JSP 1.2

1
JSP 1.2 Custom Tags
2
Agenda

• What is and why custom tags?
• Components that make up custom tag architecture
• How to create custom tags?
• How does it work?
• JSTL

3
Evolution of Web tier technology
4
Web Application Designs
5
Standard Action Tags

• ltjspuseBeangt
• Instantiate Java Bean class without explicit Java
  programming language
• ltjspgetPropertygt
• Allow accessing bean properties
• ltjspsetPropertygt
• Allow setting bean properties

6
Standard Action Tags

• ltjspforwardgt
• Forwards request to HTML page, JSP, or servlet
• ltjspincludegt
• Includes data in a JSP page from another file
• ltjspplugingt
• Downloads Java plugin to browser to execute
  applet or bean

7
What is Custom Tag?
8
What is a Custom Tag?

• User defined JSP language elements
• Encapsulates recurring tasks
• Distributed in a custom made tag library

9
Custom Tag Features

• Be customized via attributes passed from the
  calling page
• Pass variables back to the calling page
• Access all the objects available to JSP pages
• Communicate with each other
• You can create and initialize a JavaBeans
  component, create a public EL variable that
  refers to that bean in one tag, and then use the
  bean in another tag

10
Custom Tag Examples

• Getting/setting Implicit objects
• Accessing database
• Flow control
• Iterations
• Many more

11
Ready-to-usable Custom Tag Library

• Java Standard Tag Library (JSTL)
• Tags for setting/getting attributes, iteration,
  etc
• Tags for database access
• Tags for internationalized formatting
• Tags for XML
• Jakarta-Taglibs

12
Why Custom Tags?
13
Why Custom Tags?

• Separate JSP page content from business (and
  other functionality) logic
• Encapsulate business logic
• Reusable Maintainable
• Easier to
• author manually and to be manipulated by tool
• Provide
• Portable semantics

14
Custom Tags vs. JavaBeans

• Custom tags can manipulate JSP contents while
  beans cannot
• Complex operations can be reduced to a
  significantly simpler form with custom tags than
  the beans
• Custom tags require quite a bit of more work to
  set up than do beans

15
Quick Introduction on Components that make up
Custom tag architecture
16
Three things make up custom tagarchitetecture

• Tag handler class
• Defines tag's behavior
• Tag library descriptor (TLD)
• Maps XML elements to tag handler class
• JSP file
• Uses tags

17
Steps for implementing custom tags

• Write tag handlers
• Write Tag library descriptor (TLD) file
• Write JSP pages that use tags

18
Tag handler class

• Implements
• javax.servlet.jsp.tagext.Tag or
• javax.servlet.jsp.tagext.Bodytag interface
• Usually extends
• javax.servlet.jsp.tagext.TagSupport or
• javax.servlet.jsp.tagext.BodyTagSupport class
• Located in the same directory as servlet class
  files
• /WEB-INF/classes/ltpackage-directory-structuregt

19
Example Tag Handler (page 1)ExampleTag.java

• package moreservlets.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• / Very simple JSP tag that just inserts a
  string
• ("Custom tag example...") into the output.
• The actual name of the tag is not defined
  here
• that is given by the Tag Library Descriptor
  (TLD)
• file that is referenced by the taglib
  directive
• in the JSP file.
• ltPgt
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.moreservlets.com/.
• copy 2002 Marty Hall may be freely used or
  adapted. /

20
Example Tag Handler (page 2)ExampleTag.java

• public class ExampleTag extends TagSupport
• public int doStartTag()
• try
• JspWriter out pageContext.getOut()
• out.print("Custom tag example "
• "(moreservlets.tags.ExampleTag)")
  
• catch(IOException ioe)
• System.out.println("Error in ExampleTag "
  ioe)
• return(SKIP_BODY)

21
Tag Library Descriptor (TLD)

• XML file that describes
• tag name
• bodycontent
• attributes
• tag handler class
• Container knows which tag is associated with
  which tag handler class via this file
• Located
• Usually under WEB-INF directory
• Location specified in JSP file
• Via uri attribute of taglib directive

22
Example TLD (page 1 ) msajsp-tags.tld

• 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
• lt!-- a tag library descriptor --gt
• lttaglibgt
• lttlibversiongt1.0lt/tlibversiongt
• ltjspversiongt1.1lt/jspversiongt
• ltshortnamegtmsajsp-tagslt/shortnamegt
• ltinfogt
• A tag library from More Servlets and
  JavaServer Pages,
• http//www.moreservlets.com/.
• lt/infogt

23
Example TLD (page 2) msajsp-tags.tld

• lttaggt
• ltnamegtexamplelt/namegt
• lttagclassgtmoreservlets.tags.ExampleTaglt/tagcla
  ssgt
• ltbodycontentgtemptylt/bodycontentgt
• ltinfogtSimplest example inserts one line of
  outputlt/infogt
• lt/taggt
• lttaggt
• ltnamegtsimplePrimelt/namegt
  lttagclassgtmoreservlets.tags.SimplePrimeTaglt/tagcla
  ssgt
• ltbodycontentgtemptylt/bodycontentgt
• ltinfogtOutputs a random 50-digit prime.lt/infogt
• lt/taggt
• ...
• lt/taglibgt

24
JSP page

• Declare the tag library via taglib directive
• Use tags using custom tag syntax

