5.2 Transforming Data: Using Apache Xalan to apply XSLT transformations

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5.2 Transforming DataUsing Apache Xalan to
apply XSLT transformations

• Marc Dumontier
• Blueprint Initiative
• Samuel Lunenfeld Research Institute
• Toronto, ON

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Outline

• Introduction to Apache Xalan.
• Use the Xalan interactive processor from the
  command line.
• Use the Xalan Java API to apply an XSLT
  transformation.
• Use the JSP Standard Tag Library to apply
  transformations

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Apache Xalan

• Fully compliant XSLT 1.0 processor
• Fully supports XPath 1.0
• Includes an Interpretive processor for debugging.
• Can be configured to work with any W3C compliant
  XML parser. Optimized for Xerces.
• Can process stream, SAX, or DOM input.
• Can output to a stream, SAX, or DOM

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Apache Xalan

• Transformations may be chained.
• Includes an applet wrapper.
• May be used in a servlet
• May be used from JavaServer Pages.
• Can be extended.

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Outline

• Introduction to Apache Xalan.
• Use the Xalan interactive processor from the
  command line.
• Use the Xalan Java API to apply an XSLT
  transformation.
• Use the JSP Standard Tag Library to apply
  transformations

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Applying transformation from the command line

• Use the interpretive processor for simple command
  line based transformations.
• Advantages
• Easier to debug by isolating transformation from
  a larger more complex system.
• Can see output of ltxslmessagegt to console.
  ltxslmessagegt is used for debugging. Similar to
  System.out.println().
• Quick to execute
• Simple to use

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Applying transformations from the command line
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Outline

• Introduction to Apache Xalan.
• Use the Xalan interactive processor from the
  command line.
• Use the Xalan Java API to apply an XSLT
  transformation.
• Use the JSP Standard Tag Library to apply
  transformations

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Using the Java API

• Prerequisites
• Must include necessary JAR files in your
  classpath such as xalan.jar, and an XML parser
  such as Apache Xerces.
• An XML document to transform, either from a file,
  W3C DOM structure, or string.
• A valid XSLT Stylesheet which describes the rules
  of transformation.

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Using the Java API - Example

• This program takes in an XML filename, and an
  XSLT filename, and writes the result of the
  transformation to standard output.
• The first step is to get the argument values and
  convert them to URIs (Uniform Resource
  Identifiers).
• The second step involves creating a
  TransformerFactory object. This object employs
  the factory pattern.
• The third step is to create a Transformer object
  for the XSLT stylesheet.
• The fourth step is to transform the XML document.

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Using the Java API - Example
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Using the Java API - Example
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Outline

• Introduction to Apache Xalan.
• Use the Xalan interactive processor from the
  command line.
• Use the Xalan Java API to apply an XSLT
  transformation.
• Use the JSP Standard Tag Library to apply
  transformations

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Using Xalan from JavaServer Pages

• The common pattern for doing XSLT transformation
  in Java Server Pages (JSP) is to use the JSP
  Standard Template Library.
• It is also possible to import the Xalan classes
  and embed Java code using the API.

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Introduction to JSTL

• JavaServer Pages Standard Tag Library (JSTL)
  encapsulates common JSP functionality into Tags.
• JSTL has support for common, structural tasks
  such as iteration and conditionals, tags for
  manipulating XML documents, internationalization
  tags, and tags for accessing databases using SQL.
  It also introduces the concept of an expression
  language to simplify page development.

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JSTL XML
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Core Tags

• Provides the basic functionality for accessing
  and parsing XML data.
• The parse tag parses an XML file and stores the
  result in a type of variable.
• The expr and set tags are for running XPath
  expressions. set can store the results into a
  scoped JSP attribute.

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Flow Control Tags

• Similar to XSLT.
• Allows for evaluating XPath expressions and
  creating control statements.
• for-each allows for iterating over a node-set.

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Transformation Tags

• Perform XSLT transformations!
• Optionally pass parameters to the stylesheet such
  as external information only known as runtime.

