Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.

Developed and taught by well-known author and developer. At public venues or onsite at your location.

Servlets and JSP, and this tutorial. Available at public venues, or customized versions can be held on-site at your

organization. Contact [email protected] for details.

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Agenda

• What are tags? Why use them?g y• Java-based tags

– Components of a tag library– Basic tags– Tags that use attributes

Tags that use body content– Tags that use body content– Tags that optionally use body content

• JSP-based tags (tag files)JSP based tags (tag files)– Components of a tag library– Basic tags– Tags that use attributes– Tags that use body content

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© 2010 Marty Hall

Intro

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Developed and taught by well-known author and developer. At public venues or onsite at your location.5

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Uses of JSP Constructs

• Scripting elements calling servletScripting elements calling servlet code directly

• Scripting elements calling servlet

SimpleApplication

g gcode indirectly (by means of utility classes)B• Beans

• Servlet/JSP combo (MVC)MVC ith JSP i l• MVC with JSP expression language

• Custom tagsMVC ith b t t d

ComplexApplication • MVC with beans, custom tags, and

a framework like JSF 2.06

Application

Tag Examples

Blah, blah, blah. <mytags:showDate/>Blah blah blah <mytags:showDate format "short"/>Blah, blah, blah. <mytags:showDate format="short"/>Blah, blah, blah.

<mytags:emphasize color="red" blink="true" size="100">This is a very important message

</mytags:emphasize>

Blah, blah, blah.

<mytags:translate language="spanish">Hello World

</mytags:translate></mytags:translate>

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© 2010 Marty Hall

Java-Based Tags

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Developed and taught by well-known author and developer. At public venues or onsite at your location.8

Components That Make Up a Tag LibraryTag Library

• The Tag Handler Class– Java code that says what to output– Must implement javax.servlet.jsp.tagext.SimpleTag

Usually extends SimpleTagSupport– Usually extends SimpleTagSupport– Goes in same directories as servlet class files and beans

• The Tag Library Descriptor FileThe Tag Library Descriptor File– XML file describing tag name, attributes, and

implementing tag handler class– Goes under WEB-INF

• The JSP FileI t t lib ( f i URL f d i t fil )– Imports a tag library (referencing URL of descriptor file)

– Defines tag prefix– Uses tags9

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Defining a Simple Tag Handler ClassClass

• Extend the SimpleTagSupport class• Import needed packages

– import javax.servlet.jsp.*;import javax servlet jsp tagext *;import javax.servlet.jsp.tagext.*;import java.io.*;

• Override doTagg– Obtain the JspWriter with getJspContext().getOut()– Use the JspWriter to generate output– Code gets called at request time

• Tag instances are not reused like servlet instances, so no worry about race conditions, even if you have instance y yvariables

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Defining a Simple Tag Handler Class: ExampleClass: Example

package coreservlets.tags;

import javax.servlet.jsp.*;import javax.servlet.jsp.tagext.*;import java.io.*;p jimport java.math.*;import coreservlets.Primes;

public class SimplePrimeTag extends SimpleTagSupport {protected int length = 50;

bli id d T () th J E ti IOE ti {public void doTag() throws JspException, IOException {JspWriter out = getJspContext().getOut();BigInteger prime = Primes nextPrime(Primes random(length));Primes.nextPrime(Primes.random(length));

out.print(prime);}

}11

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Defining a Simple Tag Library DescriptorDescriptor

• Start with XML header• Top-level element is taglib

– Just use tlib-version and short-name as in exampleE h t d fi d b l t ith• Each tag defined by tag element with:– description, which gives short info. Optional.

name which defines the base tag name– name, which defines the base tag name. – tag-class, which gives the fully qualified class name of

the tag handler. – body-content, which specifies if tag is standalone or

contains content between start and end tag. • You can have multiple tag entries in each TLD file• You can have multiple tag entries in each TLD file• Put TLD file somewhere under WEB-INF

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TLD File for SimplePrimeTag

<?xml version="1.0" encoding="UTF-8" ?><taglib 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/j2eehttp://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"version="2.0"><tlib ersion>1 0</tlib ersion><tlib-version>1.0</tlib-version><short-name>csajsp-taglib</short-name>

<tag><description>Outputs 50-digit primes</description><description>Outputs 50 digit primes</description><name>simplePrime</name><tag-class>coreservlets.tags.SimplePrimeTag</tag-class><body-content>empty</body-content>

</tag></tag>...

