What You Need to Know About Whitespace in XML

  <Author> <FirstName>John</FirstName> <LastName>Smith</LastName> </Author> 

Here's a more complete example (see Example 1 in sample code): Let's assume that you want to get the first child element of <Author> using the DOM APIs as follows:

  XMLDocument doc = parser.getDocument(); Element elem = doc.getDocumentElement(); Node node = elem.getFirstChild(); 

With the default setting of the Oracle XDK DOM parser, the first document returns <FirstName> while the second document returns a text node that is a whitespace node!

Similarly, sometimes the XSLT transformation doesn't generate the results you expected. (See Example 2.) An XML document needs to be transformed using XSLT. The XSL stylesheet uses the position() function to create the ordering information for <Chapter> and <Section> elements:

  <?xml version="1.0"?> <Book> <Chapter> <Section/> <Section/> <Section/> </Chapter> <Chapter> <Section/> <Section/> <Section/> </Chapter> </Book> 

However, the following XSL stylesheet:

  <?xml version="1.0"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="xml" indent="yes"/> <xsl:template match="*"> <xsl:element name="{local-name()}"> <xsl:attribute name="Position"> <xsl:value-of select="position()"/> </xsl:attribute> <xsl:apply-templates select="@*|node()"/> </xsl:element> </xsl:template> </xsl:stylesheet> 

doesn't work that well; it creates the following result:

  <?xml version = '1.0' encoding = 'UTF-8'?> <Book Position="1"> <Chapter Position="2"> <Section Position="2"/> <Section Position="4"/> <Section Position="6"/> </Chapter> <Chapter Position="4"> <Section Position="2"/> <Section Position="4"/> <Section Position="6"/> </Chapter> </Book> 

The Positions are incorrect because of the whitespaces. If you remove whitespaces before calling the position() function in XSLT transformation, using the following stylesheet:

  <?xml version = '1.0' encoding = 'UTF-8'?> <Book Position="1"> <Chapter Position="2"> <Section Position="2"/> <Section Position="4"/> <Section Position="6"/> </Chapter> <Chapter Position="4"> <Section Position="2"/> <Section Position="4"/> <Section Position="6"/> </Chapter> </Book> 

The result would be what you expect:

  <?xml version = '1.0' encoding = 'UTF-8'?> <Book Position="1"> <Chapter Position="1"> <Section Position="1"/> <Section Position="2"/> <Section Position="3"/> </Chapter> <Chapter Position="2"> <Section Position="1"/> <Section Position="2"/> <Section Position="3"/> </Chapter> </Book> 

For this example, if you don't want to strip out the whitespaces for all XML elements, you can instead use <xsl:strip-space element="Book,Chapter, Section"> instead.

In the following sections, you will learn about the concept of XML whitespace along with tips to avoid such problems.

What is XML Whitespace?

XML considers four characters to be whitespace: the carriage return (\r or ch(13)), the linefeed (\n or ch(10)), the tab(\t), and the spacebar (' '). In XML documents, there are two types of whitespace:

• Significant whitespace is part of the document content and should be preserved.
• Insignificant whitespace is used when editing XML documents for readability. These whitespaces are typically not intended for inclusion in the delivery of the document.

Usually without DTD or XML schema definition, all whitespaces are significant whitespaces and should be preserved. However, with DTD or XML schema definitions, only the whitespaces in the content are significant as follows:

  <sig> ------------------ John Smith Product Manager Example.com -------------------- </sig> 

How XML Processors Handle XML Whitespace

XML standards specify how XML processors should handle the whitespace.

XML Parsing: The XML spec provides a built-in attribute xml:space to tell the XML parser whether it should ignore the whitespace characters. This attribute is inherited by child elements from their root element. When declared, it must be given as an enumerated type whose only possible values are " default" and "preserve". If " preserve" is specified, the whitespace within the defined element must be preserved.

Based on the W3C XML specification, the Oracle XML Developer's Kit (XDK) XML parsers, by default, preserves all whitespace. Therefore, the xml:space =" default " or xml:space =" preserve " will have the same result: The whitespace is preserved. To avoid preserving whitespace, you need to set Oracle XDK parsers as follows:

XDK DOM Parser:

  DOMParser parser = new DOMParser(); parser.setPreserveWhitespace(false); 

SAX Parser:

  SAXParser parser = new SAXParser(); parser.setPreserveWhitespace(false); 

XSLT Transformation. W3C XSLT specification provides two elements — xsl:strip-space and xsl:preserve-space— to handling whitespaces. The xsl:strip-space specifies the XML elements that should have whitespace text nodes (that is, text nodes composed entirely of whitespace characters) stripped. Note that the xsl:strip-space only affects nodes that are pure whitespace. xsl:strip-space can list as a set of element separated by whitespaces or use wildcards such as *. The xsl:preserve-space has similar syntax but does just the opposite to the xsl:strip-space .

The following example (see Example 3) applies an XSL stylesheet that copies the source document, except that the whitespace text nodes are stripped:

  <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:output method="xml" omit-xml-declaration="yes"/> <xsl:strip-space elements="*"/> <xsl:template match="@*|node()"> <xsl:copy> <xsl:apply-templates select="@*|node()"/> </xsl:copy> </xsl:template> </xsl:stylesheet> 

  <rootElement> <childElement test="true"> Value </childElement>This is the test <childElement test="true" xml:space="preserve"> Value </childElement> <childElement xml:space="preserve"> </childElement> <childElement> </childElement> </rootElement> 

  <rootElement><childElement test="true"> Value </childElement>This is the test <childElement test="true" xml:space="preserve"> Value </childElement><childElement xml:space="preserve"> </childElement><childElement/></rootElement> 

  import oracle.xml.parser.v2.XMLPrintDriver; import oracle.xml.parser.v2.XMLOutputStream; class MyXMLPrintDriver extends XMLPrintDriver { public MyXMLPrintDriver(java.io.OutputStream A) { super(A); out.setOutputStyle(XMLOutputStream.COMPACT); } } 

  XMLPrintDriver myprint = new XMLPrintDriver(System.out); myprint.setFormatPrettyPrint(false); Xml_doc.print(myprint); 

Jinyu Wang ( jinyu.wang@oracle.com ) is a senior product manager for Oracle XML and an XML evangelist. She is a co-author ofOracle Database 10g XML & SQL (Oracle Press).