Creating Custom JSP Tag Libraries

1
Creating Custom JSP Tag Libraries

• http//java.sun.com/products/jsp/taglibraries.html
  tutorials
• Taken from Core Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems Press,
• http//www.coreservlets.com/.
• copy 2000 Marty Hall
• may be freely used or adapted.

2
JSP Komponenten
Anwendungs Logik
Java Entwickler
Daten Präsentation
DB
Daten Zugriff
WEB Designer
3
Beans

• ltjspuseBean id"wobs" class"jspcr.beans.weather.
  Observation"gt
• ltjspsetProperty
• name"wobs"
• property"airportCode"
• value"lt airportCode gt"/gt
• lt/jspuseBeangt

4
Custom Tags
Aktion starten

• ltjaxexample /gt Simple Tag
• ltjaxdebuggt Body Tag
• .
• lt/jaxdebuggt
• Kompaktere Syntax
• Inhalte bearbeiten
• Arbeitsaufwendiger

Aktion starten
Inhalt bearbeiten
Aktion starten
5
Installieren und starten

• Customtags benötigen folgende Elemente
• csajsp-taglib.tld Taglib Definition
• SimpleExample.jsp JSP
• ExampleTag.java Java Klasse
• Pfad

6
Custom Tags

• Ein Tag ist eine Klasse, die
• javax.servlet.jsp.tagext.Tag Interface
  implementiert.

7
Hello World Kochrezept

• 1. File HelloWorldTag.java im ../tag Ordner
  erstellen
• 2. import Anweisungen
• package com.jax.tag
• import javax.servlet.jsp.import
  javax.servlet.jsp.tagext.
• 3. Implementierung javax.servlet.jsp.tagext.Tag
  Interface
• public class HelloWorldTag implements Tag
• 4. Container Variablen
• private PageContext pageContextprivate Tag
  parent
• 5. Constructor
• public HelloWorldTag()
• super()

8
Hello World Kochrezept

• 6. Diese Methode wird beim Start-Tag ausgeführt
• public int doStartTag() throws javax.servlet.jsp.J
  spTagException
• return SKIP_BODY
• 7. Diese Methode wird beim End-Tag ausgeführt
• public int doEndTag() throws javax.servlet.jsp.Jsp
  TagException
• try
• pageContext.getOut().write("Hello World!")
• catch(java.io.IOException e)
• throw new JspTagException("IO Error "
  e.getMessage())
• return EVAL_PAGE // Den Rest der Seite
  weiterverarbeiten.

9
Hello World Kochrezept

• 8. Es braucht noch weitere Methoden
• public void release()
• 9.
• public void setPageContext(final
  javax.servlet.jsp.PageContext pageContext)
  this.pageContextpageContext
• 10.
• public void setParent(final javax.servlet.jsp.tage
  xt.Tag parent) this.parentparent
• 11. Finally, this method has to be implemented
• public javax.servlet.jsp.tagext.Tag getParent()
  
• return parent

10
Einfacher (extend TagSupport)

• package customtag.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• public class ExampleTag extends TagSupport
• public int doStartTag()
• try
• JspWriter out pageContext.getOut()
• out.print("Hello World"
• "(Hello World)")
• catch(IOException ioe)
• System.out.println("Error in ExampleTag "
  ioe)
• return(SKIP_BODY)

11
pageContext Methoden

• getOut
• getRequest
• getResponse
• getServletContext
• getSession
• JspWriter out pageContext.getOut()

12
SimpleExample.jsp

• ltHTMLgtltHEADgt
• lt_at_ taglib uri"csajsp-taglib.tld" prefix"jax"
  gt
• ltTITLEgtltjaxexample /gtlt/TITLEgtlt/HEADgt
• ltBODYgt
• ltH1gtltjaxexample /gtlt/H1gt
• ltjaxexample /gt
• lt/BODYgt
• lt/HTMLgt

13
taglib.tld (ins gleiche Verzeichnis wie die JSPs)