</taglib>

• Don’t memorize XML header and standard part; download and modify online versionpart; download and modify online version– The important thing is to know how to write tag entries– Place TLD file somewhere under WEB-INF13

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Accessing Custom Tags From JSP FilesJSP Files

• Import the tag library– Specify location of TLD file

<%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld"prefix="csajsp" %>prefix csajsp %

– Define a tag prefix (namespace)<%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld"

fi " j " %>prefix="csajsp" %>

• Use the tags<prefix:tagName />– <prefix:tagName />

• Tag name comes from TLD file• Prefix comes from taglib directive

j i l i /– E.g., <csajsp:simplePrime />

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Using simplePrime Tag

...<BODY><BODY><H1>Some 50-Digit Primes</H1>

<%@ taglib uri="/WEB-INF/tlds/csajsp-taglib tld"<%@ taglib uri= /WEB INF/tlds/csajsp taglib.tld prefix="csajsp" %>

<UL><LI><csajsp:simplePrime/>j p p /<LI><csajsp:simplePrime/><LI><csajsp:simplePrime/><LI><csajsp:simplePrime/>j p p

</UL>

</BODY></HTML>

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Using simplePrime Tag:ResultResult

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Assigning Attributes to Tags

• Allowing tags like– <prefix:name

attribute1="value1" attribute2="value2"attribute2 value2 ... attributeN="valueN"

/>/>

• Tags are still standalone– No body content between start and end tagsNo body content between start and end tags

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Attributes: The Tag Handler ClassThe Tag Handler Class

• Use of an attribute called attribute1i l l i ll h d ll dsimply results in a call to a method called setAttribute1

Attribute value is supplied to method as a String– Attribute value is supplied to method as a String

• Example– To supportTo support

<prefix:tagName attribute1="Test" />

add the following to tag handler class:

bli id ib ( i l ) {public void setAttribute1(String value1) {doSomethingWith(value1);

}18

Attributes: PrimeTag.java

package coreservlets.tags;

public class PrimeTag extends SimplePrimeTag {public void setLength(String length) {p g g gtry {

this.length = Integer.parseInt(length);} catch(NumberFormatException nfe) {} catch(NumberFormatException nfe) {

this.length = 50;}

}}

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Attributes: The Tag Library Descriptor FileThe Tag Library Descriptor File

• The tag element must contain a nested l tattribute element

• The attribute element has three further-nested elementsnested elements– name, a required element that defines the case-sensitive

attribute name. – required, a required element that stipulates whether the

attribute must always be supplied (true) or is optional (false)(false).

– rtexprvalue, an optional attribute that indicates whether the attribute value can be a JSP expression like p<%= expression %> (true) or whether it must be a fixed string (false). The default value is false.

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TLD File for PrimeTag

...<taglib ><taglib ...>

...<tag>

<description>Outputs an N-digit prime</description><description>Outputs an N digit prime</description><name>prime</name><tag-class>coreservlets.tags.PrimeTag</tag-class><body-content>empty</body-content><body content>empty</body content><attribute>

<name>length</name><required>false</required>equ ed a se / equ ed

</attribute></tag>...

</taglib>

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Using prime Tag

...<BODY><BODY><H1>Some N-Digit Primes</H1>

<%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld" g j p gprefix="csajsp" %>

<UL><LI>20-digit: <csajsp:prime length="20"/>

40 di i j i l h 40 /<LI>40-digit: <csajsp:prime length="40"/><LI>80-digit: <csajsp:prime length="80"/><LI>Default (50-digit): <csajsp:prime/>

</UL></UL>

</BODY></HTML></HTML>

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Using prime Tag: Result

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Including the Tag Body

• Simplest tags– <prefix:tagName/>

• Tags with attributesfi N 1 " l1" /– <prefix:tagName att1="val1" ... />

• Now<prefix:tagName>– <prefix:tagName>Scriptless JSP Content</prefix:tagName>

– <prefix:tagName att1="val1" ... >Scriptless JSP ContentScriptless JSP Content</prefix:tagName>

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Including Tag Body:The Tag Handler ClassThe Tag Handler Class

