Using xsl:choose

The <xsl:choose> element is much like the Java switch statement, which lets you compare a test value against several possible matches. Suppose, for example, that we add COLOR attributes to each <PLANET> element in ch13_26.xml:

Listing ch13_26.xml

 <?xml version="1.0"?> <?xml-stylesheet type="text/xml" href="ch13_02.xsl"?> <PLANETS>  <PLANET COLOR="RED">  <NAME>Mercury</NAME>     <MASS UNITS="(Earth = 1)">.0553</MASS>     <DAY UNITS="days">58.65</DAY>     <RADIUS UNITS="miles">1516</RADIUS>     <DENSITY UNITS="(Earth = 1)">.983</DENSITY>     <DISTANCE UNITS="million miles">43.4</DISTANCE><!--At perihelion-->   </PLANET>  <PLANET COLOR="WHITE">  <NAME>Venus</NAME>     <MASS UNITS="(Earth = 1)">.815</MASS>     <DAY UNITS="days">116.75</DAY>     <RADIUS UNITS="miles">3716</RADIUS>     <DENSITY UNITS="(Earth = 1)">.943</DENSITY>     <DISTANCE UNITS="million miles">66.8</DISTANCE><!--At perihelion-->   </PLANET>  <PLANET COLOR="BLUE">  <NAME>Earth</NAME>     <MASS UNITS="(Earth = 1)">1</MASS>     <DAY UNITS="days">1</DAY>     <RADIUS UNITS="miles">2107</RADIUS>     <DENSITY UNITS="(Earth = 1)">1</DENSITY>     <DISTANCE UNITS="million miles">128.4</DISTANCE><!--At perihelion-->   </PLANET> </PLANETS>

Now say that we want to display the names of the various planets, formatted in different ways using HTML <B> , <I> , and <U> tags, depending on the value of the COLOR attribute. I can do this with an <xsl:choose> element. Each case in the <xsl:choose> element is specified with an <xsl:when> element, and you specify the actual test for the case with the test attribute. Here's what it looks like:

Listing ch13_27.xsl

 <?xml version="1.0"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="PLANETS">     <HTML>         <HEAD>             <TITLE>                 Planets             </TITLE>         </HEAD>         <BODY>             <xsl:apply-templates select="PLANET"/>         </BODY>     </HTML> </xsl:template> <xsl:template match="PLANET">     <xsl:choose>         <xsl:when test="@COLOR = 'RED'">             <B>                 <xsl:value-of select="NAME"/>             </B>         </xsl:when>         <xsl:when test="@COLOR = 'WHITE'">             <I>                 <xsl:value-of select="NAME"/>             </I>         </xsl:when>         <xsl:when test="@COLOR = 'BLUE'">             <U>                 <xsl:value-of select="NAME"/>             </U>         </xsl:when>         <xsl:otherwise>              <PRE>                  <xsl:value-of select="."/>              </PRE>         </xsl:otherwise>     </xsl:choose> </xsl:template> </xsl:stylesheet>

Note also the <xsl:otherwise> element in this example, which acts the same way as the default: case in a switch statement. That is, if no other case matches, the <xsl:otherwise> element is applied. Here is the result of this XSLT:

 <HTML>  <HEAD> <TITLE>                 Planets             </TITLE> </HEAD> <BODY> <B>Mercury</B> <I>Venus</I> <U>Earth</U> </BODY> </HTML>