25
Declaring a tag library

• Include taglib directive before tags are used
• Syntax
• lt_at_ taglib prefix"myprefix" urimyuri gt
• prefix identifies the tag library
• uri uniquely identifies the tag library
  descriptor (TLD) directly or indirectly

26
Custom Tag Syntax in JSP page

• ltprefixtag attr1"value" ... attrN"value" /gt
• or
• ltprefixtag attr1"value" ... attrN"value" gt
• body
• lt/prefixtaggt
• prefix distinguishes tag library
• tag identifies a tag (within the tag library)
• attr1 ... attrN modify the behavior of the tag

27
Example JSP page SimpleExample.jsp

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• lt!--
• Illustration of very simple JSP custom tag.
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems Press,
• http//www.moreservlets.com/.
• (C) 2002 Marty Hall may be freely used or
  adapted.
• --gt
• ltHTMLgt
• ltHEADgt
• lt_at_ taglib uri"/WEB-INF/msajsp-taglib.tld"
  prefix"msajsp" gt
• ltTITLEgtltmsajspexample /gtlt/TITLEgt
• ltLINK RELSTYLESHEET
• HREF"JSP-Styles.css"
• TYPE"text/css"gt
• lt/HEADgt
• ltBODYgt
• ltH1gtltmsajspexample /gtlt/H1gt

28
Example Accessing SimpleExample.jsp
29
Sample codes we will use in this class
30
Usage Scenarios of Custom Tags
31
Usage Scenarios of Custom Tags(Common between
JSP 1.1 and 1.2)

• Defining a basic tag
• A tag without attributes or tag bodies
• Assigning attributes to tags
• Including tag body
• Optionally including tag body
• Manipulating tag body
• Including or manipulating tag body multiple times
• Using nested tags

32
Defining a basic tag
33
Defining a basic tag

• A tag without attributes or body
• Extend TagSupport class
• All you have to do is to override doStartTag()
  method
• doStartTag() method defines code that gets called
  at request time at the place where the element's
  start tag is found
• doStartTag() returns SKIP_BODY since the tag does
  not have a body
• It instructs the container to ignore any body
  content between start and end tags

34
Assigning attributes to tags
35
Why assigning attributes to tags?

• Provides a way to pass attribute/value pairs from
  JSP pages to custom tag handlers
• Custom tag handlers can use them in whatever
  business logic they have

36
Tag handler class

• Use of an attribute X in a JSP page results in a
  call to a method setX() in the tag handler class
• Tag handler must implement setX() method
• public void setX(String value1)
• doSomethingWith(value1)

37
Example Tag Handler (page 1) SimplePrimeTag.java

• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import java.math.
• import moreservlets.
• / Generates a prime of approximately 50 digits.
• (50 is actually the length of the random
  number
• generated -- the first prime above that
  number will
• be returned.)
• ltPgt
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.moreservlets.com/.
• copy 2002 Marty Hall may be freely used or
  adapted.
• /

38
Example Tag Handler (page 2) SimplePrimeTag.java

• 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)
• return(SKIP_BODY)

39
Example Tag Handler (page 3) PrimeTag.java

• package moreservlets.tags
• / Generates an N-digit random prime (default N
  50).
• Extends SimplePrimeTag, adding a length
  attribute
• to set the size of the prime. The doStartTag
• method of the parent class uses the len field
• to determine the length of the prime.
• ltPgt
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.moreservlets.com/.
• copy 2002 Marty Hall may be freely used or
  adapted.
• /

40
Example Tag Handler (page 4) PrimeTag.java

• public class PrimeTag extends SimplePrimeTag
• public void setLength(String length)
• try
• len Integer.parseInt(length)
• catch(NumberFormatException nfe)
• len 50
• / Servers are permitted to reuse tag
  instances
• once a request is finished. So, this resets
• the len field.
• /
• public void release()
• len 50

41
TLD

• Attributes must be declared inside tag element by
  means of attribute sub-elements
• Attribute element has 5 sub-elements of its own
• name (required)
• required (required)
• rtexprvalue (optional)
• type (optional)
• example (optional)

42
TLD Attribute's rtexprvalue/type subelements

• rtexprvalue (optional)
• true if attribute value can be lt expression gt
• attribute value can be determined at request time
• false if attribute value is a fixed string
  (default)
• type (optional)
• specifies the class to which the value of the
  rtexprvalue should be typecast
• only legal when rtexprvalue is set to true

43
Example TLD (page 1)

• 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
• lt!-- a tag library descriptor --gt
• lttaglibgt
• lttlibversiongt1.0lt/tlibversiongt
• ltjspversiongt1.1lt/jspversiongt
• ltshortnamegtmsajsp-tagslt/shortnamegt
• ltinfogt
• A tag library from More Servlets and
  JavaServer Pages,
• http//www.moreservlets.com/.
• lt/infogt

44
Example TLD (page 2)

• ...
• lttaggt
• ltnamegtprimelt/namegt
• lttagclassgtmoreservlets.tags.PrimeTaglt/tagclass
  gt
• ltbodycontentgtemptylt/bodycontentgt
• ltinfogtOutputs a random N-digit prime.lt/infogt
• ltattributegt
• ltnamegtlengthlt/namegt
• ltrequiredgtfalselt/requiredgt
• lt/attributegt
• lt/taggt
• ...
• lt/taglibgt