• Call getJspBody().invoke(null);g p y() ( )

public void doTag() throws ... {JspWriter out = getJspContext().getOut();out.print("...");getJspBody().invoke(null);out.print("...");p ( );

}

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Including Tag Body:HeadingTag javaHeadingTag.java

public class HeadingTag extends SimpleTagSupport {private String align;p g gprivate String bgColor;private String border;private String fgColor;private String font;private String font;private String size;

public void setAlign(String align) {this align = align;this.align = align;

}

public void setBgColor(String bgColor) {thi b C l b C lthis.bgColor = bgColor;

}

public void setBorder(String border) {this.border = border;

}…

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Including Tag Body:HeadingTag java (Continued)HeadingTag.java (Continued)

public void doTag() throws JspException, IOException {public void doTag() throws JspException, IOException {JspWriter out = getJspContext().getOut();out.print("<TABLE ALIGN=\"" + align + "\"\n" +

" BGCOLOR=\"" + bgColor + "\"\n" +" BORDER=" + border + "\">\n");

out.print("<TR><TH>");out.print("<SPAN STYLE=\"color: " + fgColor + ";\n" +

" font-family: " + font + ";\n" + font-family: + font + ;\n +" font-size: " + size + "px; " +"\">\n");

// Output content of the bodygetJspBody().invoke(null);out.println("</SPAN></TH></TR></TABLE>" +

"<BR CLEAR=\"ALL\"><BR>");}}

}

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Using Tag Body:The Tag Library Descriptor FileThe Tag Library Descriptor File

• Only difference is body-content elementSh ld b i tl i d f t– Should be scriptless instead of empty:<tag><name>…</name><tag-class> </tag-class><tag class>…</tag class><body-content>scriptless</body-content>

</tag>

• Legal values for body-content• Legal values for body-content– empty: no body content

• Body content is ignored even if supplied– scriptless: body content is included

• Can contain plain text, EL elements, other custom tags, and page directivesp g

• No explicit scripting allowed (<%= ... %>)– tagdependent: body content is processed by tag

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heading Tag: TLD File

<tag><description>Formats enclosed heading</description><description>Formats enclosed heading</description><name>heading</name><tag-class>coreservlets.tags.HeadingTag</tag-class><body-content>scriptless</body-content><body content>scriptless</body content><attribute>

<name>align</name><required>true</required><required>true</required>

</attribute><attribute>

<name>bgColor</name>a e bgCo o / a e<required>true</required>

</attribute> ...

</tag>

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Using heading Tag

…<BODY><%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld"

prefix="csajsp" %><csajsp:heading align="LEFT" bgColor="CYAN"

border="10" fgColor="BLACK"border="10" fgColor="BLACK" font="Arial Black" size="78">

First Heading</csajsp:heading><csajsp:heading align="RIGHT" bgColor="RED"

border="1" fgColor="YELLOW" font="Times New Roman" size="50">

Second HeadingSecond Heading</csajsp:heading><csajsp:heading align="CENTER" bgColor="#C0C0C0"

border="20" fgColor="BLUE" font="Arial Narrow" size="100">

Third Heading</csajsp:heading>

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Using heading Tag:ResultsResults

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Optional Tag Bodies

• First examples– No tag bodies

• body-content: empty• doTag does not call invoke(null)doTag does not call invoke(null)

• Most recent examples – Always included tag bodies

• body-content: scriptless• doTag calls invoke(null)

• Now:• Now: – Decide at request time whether or not to include tag body

• body-content: scriptless• doTag conditionally calls invoke(null)

– Depending on run-time information32

Optional Tag Bodies: DebugTag javaDebugTag.java

public class DebugTag extends SimpleTagSupport {p g g p g pp {public void doTag() throws JspException, IOException {PageContext context = (PageContext)getJspContext();HttpServletRequest request =(HttpServletRequest)context.getRequest();

// Output body of tag only if debug param is present.if (request.getParameter("debug") != null) {getJspBody().invoke(null);

}}

}

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TLD File for DebugTag

...<tag><tag>

<description>Conditionally outputs enclosed body

</description></description><name>debug</name><tag-class>coreservlets.tags.DebugTag</tag-class><b d t t> i tl </b d t t><body-content>scriptless</body-content>

</tag>...

