® IBM Software Group © 2007 IBM Corporation JSP Tag Files

2 After completing this unit, you should be able to:  Describe the use of JSP tag files  Call a tag file from a JSP  Pass body content, parameters and fragments to a tag file  Create a tag file and use the tag file directives  Package a tag file After completing this unit, you should be able to:  Describe the use of JSP tag files  Call a tag file from a JSP  Pass body content, parameters and fragments to a tag file  Create a tag file and use the tag file directives  Package a tag file Unit objectives

3 Overview of Tag Files  Another way to build custom actions  Tag files are JSPs with.tag or.tagx extensions  Allows non-Java developers to create reusable custom actions  Are automatically interpreted by the JSP container when placed in the /WEB-INF/tags folder  Custom action name is the same as the tag file name  Can be further organized in sub-folders of /WEB-INF/tags  Tag files are separate files that are called from JSPs Caller JSP …body content… TagFile2.tag TagFile1.tag

4 Calling a Tag File from a JSP  Resembles the invocation of a custom action  Tag files are automatically compiled into SimpleTags  More powerful than a that can only accept string parameters in the request  The tag file has access to implicit objects  The tag file can be passed  Body content: content in between the begin and end tag  Parameters  Fragments: individually named body content  For example to call details.tag from a caller JSP

5 Body Content from Caller JSP  Body Content can be: scriptless, tagdependent or empty  Tag files can use to use the body content  Caller JSP Uppercase this text  toUpper.tag (Tag file) Body Content

6 Parameters from Caller JSP  Passed as attributes to the tag file  Matches an attribute, with the same name, in the tag file  Can be a dynamic list of attributes  Handled in the tag file by a Map, thus order is not guaranteed  Can be mixed with defined attributes <info:details dyna1="first" loanedCopy="${item}" dyna2="second"/> defined parameter mixed in with 2 dynamic parameters parameter

7 Fragments from Caller JSP  Enable the calling page to pass in named fragments of body content  is used to define the main body content Welcome to the IBM Library System System has ${library.size} books ${item.title} ${item.author}

8 Tag Directive in Tag File  Attribute list for the directive  display-name  body-content: empty, scriptless or tagdependent  dynamic-attributes: name of the attribute map  small-icon  large-icon  description  example  language: scripting language  import: list of imports  pageEncoding  isELIgnored: true of false  For example

9 Attribute Directive in Tag File  Maps incoming parameters to variables  Attribute list for the directive  name  required: true or false  fragment: true or false  rtexprvalue: true or false  type: type of the attribute  description  For example attribute name="loanedCopy" required="true" type="com.ibm.library.model.LoanedCopy"%>  Dynamic attribute map, is defined in the tag directive ${element.key} : ${element.value}

10 Variable Directive in Tag File  Exposes variables to the calling page  A name can be given to the attribute or can be assigned from an attribute  if assigned from an attribute an alias needs to be defined to reference the attribute within the tag file  Attribute list for the directive  name-given or name-from attribute, with an alias  variable-class  scope: AT_BEGIN, AT_END or NESTED  description  For example 

11 Implicit Objects Available in a Tag File  Collection of objects available to the tag file  request: ServletRequest or HttpServletRequest  response: ServletResponse or HttpServletResponse  jspContext: JspContext for this tag file  session: HttpSession  application: ServletContext  out: JspWriter  config: ServletConfig

12 Example of Calling a Tag File  Tag invocation in ListItems.jsp (Caller JSP)  Tag definition in details.tag (Tag file) attribute name="loanedCopy" required="true" type="com.ibm.library.model.LoanedCopy"" %> Times Renewed = ${loanedCopy.timesRenewed}

13 Tag File with Body Content and a Fragment  Tag files can be passed fragments and evaluate the separately, using  Calling JSP Fragment 1 Body content  fragmentTest.tag

14 Tag File Packaging  A tag file is recognized by the container if placed in /WEB- INF/tags/ folder  Tag file does not need TLD  At tag file placed in the /META-INF/tags folder of a JAR file requires a TLD  The JAR file is placed in the /WEB-INF/lib folder  Tags can also be packaged as compiled Java classes

15 Checkpoint 1.Where can a tag file need to be placed to be automatically picked up by the JSP container? 2.Why use a tag file instead of writing a custom tag handler?

16 Checkpoint solutions 1./WEB-INF/tags 2.Allows non-Java developers to create reusable custom actions. Also externalizes any HTML and layout information that may creep into a tag handler class.

17 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  Create and call a tag file from a JSP 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  Create and call a tag file from a JSP Unit summary