45
Example JSP Page (PrimeExample.jsp)

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• lt!-- Illustration of PrimeTag tag.
• Taken from More Servlets and JavaServer Pages
  from Prentice Hall and Sun Microsystems Press,
  http//www.moreservlets.com/.(C) 2002 Marty Hall
  may be freely used or adapted.
• --gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtSome N-Digit Primeslt/TITLEgt
• ltLINK RELSTYLESHEET
• HREF"JSP-Styles.css"
• TYPE"text/css"gt
• lt/HEADgt
• ltBODYgt
• ltH1gtSome N-Digit Primeslt/H1gt
• lt_at_ taglib uri"/WEB-INF/msajsp-taglib.tld"
  prefix"msajsp" gt
• ltULgt
• ltLIgt20-digit ltmsajspprime length"20" /gt
• ltLIgt40-digit ltmsajspprime length"40" /gt
• ltLIgt60-digit ltmsajspprime length"60" /gt

46
Example Accessing PrimeExample.jsp
47
Tag handler class

• doStartTag() method should return
  EVAL_BODY_INCLUDE
• doEndTag() gets called after body is evaluated
• return EVAL_PAGE for continued processing
• return SKIP_PAGE for aborting processing rest of
  the page

48
Example Tag Handler (page 1)HeadingTag.java

• package moreservlets.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• / Generates an HTML heading with the specified
  background
• color, foreground color, alignment, font, and
  font size.
• You can also turn on a border around it,
  which normally
• just barely encloses the heading, but which
  can also
• stretch wider. All attributes except the
  background
• color are optional.
• ltPgt
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.moreservlets.com/.
• copy 2002 Marty Hall may be freely used or
  adapted.
• /

49
Example Tag Handler (page 2)HeadingTag.java

• 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
• public void setColor(String color)
• this.color color
• ...

50
Example Tag Handler (page 3)HeadingTag.java

• 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)
• return(EVAL_BODY_INCLUDE) // Include tag
  body

51
Example Tag Handler (page 4)HeadingTag.java

• 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

52
TLD

• The bodycontent element should contain the value
  JSP
• ltbodycontentgtJSPlt/bodycontentgt

53
Example TLD

• lt?xml version"1.0" encoding"ISO-8859-1" ?gt
• lt!DOCTYPE ...gt
• lttaglibgt
• ...
• lttaggt
• ltnamegtheadinglt/namegt
• lttagclassgtmoreservlets.tags.HeadingTaglt/tagcla
  ssgt
• ltbodycontentgtJSPlt/bodycontentgt
• ltinfogtOutputs a 1-cell table used as a
  heading.lt/infogt
• ltattributegt
• ltnamegtbgColorlt/namegt
• ltrequiredgttruelt/requiredgt lt!-- bgColor is
  required --gt
• lt/attributegt
• ltattributegt
• ltnamegtcolorlt/namegt
• ltrequiredgtfalselt/requiredgt
• lt/attributegt ...

54
Example JSP Page (HeadingExample.jsp)

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• lt!--
• Illustration of HeadingTag tag.
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems Press,
• http//www.moreservlets.com/.
• (C) 2002 Marty Hall may be freely used or
  adapted.
• --gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtSome Tag-Generated Headingslt/TITLEgt
• lt/HEADgt
• ltBODYgt
• lt_at_ taglib uri"/WEB-INF/msajsp-taglib.tld"
  prefix"msajsp" gt
• ltmsajspheading bgColor"C0C0C0"gt
• Default Heading
• lt/msajspheadinggt
• ltPgt

55
Example JSP Page (HeadingExample.jsp)

• ltPgt
• ltmsajspheading bgColor"EF8429" fontSize"60"
  border"5"gt
• Large Bordered Heading
• lt/msajspheadinggt
• ltPgt
• ltmsajspheading bgColor"CYAN" width"100"gt
• Heading with Full-Width Background
• lt/msajspheadinggt
• ltPgt
• ltmsajspheading bgColor"CYAN" fontSize"60"
• fontList"Brush Script MT, Times,
  serif"gt
• Heading with Non-Standard Font
• lt/msajspheadinggt
• lt/BODYgt
• lt/HTMLgt

56
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57
Optionally Including Tag Body
58
Optionally Including Tag body

• Decision of usage of body content is decided at
  request time
• Body content is not modified

59
Tag handler class

• doStartTag() method returns either
  EVAL_BODY_INCLUDE or SKIP_BODY
• depending on the value of some request time
  expression, for example
• Call getRequest() from pageContext field of
  TagSupport
• Typecast the return of getRequest() to
  HttpServletRequest since getRequest() returns
  ServletRequest type

60
Example Tag Handler (page 1)DebugTag.java

• package moreservlets.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import javax.servlet.
• / A tag that includes the body content only if
• the "debug" request parameter is set.
• ltPgt
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.moreservlets.com/.
• copy 2002 Marty Hall may be freely used or
  adapted.
• /

61
Example Tag Handler (page 2)DebugTag.java

• 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)

62
Example TLD

• lt?xml version"1.0" encoding"ISO-8859-1" ?gt
• lt!DOCTYPE ...gt
• lttaglibgt
• ...
• lttaggt
• ltnamegtdebuglt/namegt
• lttagclassgtmoreservlets.tags.DebugTaglt/tagclass
  gt
• ltbodycontentgtJSPlt/bodycontentgt
• ltinfogtIncludes body only if debug param is
  set.lt/infogt
• lt/taggt
• ...

