XSL for Business-to-Business (B2B) Communication

XSL for Business-to-Business (B2B) Communication

The previous section leveraged XSLT for document publishing. However, XSLT can also be used in for B2B communication—the process of exchanging data between two different companies. Developers can leverage XML to describe the data in a vendor-indepen-dent fashion. In the ideal case, both companies will agree upon a standard vocabulary for describing the data using a DTD or schema. The vocabulary is composed of the XML element names used in the XML document. However, in certain cases one of the compa-nies might like to use a different vocabulary. This is where XSL enters the picture.

The example in this section describes a B2B scenario between a training company, Hot Shot Training, and a software development company, AcmeSoft. The computer training company maintains a database for the students that have attended its courses. The train-ing company has developed an XML application that produces the list of students for a given class.

The management team at AcmeSoft would like to retrieve this list from the training com-pany’s XML application. However, once the data is retrieved, AcmeSoft would like to store the data in a different XML format using its own XML element names. The appli-cation interaction is illustrated in Figure 9.13.

The XML application at the training company is accessible using the HTTP protocol. The first step is to request the XML document from the training company. In step 2, the XML document is retrieved. In step 3, the document is transformed using the supplied XSLT style sheet. Finally, the desired output document is produced in step 4.

A sample output of the XML document is shown here:

<?xml version=”1.0”?> <trainingclass>

<title>J2EE Essentials</title> <start_date>24 Sep 2001</start_date> <end_date>28 Sep 2001</end_date> <location>Philadelphia, PA</location>

<student> <first_name>Riley</first_name> <last_name>Scott</last_name> <email>riley@acmesoft.web</email>

</student>

<student> <first_name>Torrance</first_name> <last_name>Lee</last_name>

<email>torrance.lee@acmesoft.web</email>

</student>

</trainingclass>

The development team at AcmeSoft has a different collection of element names to describe a training class. The desired output of the converted XML document for AcmeSoft is shown here:

<?xml version=”1.0”?> <employeelist>

<course_title>J2EE Essentials</course_title> <course_date start=”24 Sep 2001” end=”28 Sep 2001” /> <location>Philadelphia, PA</location>

<employee>

<name>

<first>Riley</first>

<last>Scott</last>

</name>

<email>riley.scott@acmesoft.web</email>

</employee>

<employee>

<name>

<first>Torrance</first>

<last>Lee</last>

</name>

<email>torrance.lee@acmesoft.web</email>

</employee>

</employeelist>

Notice in both instances that the data is the same; it’s simply in a different format. The format is different because of the element names used by AcmeSoft. In the context of AcmeSoft, there are no students on the payroll; instead, AcmeSoft has employees. Also, the AcmeSoft team has a different approach for storing the class date. Finally, notice that AcmeSoft uses a different structure for the employee name.

Therefore, a mechanism is needed to convert an XML document to another XML format. XSLT offers a solution to this problem. An XSL style sheet can be developed to convert the <trainingclass> document to the <employeelist> document. This approach will not require any changes by the training company. The training company can continue to publish XML documents for its training classes. The development team at AcmeSoft can develop an XSL style sheet that contains the transformation rules. Once the style sheet is developed, the XML document and style sheet can be passed to the XSLT processor, which will generate the desired XML document for <employeelist>.

Creating the XSL Style Sheet

The XSL style sheet will contain the template for the <employeelist> document, and the XSL elements will be leveraged to retrieve the data from the <trainingclass> docu-ment. The transformation is fairly straightforward, except for one area. The training com-pany describes the date for the class using the elements <start_date> and <end_date>, as shown here:

<start_date>24 Sep 2001</start_date> <end_date>28 Sep 2001</end_date>

AcmeSoft stores the date as a single element with two attributes for the start and end:

<course_date  start=”24  Sep  2001”  end=”28  Sep  2001”  />

In this case, <xsl:attribute> can be used to create attributes for <course_date>:

<course_date>

<xsl:attribute name=”start”><xsl:value-of select=”start_date”/> ➥ </xsl:attribute>

<xsl:attribute name=”end”><xsl:value-of select=”end_date”/></xsl:attribute> </course_date>

The <xsl:attribute> element creates attributes for the parent element. In this example, the parent element is course_date. This transformation will result in the following code:

<course_date  start=”24  Sep  2001”  end=”28  Sep  2001”  />

The complete code for the style sheet is shown in Listing 9.13.

