XSLT Programming Constructs

Transcription

1 XSLT Programming Constructs

2 Contents 1. Procedural programming in XSLT 2. Defining named template rules 3. Parameterizing XSLT style sheets 2

3 1. Procedural Programming in XSLT Declarative vs. procedural programming Support for variables in XSLT Declaring variables Using variables Making decisions Looping 3

4 Declarative vs Procedural Programming XSLT is a declarative language You declare template rules to define "how things should be done" You do not explicitly control the flow of control through the style sheet The XSLT processing engine (Xalan) controls the flow This is quite different from procedural languages In procedural languages, you define the flow of control As a gesture to procedural developers, the XSLT standard includes procedural language constructs Variables, decision-making constructs, and loops 4

5 Support for Variables in XSLT You can declare variables in a style sheet Use <xsl:variable> You can define variables at different scopes Global variables Local variables 5

6 Declaring Variables There are two ways to declare a variable To define a string, number, or boolean value <xsl:variable name="name-of-variable" select="value-of-variable"/> To define an XML-tree-fragment value <xsl:variable name="name-of-variable"> XML-tree-fragment </xsl:variable> Note: You cannot change the value of a variable after it has been assigned It's like a final variable in Java (or const in C/C++) 6

7 Example of Declaring Variables <?xml encoding="iso_8859-1"?> <xsl:stylesheet xmlns:xsl=" <xsl:variable name="currency-symbol" select="'s'" /> <xsl:variable name="table-header"> <thead style="background-color:darkblue; color:lightblue"> <td align="center" width="20%">emp number</td> <td align="left" width="50%">full name</td> <td align="right" width="30%">salary</td> </thead> </xsl:variable> <!-- Template rules --> </xsl:stylesheet> 7

8 Using Variables There are three ways to use variables To evaluate a text, numeric, or boolean variable within a template rule body: <xsl:value-of select="$name-of-variable" /> To copy an XML-tree-fragment variable into a template rule body: <xsl:copy-of select="$name-of-variable" /> To evaluate a text, numeric, or boolean variable in an attribute: <MyElement MyAttribute="{$name-of-variable}" /> 8

9 Using Variables: Example 1 <xsl:template match="/"> <table width="90%"> <xsl:copy-of select="$table-header"/> <tbody> <xsl:apply-templates select="company/employee"/> </tbody> </table> <xsl:template match="salary"> Salary <xsl:value-of select="$currency-symbol"/> <xsl:value-of select="."/> <xsl:template match="dailyrate"> Daily rate <xsl:value-of select="$currency-symbol"/> <xsl:value-of select="."/> UsingVariables1.xsl 9

10 Using Variables: Example 2 <xsl:variable name="align-number" select="'center'" /> <xsl:variable name="align-name" select="'left'" /> <xsl:variable name="align-salary" select="'right'" /> <xsl:variable name="table-header"> <thead style="background-color:darkblue; color:lightblue"> <td align="{$align-number}" width="20%">emp number</td> <td align="{$align-name}" width="50%">full name</td> <td align="{$align-salary}" width="30%">salary</td> </thead> </xsl:variable> <xsl:template match="employee"> <tr style="background-color:yellow"> <td align="{$align-number}"> </td> <td align="{$align-name}"> </td> <td align="{$align-salary}"> </td> </tr> UsingVariables2.xsl 10

11 Making Decisions You can make decisions in a template rule To make a one-way decision: <xsl:if test="test-expression"> template-body </xsl:if> To make a multi-way decision: <xsl:choose> <xsl:when test="test-expression"> template-body </xsl:when> <xsl:when test="test-expression"> template-body </xsl:when> <xsl:otherwise> template-body </xsl:otherwise> </xsl:choose> 11

12 Making Decisions: Example 1 <xsl:template match="name"> MakingDecisions1.xsl <xsl:value-of select="lastname"/>, <xsl:value-of select="firstname"/> <xsl:if test="../@jobtitle='director'"> [DIRECTOR] </xsl:if> <xsl:template match="salary"> Salary $ <xsl:value-of select="."/> <xsl:choose> <xsl:when test=". >= 70000"> [TAX BAND 1] </xsl:when> <xsl:when test=". >= 40000"> [TAX BAND 2] </xsl:when> <xsl:otherwise> </xsl:choose> [TAX BAND 3] </xsl:otherwise> 12

13 Making Decisions: Example 2 <xsl:template match="salary"> Salary $ <xsl:value-of select="."/> MakingDecisions2.xsl <xsl:choose> <xsl:when test=". >= 70000"> <b>[<i>tax BAND 1</i>]</b> </xsl:when> <xsl:when test=". >= 40000"> <b>[<i>tax BAND 2</i>]</b> </xsl:when> <xsl:otherwise> <b>[<i>tax BAND 3</i>]</b> </xsl:otherwise> </xsl:choose> 13

14 Making Decisions: Example 3 <xsl:template match="salary"> Salary $ <xsl:value-of select="."/> MakingDecisions3.xsl <xsl:variable name="tax-band"> <xsl:choose> <xsl:when test=". >= 70000">1</xsl:when> <xsl:when test=". >= 40000">2</xsl:when> <xsl:otherwise>3</xsl:otherwise> </xsl:choose> </xsl:variable> <b>[<i>tax BAND <xsl:value-of select="$tax-band"/> </i>]</b> 14

15 Making Decisions: Example 4 <xsl:template match="employee"> MakingDecisions4.xsl <xsl:variable name="row-col"> <xsl:choose> <xsl:when test="position() mod 2 = 0">pink</xsl:when> <xsl:otherwise>lightblue</xsl:otherwise> </xsl:choose> </xsl:variable> <tr style="background-color:{$row-col}"> <td align="center"> <xsl:value-of select="@empnum"/> </td> <td align="left"> <xsl:apply-templates select="name"/> </td> <td align="right"> <xsl:apply-templates select="salary DailyRate"/> </td> </tr> 15