63
Example JSP Page (DebugExample.jsp)

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• lt!--
• Illustration of DebugTag tag.
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems Press,
• http//www.moreservlets.com/.
• (C) 2002 Marty Hall may be freely used or
  adapted.
• --gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtUsing the Debug Taglt/TITLEgt
• ltLINK RELSTYLESHEET
• HREF"JSP-Styles.css"
• TYPE"text/css"gt
• lt/HEADgt
• ltBODYgt
• ltH1gtUsing the Debug Taglt/H1gt
• lt_at_ taglib uri"/WEB-INF/msajsp-taglib.tld"
  prefix"msajsp" gt

64
Example JSP Page (DebugExample.jsp)

• ltmsajspdebuggt
• 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/msajspdebuggt
• ltPgt
• Bottom of regular page. Blah, blah, blah. Yadda,
  yadda, yadda.
• lt/BODYgt
• lt/HTMLgt

65
DebugTag without debug inputparameter
66
Accessing DebugExample.jsp with debugtrue
input param
67
Manipulating Tag Body
68
Tag handler class

• Tag handler class should extend BodyTagSupport
  class
• BodyTagSupport class has 2 convenience methods
• doAfterBody() override this method in order to
  manipulate the tag body
• return SKIP_BODY if no further body processing is
  needed
• return EVAL_BODY_TAG (JSP 1.1) or EVAL_BODY_AGAIN
  (JSP 1.2) if the body content needs to be
  evaluated and handled again
• getBodyContent() returns BodyContent object

69
BodyContent class

• An encapsulation of the evaluation of the body
• A subclass of JspWriter
• BodyContent class has 3 methods
• getEnclosingWriter() returns JspWriter
• getReader() returns a Reader that can read tag
  body
• getString() returns a String containing entire
  tag body

70
Example Tag Handler (page 1)FilterTag.java

• package moreservlets.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• import moreservlets.
• / A tag that replaces lt, gt, ", and with their
  HTML
• character entities (lt, gt, quot, and
  amp).
• After filtering, arbitrary strings can be
  placed
• in either the page body or in HTML
  attributes.
• ltPgt
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.moreservlets.com/.
• copy 2002 Marty Hall may be freely used or
  adapted.
• /

71
Example Tag Handler (page 2)FilterTag.java

• 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)
• // SKIP_BODY means we're done. If we wanted
  to evaluate
• // and handle the body again, we'd return
  EVAL_BODY_TAG
• // (JSP 1.1/1.2) or EVAL_BODY_AGAIN (JSP 1.2
  only)
• return(SKIP_BODY)

72
Example TLD

• lt?xml version"1.0" encoding"ISO-8859-1" ?gt
• lt!DOCTYPE ...gt
• lttaglibgt
• ...
• lttaggt
• ltnamegtfilterlt/namegt
• lttagclassgtmoreservlets.tags.FilterTaglt/tagclas
  sgt
• ltbodycontentgtJSPlt/bodycontentgt
• ltinfogtReplaces HTML-specific characters in
  body.lt/infogt
• lt/taggt
• ...

73
Example JSP Page (FilterExample.jsp)

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• lt!--
• Illustration of FilterTag tag.
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems Press,
• http//www.moreservlets.com/.
• (C) 2002 Marty Hall may be freely used or
  adapted.--gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtHTML Logical Character Styleslt/TITLEgt
• ltLINK RELSTYLESHEET
• HREF"JSP-Styles.css"
• TYPE"text/css"gt
• lt/HEADgt
• 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.

74
Example JSP Page (FilterExample.jsp)

• lt_at_ taglib uri"/WEB-INF/msajsp-taglib.tld"
  prefix"msajsp" gt
• ltTABLE BORDER1 ALIGN"CENTER"gt
• ltTR CLASS"COLORED"gtltTHgtExampleltTHgtResult
• ltTRgt
• ltTDgtltPREgtltmsajspfiltergt
• 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/msajspfiltergtlt/PREgt
• ltTDgt
• ltEMgtSome emphasized text.lt/EMgtltBRgt
• ltSTRONGgtSome strongly emphasized
  text.lt/STRONGgtltBRgt
• ltCODEgtSome code.lt/CODEgtltBRgt
• ltSAMPgtSome sample text.lt/SAMPgtltBRgt

75
To be added
76
Including or Manipulating Tag Body Multiple Times
77
Tag handler class

• Tag handler class should extend BodyTagSupport
  class
• doAfterBody() now returns EVAL_BODY_TAG
  (EVAL_BODY_AGAIN in JSP 1.2)

78
Example Tag Handler (page 1)RepeatTag.java

• package moreservlets.tags
• import javax.servlet.jsp.
• import javax.servlet.jsp.tagext.
• import java.io.
• / A tag that repeats the body the specified
• number of times.
• ltPgt
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems
  Press,
• http//www.moreservlets.com/.
• copy 2002 Marty Hall may be freely used or
  adapted.
• /

79
Example Tag Handler (page 2)RepeatTag.java
public class RepeatTag extends BodyTagSupport
private int reps public void setReps(String
repeats) try reps
Integer.parseInt(repeats)
catch(NumberFormatException nfe) reps
1
80
Example Tag Handler (page 3)RepeatTag.java
public int doAfterBody() if (reps-- gt 1)
BodyContent body getBodyContent()
try JspWriter out body.getEnclosingWr
iter() out.println(body.getString())
body.clearBody() // Clear for next
evaluation catch(IOException ioe)
System.out.println("Error in RepeatTag "
ioe) // Replace EVAL_BODY_TAG with
EVAL_BODY_AGAIN in JSP 1.2.
return(EVAL_BODY_TAG) else
return(SKIP_BODY)
81
Example TLD