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Using debug Tag

<%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld" prefix="csajsp" %>prefix= csajsp %>

Top of regular page. Blah, blah, blah. Yadda, yadda, yadda.<csajsp:debug><csajsp:debug><H2>Debug Info:</H2>********************<BR>R t H t ${ C t t t t H t}<BR>-Remote Host: ${pageContext.request.remoteHost}<BR>

-Session ID: ${pageContext.session.id}<BR>-The foo parameter: ${param.foo}<BR>********************<BR></csajsp:debug><P>Bottom of regular page. Blah, blah, blah. Yadda, yadda, yadda.

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Using debug Tag: Results

36

© 2010 Marty Hall

Using a Pseudo-URIUsing a Pseudo-URI Instead of TLD Location

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The <uri> Tag in TLD Files

• TLD files can define fake addresses? l i "1 0" di " 8" ?<?xml version="1.0" encoding="UTF-8" ?>

<taglib ...> ...<uri>http://anything/you/want</uri>

• JSP pages import TLD using fake address• JSP pages import TLD using fake address<%@ taglib uri="http://anything/you/want" ...%>

• Note: this address is totally made up: it just matches what is in the TLD file. JSP page does not connect to the Web to look for this address.

• Advantages– Can move/rename TLD file with no JSP code changes

• You can even bundle tag libraries in JAR files under WEB INF/lib and put• You can even bundle tag libraries in JAR files under WEB-INF/lib and put TLD files in META-INF in the JAR files

– If you write JSP pages using XML syntax, you can use an additional xmlnsentry to the root element and omit the @taglib declaration.

• Disadvantage– Confusing: JSP authors don’t know where TLD file is

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Example: The <uri> Tagp g

• TLD FileI WEB INF/ ld /fil ld

• JSP (Approach 1)<%@ t lib– In WEB-INF/tlds/file.tld

<?xml ... ?><taglib ...>

<%@ taglib uri="/WEB-INF/tlds/file.tld"prefix="myPrefix" %>

...<taglib ...><uri>

http://foo.com/bar</uri>

<myPrefix:myTag/>...

JSP (A h 2)<tag>

<name>myTag</name><tag-class>...</tag-class>

• JSP (Approach 2)<%@ taglib

uri="http://foo.com/bar"prefix="myPrefix" %>g g

<body-content>empty or scriptless

</body-content></tag>

prefix myPrefix %>...<myPrefix:myTag/>...

</tag></taglib>

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© 2010 Marty Hall

JSP-Based TagsJSP-Based Tags(Tag Files)( g )

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Tag Files: Custom Tags Using JSP SyntaxCustom Tags Using JSP Syntax

• Two Approaches– When there is lots of logic, use Java to create output

• Analagous to when you use servlets

– When there is lots of formatting use JSP to create output– When there is lots of formatting, use JSP to create output• Analagous to when you use JSP pages

• Pros– Very good for complex text formatting– Very concise

C• Cons– Not good for complicated logic

Runs only in JSP 2 0 and later– Runs only in JSP 2.0 and later• Java-based versions had “classic” syntax that worked in

older servers (e.g., BEA WebLogic 8.1, Oracle 9i AS)41

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Simple Standalone Tags

• Java-based approach requires three pieces– Java code that overrides doTag to generate output

• Strengths and weaknesses generally similar to those of servlets, but more cumbersome,

– Tag Library Descriptor (TLD) file that maps Java class name to tag nameJSP th t f t ifi l ti f TLD fil– JSP page that refers to specific location of TLD file

• JSP-based approach requires two piecesJSP code (tag file) that shows result– JSP code (tag file) that shows result

• /WEB-INF/tags/someName.tag

– No TLD file: tag name taken from tag-file name– JSP page that refers to directory containing tag file

• /WEB-INF/tags or a subdirectory thereof42

Tag Filesg

• Look just like regular JSP files, exceptM b l d i ( d ) WEB INF/– Must be located in (or under) WEB-INF/tags

– Must be named blah.tag, not blah.jsp– You use <%@ tag ... %> instead of <%@ page ... %>– You use predefined variable jspContext instead of pageContext

• But you can cast it to PageContext• Other variables (request, response, etc.) are the same