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Using Xalan from JavaServer Pages

• Theres some setup required!
• There are multiple ways of doing this, use what
  works. This technology is very new.
• You must import the tag library definitions.
• The files must then be mapped in web.xml
• The supporting JAR files must be in your web
  applications classpath (usually WEB-INF/lib).

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Using Xalan from JavaServer Pages
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Using Xalan from JavaServer Pages
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Parsing an XML document

• Must read in the XML as a string using the core
  tag import.
• Use the parse tag on this string variable to
  parse into a DOM structure.

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Parsing an XML document

• lt_at_ taglib uri"/tags/jstl-c" prefix"c" gt
• lt_at_ taglib uri"/tags/jstl-x" prefix"x" gt
• lthtmlgt
• ltheadgt
• lttitlegtParse XMLlt/titlegt
• lt/headgt
• ltbody bgcolor"FFFFFF"gt
• lth3gtParse XML demolt/h3gt
• lt!-- import and parse XML document --gt
• ltcimport varReader"xmlString"
  url"smallgame.xml"gt
• ltxparse var"document" xml"xmlString"/gt
• lt/cimportgt
• lt/bodygt
• lt/htmlgt

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Using XPath in JSTL

• lt_at_ taglib uri"/tags/jstl-c" prefix"c" gt
• lt_at_ taglib uri"/tags/jstl-x" prefix"x" gt
• lthtmlgt
• ltheadgt
• lttitlegtXPath Demolt/titlegt
• lt/headgt
• ltbody bgcolor"FFFFFF"gt
• lth3gtXPath demolt/h3gt
• lt!-- import and parse XML document --gt
• ltcimport varReader"xmlString"
  url"smallgame.xml"gt
• ltxparse var"document" xml"xmlString"/gt
• lt/cimportgt
• lt!-- execute XPath statement --gt
• ltxout select"document/game/seq/name"/gt

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Using XPath in JSTL
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Running a Transformation from JSTL

• Similar to the previous example, reading the XML
  file from disk is done with the import tag.
• The transform tag is used to transform the XML
  using the XSLT that must also be read in and
  parsed

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Running a Transformation from JSTL

• lt_at_ taglib uri"/tags/jstl-c" prefix"c" gt
• lt_at_ taglib uri"/tags/jstl-x" prefix"x" gt
• lt!-- import stylesheet --gt
• ltcimport var"stylesheet" url"xsl1.xsl"/gt
• lt!-- import and parse XML document --gt
• ltcimport varReader"xmlString"
  url"smallgame.xml"gt
• ltxparse var"document" xml"xmlString"/gt
• lt/cimportgt
• lt!-- transform XML document using stylesheet --gt
• ltxtransform xslt"stylesheet"
  xml"document" /gt

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Running a Transformation from JSTL
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Expression Language (EL)

• JSP 2.0 introduced Expression Language (EL).
• EL is used extensively in JSTL.
• EL expressions are found in the special holder
  .
• Attributes can be accessed through EL.
• Example pageContext.request.method could be
  equal to GET or POST

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LAB Section

• The purpose of this lab is to get a working
  knowledge of using xalan in the three methods
  described.
• Command Line
• Java API
• JSP/JSTL
• All Code and examples have been provided

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The Data

• The Data chosen for this lab is the XML output
  from apollo the sequence annotation tool.
• Apollo is a collaboration between the Drosophila
  Genome Project, the Sanger Institute and the EBI.
• GMOD has adopted Apollo for sequence annotation.
• The XML output generated is GameXML.

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Apollo
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The Source

• Use CVS to checkout the gamexml module. It
  includes the following
• A build.xml file for ant
• 2 GameXML files (game.xml, smallgame.xml)
• 2 XSLT stylesheets (game_transcript.xsl,
  game_sequence.xsl)
• game.dtd (no XML Schema available)
• MyTansformer

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Exercises

• Explore the project
• Run MyTransformer with an XML file and a XSLT
  Stylesheet.
• Install the Web Application into tomcat.
• Run all the JSPs and see how they work.
• Write your own JSP with JSTL tags for processing
  XML.