• lt?xml version"1.0" encoding"ISO-8859-1" ?gt
• lt!DOCTYPE ...gt
• lttaglibgt ...
• lttaggt
• ltnamegtrepeatlt/namegt
• lttagclassgtmoreservlets.tags.RepeatTaglt/tagclas
  sgt
• ltbodycontentgtJSPlt/bodycontentgt
• ltinfogtRepeats body the specified number of
  times.lt/infogt
• ltattributegt
• ltnamegtrepslt/namegt
• ltrequiredgttruelt/requiredgt
• lt!-- rtexprvalue indicates whether
  attribute
• can be a JSP expression. --gt
• ltrtexprvaluegttruelt/rtexprvaluegt
• lt/attributegt
• lt/taggt
• ...

82
Example JSP Page (RepeatExample.jsp)

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• lt!--
• Illustration of RepeatTag tag.
• Taken from More Servlets and JavaServer Pages
• from Prentice Hall and Sun Microsystems Press,
• http//www.moreservlets.com/.
• (C) 2002 Marty Hall may be freely used or
  adapted.
• --gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtSome 40-Digit Primeslt/TITLEgt
• ltLINK RELSTYLESHEET
• HREF"JSP-Styles.css"
• TYPE"text/css"gt
• lt/HEADgt
• ltBODYgt
• ltH1gtSome 40-Digit Primeslt/H1gt
• Each entry in the following list is the first
  prime number

83
Example JSP Page (RepeatExample.jsp)

• lt_at_ taglib uri"/WEB-INF/msajsp-taglib.tld"
  prefix"msajsp" gt
• ltOLgt
• lt!-- Repeats N times. A null reps value means
  repeat once. --gt
• ltmsajsprepeat reps'lt request.getParameter("rep
  eats") gt'gt
• ltLIgtltmsajspprime length"40" /gt
• lt/msajsprepeatgt
• lt/OLgt
• lt/BODYgt
• lt/HTMLgt

84
To be added
85
More detailed information on How to declare
tag library using taglib directive
86
Declaring a tag library uri attribute(3
different ways - 2 on this slide)

• Direct reference to TLD file
• lt_at_ taglib prefix"tlt" uri"/WEB-INF/iterator.tld
  "gt
• Indirect reference to TLD file using a logical
  name
• lt_at_ taglib prefix"tlt" uri"/tlt"gt
• Mapping of the logical name to path to the TLD
  file has to be defined in web.xml
• ltjsp-configgt
• lttaglibgt
• lttaglib-urigt/tltlt/taglib-urigt
• lttaglib-locationgt/WEB-INF/iterator.tldlt/taglib
  -locationgt
• lt/taglibgt
• lt/jsp-configgt

87
Declaring a tag library uri attribute(3
different ways - 1 on this slide)

• Absolute URI - examples of JSTL tag libraries
• lt_at_ taglib prefix"core" uri"http//java.sun.com/
  jsp/jstl/core"gt
• lt_at_ taglib prefix"xml" uri"http//java.sun.com/j
  sp/jstl/xml"gt
• lt_at_ taglib prefix"fmt" uri"http//java.sun.com/j
  sp/jstl/fmt"gt
• lt_at_ taglib prefix"sql" uri"http//java.sun.com/j
  sp/jstl/sql"gt
• lt_at_ taglib prefix"fn" uri"http//java.sun.com/js
  p/jstl/functions"gt

88
More detailed information on How to Configure tag
library with Web application
89
Configuring tag library with individual Web app

• In unpacked form
• tag handler classes are packaged under the
  /WEB-INF/classes/ directory
• .tld file under the /WEB-INF/ directory
• In packaged form (.jar file)
• .jar file is in the /WEB-INF/lib/ directory

90
Configuring tag library globally(for all Web
apps on a server)

• For Tomcat of Java WSDP
• Cove .jar file (tag library) to
  ltJWSDP_HOMEgt/common/lib
• Any jar files under ltJWSDP_HOMEgt/common/lib will
  be available to all Web apps

91
How does it Work?
92
How does it work?

• JSP translator locates the TLD file via uri
  attribute of taglib directive
• The TLD file describes the binding between an
  action (tag handler) and a Tag
• Using a tag in a JSP page generates the
  appropriate servlet code
• The servlet code contains tag handler

93
Sequence of Calls from Container
94
TagSupport Implements Tag Interface
95
doStartTag() and doEndTag()

• doStartTag()
• Processes starting element (semantics)
• Returns EVAL_BODY_INCLUDE to process body
• Returns SKIP_BODY to skip body
• doEndTag()
• Completes element processing (flush)
• Returns EVAL_PAGE to continue processing
• Returns SKIP_PAGE to terminate processing
• Both can throw JspException

96
Calling Sequence from the Container
97
How Is a Tag Invoked?

• JSP technology creates (or reuses) a Tag class
  instance associated with the element in the page
  source
• Class is named in the TLD
• Container calls setPageContext() and setParent()
• parent (possibly null, unless nested)
• PageContext provides access to request,
  response, out, session, page and attributes
• Container calls setX() methods for attributes
  specified
• Container calls doStartTag() and doEndTag()
• Container invokes release() to free Tag instance
  for reuse

98
How Is a Tag Invoked?
setPageContext() setParent()
99
JSP Page Response Output

• The output of the page is written into a
  JSPWriter provided by the page implementation
• This is flushed to the output stream of the
  ServletResponse.