• Example

WEB-INF/tags/date.tag some-page.jsp

<%@ tag import="java.util.*" %>Date is <%= new Date() %>

<%@ taglib tagdir="/WEB-INF/tags"prefix="test" %>prefix= test %>

...<test:date/>

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Java-Based Tags: Code (Simple Standalone Tag)(Simple Standalone Tag)

package coreservlets.tags;

import javax.servlet.jsp.*;import javax.servlet.jsp.tagext.*;import java.io.*;p jimport java.math.*;import coreservlets.Primes;

public class SimplePrimeTag extends SimpleTagSupport {protected int length = 50;

bli id d T () th J E ti IOE ti {public void doTag() throws JspException, IOException {JspWriter out = getJspContext().getOut();BigInteger prime = Primes nextPrime(Primes random(length));Primes.nextPrime(Primes.random(length));

out.print(prime);}

}44

Java-Based Tags: TLD File(Simple Standalone Tag)(Simple Standalone Tag)

<?xml version="1.0" encoding="UTF-8" ?><taglib xmlns="http://java.sun.com/xml/ns/j2ee"<taglib xmlns http://java.sun.com/xml/ns/j2eexmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/j2eehttp://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"version="2.0"><tlib-version>1.0</tlib-version><short-name>csajsp-taglib</short-name>

<tag><description>Outputs 50-digit primes</description><name>simplePrime</name><tag-class>coreservlets.tags.SimplePrimeTag</tag-class><body-content>empty</body-content>

</tag>...

</taglib>

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Java-Based Tags: Usage in JSP(Simple Standalone Tag)(Simple Standalone Tag)...<BODY><BODY><H1>Some 50-Digit Primes</H1><%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld"

prefix="csajsp" %><UL><LI><csajsp:simplePrime/><LI><csajsp:simplePrime/><LI><csajsp:simplePrime/><LI><csajsp:simplePrime/><LI>< j i l P i /><LI><csajsp:simplePrime/>

</UL></BODY></HTML>

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Java-Based Tags: Result(Simple Standalone Tag)(Simple Standalone Tag)

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Tag Files: Tag Code(Simple Standalone Tag)(Simple Standalone Tag)

• WEB-INF/tags/simplePrime2.tag– Directory name is not arbitrary; must be in

/WEB-INF/tags or a subdirectory thereof

<%= coreservlets.Primes.nextPrime(coreservlets.Primes.random(50)) %>

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Tag Files: Usage in JSP(Simple Standalone Tag)(Simple Standalone Tag)...<BODY><BODY><H1>Some 50-Digit Primes</H1>

<%@ taglib tagdir="/WEB-INF/tags"<%@ taglib tagdir /WEB INF/tagsprefix="csajsp" %>

<UL><LI><csajsp:simplePrime2/>j p p /<LI><csajsp:simplePrime2/><LI><csajsp:simplePrime2/><LI><csajsp:simplePrime2/>j p p

</UL></BODY></HTML>

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Tag Files: Result(Simple Standalone Tag)(Simple Standalone Tag)

50

Tags with Attributes

• Java-based tags– For each attribute, add setAttributeName method to the

Java class– Attribute value usually explicitly stored in instance– Attribute value usually explicitly stored in instance

variable (field) of Java class– List each attribute explicitly in TLD file

• JSP-based tags (tag files)– Each attribute listed in tag file with @attribute

C l li t i d d t l (d f lt f l )• Can also list required and rtexprvalue (default false)

– Attribute value automatically stored in scoped variable (for access from expression language) and in local ( p g g )variable (for access from Java code)

– No TLD file51

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Java-Based Tags: Code(Tag with Attributes)(Tag with Attributes)package coreservlets.tags;

public class PrimeTag extends SimplePrimeTag {public void setLength(String length) {

try {try {this.length = Integer.parseInt(length);

} catch(NumberFormatException nfe) {thi l th 50this.length = 50;

}}

}

52

Java-Based Tags: TLD File(Tag with Attributes)(Tag with Attributes)

…<tag><tag>

<description>Outputs an N-digit prime</description><name>prime</name><tag-class>coreservlets tags PrimeTag</tag-class><tag class>coreservlets.tags.PrimeTag</tag class><body-content>empty</body-content><attribute>

