Pretty Print XML with Saxon: A Comprehensive Guide

Working with XML can be a real challenge, especially when it comes to formatting and readability. XML files can quickly become a jumbled mess of tags and attributes, making it difficult to understand and work with. That’s where pretty printing comes in – a process that formats XML files in a more human-readable way. In this article, we’ll explore how to pretty print XML with Saxon, a powerful and widely-used XSLT processor.

What is Pretty Printing?

Pretty printing is the process of formatting XML files to make them more readable and easier to understand. This involves indenting, adding whitespace, and breaking up long lines to create a more organized and structured layout. By pretty printing XML files, developers and users can more easily analyze, debug, and work with the data.

Why Use Saxon for Pretty Printing?

Saxon is an excellent choice for pretty printing XML files due to its powerful XSLT processing capabilities. Saxon is a widely-used, open-source XSLT processor that supports a range of features, including XSLT 3.0, XPath 3.0, and XQuery 3.0. With Saxon, you can create complex transformations and formatting rules to pretty print your XML files.

Preparing Your XML File

Before you can pretty print your XML file with Saxon, you need to ensure it’s well-formed and valid. Here are a few steps to prepare your XML file:

1. Check for syntax errors: Make sure your XML file is free from syntax errors, such as mismatched tags or invalid characters.
2. Validate your XML: Use an XML validator, such as XMLSpy or Oxygen XML, to ensure your XML file conforms to its specified schema or DTD.
3. Save your XML file: Save your XML file with a .xml extension and encode it in UTF-8.

Using Saxon for Pretty Printing

To pretty print your XML file with Saxon, you’ll need to create an XSLT stylesheet that defines the formatting rules. Here’s a step-by-step guide:

Step 1: Create an XSLT Stylesheet

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  exclude-result-prefixes="#all"
  version="3.0">

  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/*">
    <xsl:copy>
      <xsl:apply-templates/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="*|@*|comment()|processing-instruction()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>

</xsl:stylesheet>

This XSLT stylesheet defines a simple identity transform that copies the input XML file to the output, while applying the `indent=”yes”` attribute to pretty print the XML.

Step 2: Run Saxon from the Command Line

To run Saxon from the command line, you’ll need to download and install the Saxon HE (Home Edition) Java library. Once installed, you can use the following command:

[code]
java net.sf.saxon.Transform -s:input.xml -xsl:stylesheet.xsl -o:output.xml
[/code]

This command runs the Saxon Transformer, specifying the input XML file (`input.xml`), the XSLT stylesheet (`stylesheet.xsl`), and the output XML file (`output.xml`).

Step 3: Run Saxon from Your Java Application

If you prefer to integrate Saxon into your Java application, you can use the following code:

import net.sf.saxon.s9api.*;

public class PrettyPrintXML {
  public static void main(String[] args) throws SaxonApiException {
    Processor processor = new Processor(false);
    XsltCompiler compiler = processor.newXsltCompiler();
    XsltExecutable executable = compiler.compileSource(new StreamSource("stylesheet.xsl"));
    XsltTransformer transformer = executable.load();
    transformer.setSource(new StreamSource("input.xml"));
    Serializer serialize = new Serializer();
    serialize.setOutputWriter(new FileWriter("output.xml"));
    transformer.setDestination(serialize);
    transformer.transform();
  }
}

This code creates a Saxon processor, compiles the XSLT stylesheet, and transforms the input XML file to the output XML file.

Advanced Pretty Printing Techniques

While the basic XSLT stylesheet provided earlier will pretty print your XML file, you may want to apply more advanced formatting rules. Here are a few techniques to consider:

Using xsl:strip-space and xsl:preserve-space

To control whitespace in your XML file, you can use the `xsl:strip-space` and `xsl:preserve-space` elements. For example:

<xsl:strip-space elements="*"/>
<xsl:preserve-space elements="pre"/>

This code strips whitespace from all elements, except for the `pre` element, which preserves its whitespace.

Using xsl:value-of with disable-output-escaping

To preserve special characters in your XML file, such as `<` and `>`, you can use the `xsl:value-of` element with the `disable-output-escaping` attribute:

<xsl:value-of select="." disable-output-escaping="yes"/>

This code outputs the value of the current node, disabling output escaping to preserve special characters.

Using xsl:character-map

To replace special characters in your XML file, you can use the `xsl:character-map` element:

<xsl:character-map name="replace-ampersand">
  <xsl:output-character character="&" string="&amp;"/>
</xsl:character-map>

This code defines a character map that replaces the `&` character with the entity reference `&`. You can then use this character map in your XSLT stylesheet:

<xsl:output use-character-maps="replace-ampersand"/>

Conclusion

Pretty printing XML files with Saxon is a straightforward process that can greatly improve the readability and usability of your XML data. By following the steps outlined in this article, you can create a well-formatted XML file that’s easy to analyze and work with. Remember to experiment with advanced pretty printing techniques to customize the formatting of your XML file to your specific needs.

Tools and Resources
Saxon HE (Home Edition)	https://sourceforge.net/projects/saxon/
XMLSpy	https://www.altova.com/xmlspy
Oxygen XML	https://www.oxygenxml.com/

By now, you should have a solid understanding of how to pretty print XML files with Saxon. Remember to explore the advanced pretty printing techniques outlined in this article to take your XML formatting to the next level.

Frequently Asked Question

Get ready to transform your XML files into a work of art with Saxon! Here are the top 5 FAQs to help you pretty print your XML files with ease.