100
BodyTag, BodyTagSupport

• For manipulating or evaluating body multiple
  times, use BodyTagSupport which is BodyTag type
• Example of iteration
• such as order rows, search results and etc

101
How Does BodyTag Work?
102
BodyContent
103
Manipulating BodyContent (1)

• JSP technology creates a nested stream
  (BodyContent) to contain the body text
• The BodyContent is passed to the BodyTag via
  setBodyContent()
• doStartBody() is invoked
• doInitBody() is invoked
• The body text is evaluated into the BodyContent

104
Manipulating BodyContent (2)

• doAfterBody() is invoked
• It must process the content of the nested stream
  and write to nesting stream (out)
• It can cause the page to be re-evaluated (to
  support iterative tags) by returning
  EVAL_BODY_TAG
• Invoke doEndTag().

105
BodyTag Method Semantics

• doStartTag()
• Same as Tag semantic, except
• Returns EVAL_BODY_TAG to process body
• doBodyInit()
• Prepare to process body
• doAfterBody()
• Handle processed body in BodyContent
• Return EVAL_BODY_TAG to reprocess
• DoEndTag()
• Same as Tag Semantics

106
What is JSTL?

• Standard set of tag libraries
• Encapsulates core functionality common to many
  JSP applications
• iteration, conditionals, XML, database access,
  internationalized formatting

107
Why JSTL?

• You don't have to write them yourself
• You learn and use a single standard set of tag
  libraries that are already provided by compliant
  Java platforms
• Vendors are likely to provide more optimized
  implementation
• Portability of your applications are enabled

108
JSTL Tag Libraries

• Core (prefix c)
• Variable support, Flow control, URL management
• XML (prefix x)
• Core, Flow control, Transformation
• Internationalization (i18n) (prefix fmt)
• Locale, Message formatting, Number and date
  formatting
• Database (prefix sql)
• SQL query and update
• Functions (prefix fn)
• Collection length, String manipulation

109
Declaration of JSTL Tag Libraries

• Core
• lt_at_ taglib prefix"c" uri"http//java.sun.com/jsp
  /jstl/core" gt
• XML
• lt_at_ taglib prefix"x" uri"http//java.sun.com/jsp
  /jstl/xml" gt
• Internationalization (i18n)
• lt_at_ taglib prefix"fmt" uri"http//java.sun.com/j
  sp/jstl/fmt" gt
• Database (SQL)
• lt_at_ taglib prefix"sql" uri"http//java.sun.com/j
  sp/jstl/sql" gt
• Functions
• lt_at_ taglib prefix"fn" uri"http//java.sun.com/js
  p/jstl/functions" gt

110
JSTL Tag Library Jar Files

• Distributed as two jar files
• standard.jar
• jstl.jar
• Under JWSDP
• ltjwsdp-installgt/jstl/lib/standard.jar
• ltjwsdp-installgt/jstl/lib/jstl.jar
• How to configure them with your Web apps
• Load them automatically with every Web app
• copy them to ltjwsdp-installgt/common/lib
• Load them only with your app
• copy them to ltyour-app-rootgt/WEB-INF/lib

111
Core Tags Types (page 1)

• Variable support
• ltcsetgt
• ltcremovegt
• Conditional
• ltcifgt
• ltcchoosegt
• ltcwhengt
• ltcotherwisegt
• Iteration
• ltcforEachgt
• ltcforTokensgt

112
Core Tags Types (page 2)

• URL management
• ltcimportgt
• ltcparamgt
• ltcredirectgt
• ltcparamgt
• ltcurlgt
• ltcparamgt
• General purpose
• ltcoutgt
• ltccatchgt

113
Variable Support, ltcsetgt

• Sets the value of an EL variable or the property
  of an EL variable via var attribute in any of
  the JSP scopes via scope attribute
• page, request, session, application
• If the variable does not already exist, it gets
  created
• Variable can be set in 2 different ways
• ltcset var"foo" scope"session" value"..."/gt
• ltcset var"bookId" value"param.Remove"/gt
• ltcset var"foo"gtvalue to be setlt/csetgt

114
Example ltcsetgt definition

• ltcset var"customerTable" scope"application"gt
• lttable border"1"gt
• ltcforEach var"customer" items"customers"
  gt
• lttrgt
• lttdgtcustomer.lastNamelt/tdgt
• lttdgtltcout value"customer.address"
  default"no address specified"/gtlt/tdgt
• lttdgt
• ltcout value"customer.address"gt
• ltfont color"red"gtno address specifiedlt/fontgt
• lt/coutgt
• lt/tdgt
• lt/trgt
• lt/cforEachgt
• lt/tablegt
• lt/csetgt

115
Example ltcsetgt usage

• lth4gtUsing "customerTable" application scope
  attribute defined in Set.jsp a first timelt/h4gt
• ltcout value"customerTable"
  escapeXml"false"/gt
• lth4gtUsing "customerTable" application scope
  attribute defined in Set.jsp a second timelt/h4gt
• ltcout value"customerTable" escapeXml"false"
  /gt

116
Example ltcsetgt usage
117
Variable Support ltcremovegt

• Remove an EL variable
• ltcremove var"cart" scope"session"/gt

118
Conditional Tags

• Flow control tags eliminate the need for
  scriptlets
• Without conditional tags, a page author must
  generally resort to using scriptlets
• ltcif test..gt
• Conditional execution of its body according to
  value of a test attribute
• ltcchoosegt
• Performs conditional block execution by the
  embedded ltcwhengt and ltcotherwisegt sub tags
• if-then-else