• lt?xml version"1.0" encoding"ISO-8859-1" ?gt
• lt!DOCTYPE taglib
• PUBLIC "-//Sun Microsystems, Inc.//DTD
  JSP Tag Library 1.1//EN"
• "http//java.sun.com/j2ee/dtds/web-jsptaglibrary_
  1_1.dtd"gt
• lttaglibgt
• lttlibversiongt1.0lt/tlibversiongt
• ltjspversiongt1.1lt/jspversiongt
• ltshortnamegtcsajsplt/shortnamegt
• lturigtlt/urigt
• ltinfogt
• Beispiel Tags für die Vorlesung JAX,
• http//www.ifi.unibas.ch
• lt/infogt
• lttaggt
• ltnamegtexamplelt/namegt
• lttagclassgtcustomtag.tags.ExampleTaglt/tagclassgt
  
• ltinfogtSimplest example inserts one line of
  outputlt/infogt
• ltbodycontentgtemptylt/bodycontentgt // JSP
  Inhalt wird als JSP interpretiert

14
SimplePrimeTag.java

• package customtag.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import java.math.
• import customtag.Primes
• public class SimplePrimeTag extends TagSupport
• protected int len 50
• public int doStartTag()
• try
• JspWriter out pageContext.getOut()
• BigInteger prime Primes.nextPrime(Primes.r
  andom(len))
• out.print(prime)
• catch(IOException ioe)
• System.out.println("Error generating prime
  " ioe)

15
PrimeTag.java

• package customtag.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import java.math.
• import customtag.tags.
• public class PrimeTag extends SimplePrimeTag
• public void setLength(String length)
• try
• len Integer.parseInt(length)
• catch(NumberFormatException nfe)
• len 50

16
taglib

• lttaggt
• ltnamegtsimplePrimelt/namegt
• lttagclassgtcustomtag.tags.SimplePrimeTaglt/tagcl
  assgt
• ltinfogtOutputs a random 50-digit prime.lt/infogt
• ltbodycontentgtemptylt/bodycontentgt
• lt/taggt
• lttaggt
• ltnamegtprimelt/namegt
• lttagclassgtcustomtag.tags.PrimeTaglt/tagclassgt
• ltinfogtOutputs a random N-digit prime.lt/infogt
• ltbodycontentgtemptylt/bodycontentgt
• ltattributegt
• ltnamegtlengthlt/namegt
• ltrequiredgtfalselt/requiredgt
• lt/attributegt
• lt/taggt

17
HeadingTag.jsp I

• package customtag.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• public class HeadingTag extends TagSupport
• private String bgColor // The one required
  attribute
• private String color null
• private String align"CENTER"
• private String fontSize"36"
• private String fontList"Arial, Helvetica,
  sans-serif"
• private String border"0"
• private String widthnull
• public void setBgColor(String bgColor)
• this.bgColor bgColor

18
HeadingTag.jsp II

• public int doStartTag()
• try
• JspWriter out pageContext.getOut()
• out.print("ltTABLE BORDER" border
• " BGCOLOR\"" bgColor "\""
• " ALIGN\"" align "\"")
• if (width ! null)
• out.print(" WIDTH\"" width "\"")
• out.print("gtltTRgtltTHgt")
• out.print("ltSPAN STYLE\""
• "font-size " fontSize "px "
  
• "font-family " fontList "
  ")
• if (color ! null)
• out.println("color " color "")
• out.print("\"gt ") // End of ltSPAN ...gt
• catch(IOException ioe)
• System.out.println("Error in HeadingTag "
  ioe)

19
HeadingTag.jsp III

• public int doEndTag()
• try
• JspWriter out pageContext.getOut()
• out.print("lt/SPANgtlt/TABLEgt")
• catch(IOException ioe)
• System.out.println("Error in HeadingTag "
  ioe)
• return(EVAL_PAGE) // Continue with rest of
  JSP page

20
HeadingExample.jsp

• ltHTMLgtltHEADgtltTITLEgtSome Tag-Generated
  Headingslt/TITLEgtlt/HEADgt
• ltBODYgtlt_at_ taglib uri"csajsp-taglib.tld"
  prefix"jax" gt
• ltjaxheading bgColor"C0C0C0"gt
• Default Heading
• lt/jaxheadinggt
• ltPgt
• ltjaxheading bgColor"BLACK" color"WHITE"gt
• White on Black Heading
• lt/jaxheadinggt
• ltPgt
• ltjaxheading bgColor"EF8429" fontSize"60"
  border"5"gt
• Large Bordered Heading
• lt/jaxheadinggt
• ltPgt
• ltjaxheading bgColor"CYAN" width"100"gt
• Heading with Full-Width Background
• lt/jaxheadinggt
• ltPgt
• ltjaxheading bgColor"CYAN" fontSize"60"