<name>length</name><name>length</name><required>false</required>

</attribute></tag>/tag

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Java-Based Tags: Usage in JSP(Tag with Attributes)(Tag with Attributes)…<BODY><BODY><H1>Some N-Digit Primes</H1><%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld"

prefix="csajsp" %><UL>

<LI>20-digit: <csajsp:prime length="20" /><LI>40-digit: <csajsp:prime length="40" /><LI>80-digit: <csajsp:prime length="80" /><LI>Default (50-digit): <csajsp:prime />( g ) j p p /

</UL></BODY></HTML>

54

Java-Based Tags: Results(Tag with Attributes)(Tag with Attributes)

55

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Tag Files: Tag Code(Tag with Attributes)(Tag with Attributes)<%@ attribute name="length" required="false" %><%<% int len = 50;try {len = Integer.parseInt(length);

} catch(NumberFormatException nfe) {}%>%><%= coreservlets.Primes.nextPrime

(coreservlets.Primes.random(len)) %>

56

Tag Files: Usage in JSP(Tag with Attributes)(Tag with Attributes)…<BODY><BODY><H1>Some N-Digit Primes</H1><%@ taglib tagdir="/WEB-INF/tags"

prefix="csajsp" %><UL>

<LI>20-digit: <csajsp:prime2 length="20"/><LI>40-digit: <csajsp:prime2 length="40"/><LI>80-digit: <csajsp:prime2 length="80"/><LI>Default (50-digit): <csajsp:prime2/>( g ) j p p /

</UL></BODY></HTML>

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Tag Files: Results(Tag with Attributes)(Tag with Attributes)

58

Tags with Bodies

• Java-based tags– Change body-content from empty to scriptless (in TLD)– Call getJspBody().invoke(null)

Still need setter method and TLD entry for every attribute– Still need setter method and TLD entry for every attribute

• JSP-based tags (tag files)JSP based tags (tag files)– Use <jsp:doBody/> to output tag body– No major syntax changes– Access to attributes still much simpler

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Java-Based Tags: Code (Tag with Body)(Tag with Body)

public class HeadingTag extends SimpleTagSupport {private String align;p g gprivate String bgColor;private String border;private String fgColor;private String font;private String font;private String size;

public void setAlign(String align) {this align = align;this.align = align;

}

public void setBgColor(String bgColor) {thi b C l b C lthis.bgColor = bgColor;

}

public void setBorder(String border) {this.border = border;

}…

60

Java-Based Tags: Code (Tag with Body -- Continued)(Tag with Body -- Continued)

public void doTag() throws JspException, IOException {public void doTag() throws JspException, IOException {JspWriter out = getJspContext().getOut();out.print("<TABLE ALIGN=\"" + align + "\"\n" +

" BGCOLOR=\"" + bgColor + "\"\n" +" BORDER=" + border + "\">\n");

out.print("<TR><TH>");out.print("<SPAN STYLE=\"color: " + fgColor + ";\n" +

" font-family: " + font + ";\n" + font-family: + font + ;\n +" font-size: " + size + "px; " +"\">\n"); //

// Output content of the bodygetJspBody().invoke(null);out.println("</SPAN></TH></TR></TABLE>" +

"<BR CLEAR=\"ALL\"><BR>");}}

}

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Java-Based Tags: TLD File (Tag with Body)(Tag with Body)

...<tag>g

<description>Formats enclosed heading</description><name>heading</name><tag-class>coreservlets.tags.HeadingTag</tag-class><body content>scriptless</body content><body-content>scriptless</body-content><attribute>

<name>align</name><required>true</required>

</attribute><attribute>

<name>bgColor</name><required>true</required><required>true</required>

</attribute> ...

</tag>

62

Java-Based Tags: Usage in JSP (Tag with Body)(Tag with Body)

<BODY><%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld"g / / / j p g

prefix="csajsp" %><csajsp:heading align="LEFT" bgColor="CYAN"

border="10" fgColor="BLACK" font="Arial Black" size="78">font="Arial Black" size="78">

First Heading</csajsp:heading><csajsp:heading align="RIGHT" bgColor="RED"

border="1" fgColor="YELLOW" font="Times New Roman" size="50">

Second Heading</csajsp:heading></csajsp:heading><csajsp:heading align="CENTER" bgColor="#C0C0C0"

border="20" fgColor="BLUE" font="Arial Narrow" size="100">

Third Heading</csajsp:heading>

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Java-Based Tags: Results (Tag with Body)(Tag with Body)