119
Example ltcif test...gt

• ltcforEach var"customer" items"customers"gt
• ltcif test"customer.address.country
  'USA'"gt
• customerltbrgt
• lt/cifgt
• lt/cforEachgt

120
Example ltcchoosegt, ltcwhengt

• ltcforEach var"customer" items"customers"gt
• ltcchoosegt
• ltcwhen test"customer.address.country
  'USA'"gt
• ltfont color"blue"gt
• lt/cwhengt
• ltcwhen test"customer.address.country
  'Canada'"gt
• ltfont color"red"gt
• lt/cwhengt
• ltcotherwisegt
• ltfont color"green"gt
• lt/cotherwisegt
• lt/cchoosegt
• customerlt/fontgtltbrgt
• lt/cforEachgt

121
Iterator Tag ltcforEachgt

• Allows you to iterate over a collection of
  objects
• items represent the collection of objects
• var current item
• varStatus iteration status
• begin, end, step range and interval
• Collection types
• java.util.Collection
• java.util.Map
• value of var attribute should be of type
  java.util.Map.Entry

122
Example ltcforEachgt

• ltcforEach var"customer" items"customers"gt
• customerltbrgt
• lt/cforEachgt

123
Example ltcforEachgt, Range

• ltcforEach var"i" begin"1" end"10"gt
• i
• lt/cforEachgt

124
Example ltcforEachgt, Data types

• ltcforEach var"i" items"intArray"gt
• ltcout value"i"/gt
• lt/cforEachgt
• ltcforEach var"string" items"stringArray"gt
• ltcout value"string"/gtltbrgt
• lt/cforEachgt
• ltcforEach var"item" items"enumeration"
  begin"2" end"10" step"2"gt
• ltcout value"item"/gtltbrgt
• lt/cforEachgt
• ltcforEach var"prop" items"numberMap"
  begin"1" end"5"gt
• ltcout value"prop.key"/gt ltcout
  value"prop.value"/gtltbrgt
• lt/cforEachgt
• ltcforEach var"token" items"bleu,blanc,rouge"gt
• ltcout value"token"/gtltbrgtlt/cforEachgt

125
(No Transcript)
126
Example ltcforEachgt, Iteration status

• ltcforEach var"customer" items"customers"
  varStatus"status"gt
• lttrgt
• lttdgtltcout value"status.index"/gtlt/tdgt
• lttdgtltcout value"status.count"/gtlt/tdgt
• lttdgtltcout value"status.current.lastName
  "/gtlt/tdgt
• lttdgtltcout value"status.current.firstName
  "/gtlt/tdgt
• lttdgtltcout value"status.first"/gtlt/tdgt
• lttdgtltcout value"status.last"/gtlt/tdgt
• lt/trgt...
• lt/cforEachgt
• ltcforEach var"i" begin"100" end"200" step"5"
  varStatus"status"gt
• ltcif test"status.first"gt
• beginltcout value"status.begin"gtbeginlt/c
  outgt
• endltcout value"status.end"gtendlt/coutgt
  
• stepltcout value"status.step"gtsteplt/cou
  tgtltbrgt
• sequence
• lt/cifgt ...
• lt/cforEachgt

127
Example ltcforEachgt, Iteration status
128
Example ltcoutgt

• lttable border"1"gt
• ltcforEach var"customer" items"customers"gt
• lttrgt
• lttdgtltcout value"customer.lastName"/gtlt/t
  dgt
• lttdgtltcout value"customer.phoneHome"
  default"no home phone specified"/gtlt/tdgt
• lttdgt
• ltcout value"customer.phoneCell"
  escapeXml"false"gt
• ltfont color"red"gtno cell phone
  specifiedlt/fontgt
• lt/coutgt
• lt/tdgt
• lt/trgt
• lt/cforEachgt
• lt/tablegt

129
Example ltcoutgt
130
URL Import ltcimportgt

• More generic way to access URL-based resources
  (than ltjspincludegt)
• Absolute URL for accessing resources outside of
  Web application
• Relative URL for accessing resources inside of
  the same Web application
• More efficient (than ltjspincludegt)
• No buffering
• ltcparamgt tag can be used to specify parameters
  (like ltjspparamgt)

131
Example ltcimportgt Absolute URL

• ltblockquotegt
• ltexescapeHtmlgt
• ltcimport url"http//www.cnn.com/cnn.rss"/gt
• lt/exescapeHtmlgt
• lt/blockquotegt

132
Example ltcurlgt

• lttable border"1" bgcolor"dddddd"gt
• lttrgt
• lttdgt"base", paramABClt/tdgt
• lttdgt
• ltcurl value"base"gt
• ltcparam name"param" value"ABC"/gt
• lt/curlgt
• lt/tdgt
• lt/trgt
• lttrgt
• lttdgt"base", param123lt/tdgt
• lttdgt
• ltcurl value"base"gt
• ltcparam name"param" value"123"/gt
• lt/curlgt
• lt/tdgt
• lt/trgt
• lttrgt

133
ltcoutgt

• Evaluates an expression and outputs the result of
  the evaluation to the current JspWriter object
• Syntax
• ltcout value"value" escapeXml"truefalse"
  default"defaultValue" /gt
• If escapeXml is true, escape character conversion