21
Debug.jsp

• ltHTMLgtltHEADgtltTITLEgtUsing the Debug
  Taglt/TITLEgtlt/HEADgt
• ltBODYgt
• ltH1gtUsing the Debug Taglt/H1gt
• lt_at_ taglib uri"csajsp-taglib.tld" prefix"jax"
  gt
• Top of regular page. Blah, blah, blah. Yadda,
  yadda, yadda.
• ltPgt
• ltjaxdebuggt
• ltBgtDebuglt/Bgt
• ltULgt
• ltLIgtCurrent time lt new java.util.Date() gt
• ltLIgtRequesting hostname lt request.getRemoteHo
  st() gt
• ltLIgtSession ID lt session.getId() gt
• lt/ULgt
• lt/jaxdebuggt

22
DebugTag.java

• package customtag.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import javax.servlet.
• public class DebugTag extends TagSupport
• public int doStartTag()
• ServletRequest request pageContext.getReques
  t()
• String debugFlag request.getParameter("debug
  ")
• if ((debugFlag ! null)
• (!debugFlag.equalsIgnoreCase("false")))
• return(EVAL_BODY_INCLUDE)
• else
• return(SKIP_BODY)

23
FilterTag.java

• package customtag.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import customtag.
• public class FilterTag extends BodyTagSupport
• public int doAfterBody()
• BodyContent body getBodyContent()
• String filteredBody ServletUtilities.filter(
  body.getString())
• try
• JspWriter out body.getEnclosingWriter()
• out.print(filteredBody)
• catch(IOException ioe)
• System.out.println("Error in FilterTag "
  ioe)
• return(SKIP_BODY)

24
FilterExample.jsp

• ltHTMLgtltHEADgtltTITLEgtHTML Logical Character
  Styleslt/TITLEgt
• ltBODYgt
• ltH1gtHTML Logical Character Styleslt/H1gt
• Physical character styles (B, I, etc.) are
  rendered consistently
• in different browsers. Logical character styles,
  however,
• may be rendered differently by different
  browsers.
• Here's how your browser
• (lt request.getHeader("User-Agent") gt)
• renders the HTML 4.0 logical character styles
• ltPgt
• lt_at_ taglib uri"csajsp-taglib.tld" prefix"jax"
  gt
• ltTABLE BORDER1 ALIGN"CENTER"gt
• ltTR CLASS"COLORED"gtltTHgtExampleltTHgtResult
• ltTRgt

25
FilterExample.jsp

• ltTDgtltPREgtltjaxfiltergt
• ltEMgtSome emphasized text.lt/EMgtltBRgt
• ltSTRONGgtSome strongly emphasized
  text.lt/STRONGgtltBRgt
• ltCODEgtSome code.lt/CODEgtltBRgt
• ltSAMPgtSome sample text.lt/SAMPgtltBRgt
• ltKBDgtSome keyboard text.lt/KBDgtltBRgt
• ltDFNgtA term being defined.lt/DFNgtltBRgt
• ltVARgtA variable.lt/VARgtltBRgt
• ltCITEgtA citation or reference.lt/CITEgt
• lt/jaxfiltergtlt/PREgt
• ltTDgtltEMgtSome emphasized text.lt/EMgtltBRgt
• ltSTRONGgtSome strongly emphasized
  text.lt/STRONGgtltBRgt
• ltCODEgtSome code.lt/CODEgtltBRgt
• ltSAMPgtSome sample text.lt/SAMPgtltBRgt
• ltKBDgtSome keyboard text.lt/KBDgtltBRgt
• ltDFNgtA term being defined.lt/DFNgtltBRgt
• ltVARgtA variable.lt/VARgtltBRgt
• ltCITEgtA citation or reference.lt/CITEgt

26
Taglibs
27
Praktikum

• Frohe Festtage
• Bean Übung beenden
• Beispiele Customtags durchspielen
• 3. Eine Taglib von Apache austesten
• http//jakarta.apache.org/taglibs/index.html