LISTING 9.13  <install_dir>\ch9_xsl\public_html\b2b\train2employee.xsl

<?xml  version=”1.0”?>

<xsl:stylesheet  xmlns:xsl=”http://www.w3.org/1999/XSL/Transform”  version=”1.0”>

<xsl:template match=”/trainingclass”> <employeelist>

<course_title><xsl:value-of  select=”title”  /></course_title>

<!-- create attributes for the start and end course dates --> <course_date>

<xsl:attribute  name=”start”>

<xsl:value-of select=”start_date”/> </xsl:attribute>

<xsl:attribute  name=”end”>

<xsl:value-of select=”end_date”/> </xsl:attribute>

</course_date>

<location><xsl:value-of  select=”location”  /></location>

<!-- Perform a loop for each student in the training class --> <xsl:for-each select=”student”

<employee>

<name>

<first><xsl:value-of select=”first_name”/></first> <last><xsl:value-of select=”last_name”/></last>

</name>

<email><xsl:value-of select=”email”/></email> </employee>

</xsl:for-each>

</employeelist>

</xsl:template>

</xsl:stylesheet>

Using the XSLT Processor

So far in this chapter, we’ve used client-side and server-side techniques for XSLT pro-cessing. The client-side technique utilized a Web browser that has support for XSLT. The server-side technique leveraged server scripts developed in JSP and ASP. The JSP exam-ples used a JSP custom tag for the XSLT processing, whereas the ASP examples lever-aged the Microsoft XML server object.

For most B2B applications, the source XML document is retrieved by another applica-tion. This may be a standalone application or a component of a larger B2B application. In the case of a standalone application, the necessary code to perform the XSLT process-ing needs to be developed. For example, a Visual Basic or Visual C++ application can use the XSLT processor available with the Microsoft XML API. In a similar fashion, a Java application can use the XSLT processor available with the Apache Xalan API. The Apache Xalan API is available at http://xml.apache.org.

Here’s the code for a standalone Java application that uses the Apache Xalan API (note that the application accepts three command-line arguments—one each for the input XML document, the XSL style sheet, and the name of the output file):

java  XslTester  <input  XML>  <input  XSL>  <output  file>

The input XML document and the input XSL style sheet can be referenced using file-names or URLs. Listing 9.14 contains the complete code for XslTester.java.

LISTING 9.14  <install_dir>\ch9_xsl\b2b\XslTester.java

import  org.apache.xalan.xslt.*;

/**

* Usage: java XslTester <input XML> <input XSL> <output file> */

public  class  XslTester{

public  static  void  main(String[]  args)  {

try  {

// Verify the correct arguments are passed in if (args.length != 3) {

System.out.println(“Usage: java XslTester <input XML> <input XSL> ➥ <output file>”);

System.exit(1);

}

System.out.println(“Processing:  “  +  args[0]  +  “  and  “  +  args[1]);

Step 1: Get a reference to the XSLT Processor XSLTProcessor myEngine = XSLTProcessorFactory.getProcessor();

         Step  2:   Get  the  XML  input  document

XSLTInputSource  xmlSource  =  new  XSLTInputSource(args[0]);

//  Step  3: Get  the  XSL  style  sheet

XSLTInputSource  xslStylesheet  =  new  XSLTInputSource(args[1]);

//  Step  4: Setup  the  output  target

XSLTResultTarget  xmlOutput  =  new  XSLTResultTarget(args[2]);

// Step 5: Now process it! myEngine.process(xmlSource, xslStylesheet, xmlOutput);

System.out.println(“Created => “ + args[2]); System.out.println(“Done!”);

}

catch (Exception exc) { exc.printStackTrace();

}

}

}

The first task of the main method is verifying the correct number of parameters. Next, the application retrieves a reference to the XSLT processing engine using the factory method XSLTProcessorFactory.getProcessor(). The application then retrieves the input XML document and XSL style sheet based on the first two command-line argu-ments. The result target for the XSLT translation is configured to use the filename sup-plied as the third command-line argument. Finally, the XSLT processing engine is invoked using the objects xmlSource, xslStylesheet, and xmlOutput.

Running the Example

This example requires the Java Development Kit version 1.3 or higher. Follow these steps to test it:

     Open an MS-DOS window.

     Move to the directory <install_dir>\ch9_xsl\b2b\.

     Set up the Java classpath by typing setpaths.

     Execute the application by typing the following:

java XslTester trainingclass.xml train2employee.xsl testoutput.xml

     View the testoutput.xml file in a text editor. Verify that your document resembles this:

<?xml version=”1.0” encoding=”UTF-8”?> <employeelist>

<course_title>J2EE Essentials</course_title> <course_date start=”24 Sep 2001” end=”28 Sep 2001”/> <location>Philadelphia, PA</location>

<employee>

<name>

<first>Riley</first>

<last>Scott</last>

</name>

<email>riley@acmesoft.web</email>

</employee>

<employee>

<name>

<first>Torrance</first>

<last>Lee</last>

</name>

<email>torrance.lee@acmesoft.web</email>

</employee>

</employeelist>

The trainingclass.xml document is also available on the Web server at http:// localhost:8080/bookch9/hotshot/trainingclass.xml. The XslTester application also supports a URL for the XML document and XSL style sheet. You can access the trainingclass.xml document via the Web server by simply supplying the following URL:

java  XslTester  http://localhost:8080/bookch9/hotshot/trainingclass.xml

train2employee.xsl  testoutput.xml

This example demonstrates the technique used to retrieve an XML document and per-form the XSLT conversion. Once the XML data is converted to the desired XML output, the application can process it accordingly. For example, the application can use the SAX and DOM APIs to parse the XML document and store the results in a database. By lever-aging the SAX and DOM APIs, the application is very flexible in how it processes/stores the converted XML document.