134
Example ltcoutgt

• lttable border"1"gt
• ltcforEach var"customer" items"customers"gt
• lttrgt
• lttdgtltcout value"customer.lastName"/gtlt/t
  dgt
• lttdgtltcout value"customer.phoneHome"
  default"no home phone specified"/gtlt/tdgt
• lttdgt
• ltcout value"customer.phoneCell"
  escapeXml"false"gt
• ltfont color"red"gtno cell phone
  specifiedlt/fontgt
• lt/coutgt
• lt/tdgt
• lt/trgt
• lt/cforEachgt
• lt/tablegt

135
Database Tags

• All DB actions operate on a DataSource
• Access a DataSource
• Object provided by ltsqldataSourcegt action
• ltsqldataSource var"dataSource"
  driver"org.gjt.mm.mysql.Driver"
  url"jdbc..."/gtltsqlquery dataSource"dataSour
  ce" .../gt

136
Example ltsqlsetDataSourcegt

• ltsqlsetDataSource
• var"example"
• driver"com.pointbase.jdbc.jdbcUniversalDriver"
• url"jdbcpointbaseserver//localhost1092/jstl
  samplecreatetrue"
• /gt

137
Example ltsqltransactiongt ltsqlupdategt

• ltsqltransaction dataSource"example"gt
• ltsqlupdate var"newTable"gt
• create table mytable (
• nameid int primary key,
• name varchar(80)
• )
• lt/sqlupdategt
• ltsqlupdate var"updateCount"gt
• INSERT INTO mytable VALUES (1,'Paul
  Oakenfold')
• lt/sqlupdategt
• ltsqlupdate var"updateCount"gt
• INSERT INTO mytable VALUES (2,'Timo Maas')
• lt/sqlupdategt
• ...
• ltsqlquery var"deejays"gt
• SELECT FROM mytable

138
Function Tags

• ltfnlengthgt Length of collection of string
• ltfntoUpperCasegt, ltfntoLowerCasegt Change the
  capitalization of a string
• ltfnsubstringgt, ltfnsubstringBeforegt,
  ltfnsubstringAftergt Get a subset of a string
• ltfntrimgt Trim a string
• ltfnreplacegt Replace characters in a string
• ltfnindexOfgt, ltfnstartsWithgt, ltfnendsWith
  containsgt, ltfncontainsIgnoreCasegt Check if a
  string contains another string
• ltfnsplitgt, ltfnjoingt Split a string into an
  array,and join a collection into a string
• ltfnescapeXmlgt Escape XML characters in the
  string

139
Example

• lt-- truncate name to 30 chars and display it in
  uppercase --gt
• fntoUpperCase(fnsubstring(name, 0, 30))
• lt-- Display the text value prior to the first
  character --gt
• fnsubstringBefore(text, )
• lt-- Scoped variable "name" may contain
  whitespaces at the
• beginning or end. Trim it first, otherwise we end
  up with 's in the URL --gt
• ltcurl var"myUrl" value"base/cust/fntrim(n
  ame)"/gt
• lt-- Display the name if it contains the search
  string --gt
• ltcif test"fncontainsIgnoreCase(name,
  searchString)"gt
• Found name name
• lt/cifgt
• lt-- Display text value with bullets instead of
  - --gt
• fnreplace(text, -, 149)

140
I18N and Formatting Tags

• Setting locale
• ltfmtsetLocalegt Override client-specified locale
  for a page
• ltfmtrequestEncodinggt -Set the request's
  character encoding, in order to be able to
  correctly decode request parameter values whose
  encoding is different from ISO-8859-1

141
I18N and Formatting Tags

• MessagingTags
• ltfmtbundlegt-specify a resource bundle for a page
• ltfmtmessage keygt
• used to output localized strings
• ltfmtparamgt subtag provides a single argument
  (for parametric replacement) to the compound
  message or pattern in its parent message tag

142
I18N and Formatting Tags

• Number and Date formatting
• ltfmtformatNumbergt, ltfmtparseNumbergt
• ltfmtformatDategt, ltfmtparseDategt
• ltfmtsetTimeZonegt, ltfmttimeZone gt

143
Example

• ltfmtsetLocale value"de"/gt
• ltfmtbundle basename"org.apache.taglibs.standard.
  examples.i18n.Resources"gt
• ltfmtmessagegt
• greetingMorning
• lt/fmtmessagegt
• lt/fmtbundlegt

144
Example ltfmtsetLocalegt
145
Example

• ltjspuseBean id"now" class"java.util.Date" /gt
• ltfmtsetLocale value"en-US" /gt
• ltulgt
• ltligt Formatting current date as "GMT"ltbrgt
• ltfmttimeZone value"GMT"gt
• ltfmtformatDate value"now"
  dateStyle"full" timeStyle"full"/gt
• lt/fmttimeZonegt
• ltligt Formatting current date as "GMT100", and
  parsing
• its date and time componentsltbrgt
• ltfmttimeZone value"GMT100"gt
• ltfmtformatDate value"now" type"both"
  dateStyle"full"
• timeStyle"full"
  var"formatted"/gt
• ltfmtparseDate value"formatted"
  type"both" dateStyle"full"
• timeStyle"full" timeZone"PST"
  var"parsedDateTime"/gt
• Parsed date ltfmtformatDate
  value"parsedDateTime" type"date"
• 
  dateStyle"full"/gtltbrgt
• Parsed time ltfmtformatDate
  value"parsedDateTime" type"time"

146
Example using browser locale en-us