64

Tag Files: Tag Code (Tag with Body)(Tag with Body)<%@ attribute name="align" required="true" %><%@ attribute name="bgColor" required="true" %><%@ attribute name= bgColor required= true %><%@ attribute name="border" required="true" %><%@ attribute name="fgColor" required="true" %><%@ attribute name="font" required="true" %><%@ attribute name="font" required="true" %><%@ attribute name="size" required="true" %><TABLE ALIGN="${align}"

BGCOLOR "${b C l }"BGCOLOR="${bgColor}"BORDER="${border}">

<TR><TH>$<SPAN STYLE="color: ${fgColor};

font-family: ${font};font-size: ${size}px;">

<jsp:doBody/></SPAN></TABLE><BR CLEAR="ALL"><BR>

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Tag Files: Usage in JSP (Tag with Body)(Tag with Body)

<BODY><%@ taglib tagdir="/WEB-INF/tags"g g / / g

prefix="csajsp" %><csajsp:heading2 align="LEFT" bgColor="CYAN"

border="10" fgColor="BLACK" font="Arial Black" size="78">font="Arial Black" size="78">

First Heading</csajsp:heading2><csajsp:heading2 align="RIGHT" bgColor="RED"

border="1" fgColor="YELLOW" font="Times New Roman" size="50">

Second Heading</csajsp:heading2></csajsp:heading2><csajsp:heading2 align="CENTER" bgColor="#C0C0C0"

border="20" fgColor="BLUE" font="Arial Narrow" size="100">

Third Heading</csajsp:heading2>

66

Tag Files: Results (Tag with Body)(Tag with Body)

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© 2010 Marty Hall

Wrap-Up

Customized Java EE Training: http://courses.coreservlets.com/Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.

Developed and taught by well-known author and developer. At public venues or onsite at your location.68

Open Source Tag Libraries

• JSP Standard Tag Library (JSTL)C d i l t l t– Covered in later lecture

• AjaxTags– Simple Ajax functionality without writing JavaScriptp j y g p

• http://ajaxtags.sourceforge.net/• DisplayTag

– Super-fancy table creatorSuper fancy table creator• http://displaytag.sourceforge.net/1.2/

• Listing of other open-source tag librarieshttp://ja a so rce net/open so rce/jsp tag libraries– http://java-source.net/open-source/jsp-tag-libraries

• Google queries and searching• Google maps wrappers• Menus• Menus• Paging of large data sets• Fancy UIs

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Summary: Java-Based Tags

• Tag handler classE t d Si l T S t– Extend SimpleTagSupport

– Override doTag– Get the JspWriter with getJspContext().getOut()

U h J W i– Use the JspWriter to generate output– Output tag body with getJspBody().invoke(null);– Define setBlah for each attribute named blah

• TLD File (/WEB-INF/.../somefile.tld)– <tag> ... </tag>

• Contains description (optional), name, tag-class, b d t t tt ib t ( f h tt ib t )body-content, attribute (one for each attribute)

– <uri>http://fake-address</uri> (optional)• JSP File

– <%@ taglib uri="/WEB-INF/.../somefile.tld" prefix="blah" %>• Or <%@ taglib uri="http://fake-address" prefix="blah" %>

– <blah:tagName/> or <blah:tagName>...</blah:tagName>70

Summary: Tag Files

• Tag File– /WEB-INF/tags/tagName.tag– Create chunk of JSP that generates the output

l ib i h %@ ib %– Declare attributes with <%@ attribute ...%>– Output attributes with ${attributeName}

Output the tag body with <jsp:doBody/>– Output the tag body with <jsp:doBody/>– Refactor Java code so methods take strings as args

• JSP FileJSP File– <%@ taglib tagdir="/WEB-INF/tags prefix="blah" %>– <blah:tagName/> or g

<blah:tagName>...</blah:tagName>

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© 2010 Marty Hall

Questions?Questions?

Customized Java EE Training: http://courses.coreservlets.com/Servlets, JSP, JSF 2.0, Struts, Ajax, GWT 2.0, Spring, Hibernate, SOAP & RESTful Web Services, Java 6.

Developed and taught by well-known author and developer. At public venues or onsite at your location.72


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