16 Looping You can perform iterations in a template rule <xsl:for-each select="expression"> template-body </xsl:for-each> <xsl:for-each> vs. <xsl:apply-templates> <xsl:for-each> = "pull processing" Gathers matching nodes, and iterates through the nodes <xsl:apply-templates> = "push processing" Gathers matching nodes, and pushes the nodes out to the other template rules in the style sheet Note: you can define optional <xsl:sort> elements after the <xsl:for-each> start tag 16

17 Looping: Example <xsl:template match="/"> <table width="90%"> <thead > </thead> <tbody> <xsl:for-each select="company/employee"> <xsl:sort select="name/lastname"/> <tr style="background-color:yellow"> <td align="center"> <xsl:value-of </td> <td align="left"> <xsl:apply-templates select="name"/> </td> <td align="right"> Output all </td> employees </tr> </xsl:for-each> </tbody> </table> <xsl:apply-templates select="salary DailyRate"/> Looping.xsl 17

18 2. Defining Named Template Rules Recap of applied template rules What is a named template rule? Example of named template rules Support for parameters in XSLT Declaring local parameters Passing parameter values 18

19 Recap of Applied Template Rules All of the template rules we have seen so far have been "applied template rules" The template rule has a match attribute, to indicate which content is transformed by the template rule <xsl:template match="match-criterion"> To instantiate the template rule Use <xsl:apply-templates> to gather nodes to be transformed <xsl:apply-templates select="selection-criterion" /> The XSLT processing engine instantiates the appropriate template rule(s), to transform the nodes 19

20 What is a Named Template Rule? A "named template rule" has a name rather than a match criterion Similar to functions in a procedural language Useful for performing common processing Also useful for simplifying template rules that would otherwise be too complex <xsl:template name="name-of-template-rule"> To call the template rule Use <xsl:call-template> <xsl:call-template name="name-of-template-rule" /> 20

21 Example of Named Template Rules <xsl:template match="employee"> <tr style="background-color:yellow"> <xsl:call-template name="displayemployeecolumns"/> </tr> NamedTemplateRules.xsl <xsl:template name="displayemployeecolumns"> <td align="center"> <xsl:value-of </td> <td align="left"> <xsl:apply-templates select="name"/> </td> <td align="right"> <xsl:apply-templates select="salary DailyRate"/> </td> 21

22 Support for Parameters in XSLT You can declare parameters in a style sheet Use <xsl:param> You can define parameters at different scopes Global parameters Local parameters 22

23 Declaring Local Parameters Declare <xsl:param> at the beginning of the template rule You can supply a default value for the parameter, in case the caller doesn't supply a value There are two ways to declare a local parameter To declare a parameter that has a string, number, or boolean default value: <xsl:param name="name-of-parameter" select="default-value-of-parameter"/> To declare a parameter that has an XML-tree-fragment default value: <xsl:param name="name-of-parameter"> XML-tree-fragment-default-value </xsl:param> 23

24 Example of Declaring Parameters <xsl:template name="displaycontent"> <xsl:param name="headbgcol" select="'darkblue'" /> <xsl:param name="headfgcol" select="'lightblue'"/> <xsl:param name="banner"> <h1>employee details</h1> </xsl:param> <body style="font-family:comic Sans MS; font-size:14"> <xsl:copy-of select="$banner"/> <table width="90%"> <thead style="background-color:{$headbgcol}; color:{$headfgcol}"> <td align="center" width="20%">emp number</td> <td align="left" width="50%">full name</td> <td align="right" width="30%">salary</td> </thead> <tbody> <xsl:apply-templates select="company/employee"/> </tbody> </table> </body> LocalParameters.xsl 24

25 Passing Parameter Values To pass a parameter into a template rule, use <xsl:with-param> when you apply/call the template rule To pass a string, number, or boolean parameter value <xsl:with-param name="name-of-parameter" select="value-for-parameter"/> To pass an XML-tree-fragment parameter value <xsl:with-param name="name-of-parameter"> XML-tree-fragment-for-parameter </xsl:with-param> 25

26 Example of Passing Parameter Values <xsl:template match="/"> <html> <xsl:call-template name="displaycontent"> <xsl:with-param name="headbgcol" select="'darkgreen'"/> <xsl:with-param name="banner"> <hr/><h3>employee information</h3><hr/><br/> </xsl:with-param> </xsl:call-template> </html> LocalParameters.xsl 26

27 3. Parameterizing XSLT Style Sheets Why parameterize a style sheet? Declaring global parameters in a style sheet Passing values in XMLSpy 27

28 Why Parameterize a Style Sheet? Examples of usage: To pass filter values into the style sheet To pass aesthetic information into the style sheet To pass text strings into the style sheet To pass filenames into the style sheet To pass conditional logic flags into the style sheet See notes below for some examples 28

29 Declaring and Using Global Parameters To declare global parameters: Declare a top-level <xsl:param> for each parameter To use a parameter: Use the syntax $param-name within a template rule <xsl:stylesheet xmlns:xsl=" <xsl:param name="minsal" select="0"/> <xsl:param name="maxsal" select=" "/> <xsl:template match="/"> <xsl:apply-templates select="company/employee[salary >= $MinSal and Salary <= $MaxSal]" /> </xsl:stylesheet> ParameterizedCompanyToHTML.xsl 29

30 Passing Values in XMLSpy XMLSpy allows you to specify parameters for style sheets Menu command: XSL/XQuery XSL Parameters / XQuery Variables Specify parameter names and values as required Then execute the style sheet as normal 30

31 Any Questions? 31