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Frequently asked questions
Apache Foundation Xalan Project Xerces Project Web Consortium Oasis Open


General XSLT

  1. Where do I go to learn about XSLT
  2. Where can I ask questions about XSLT
  3. TrAX and JAXP


  1. Determining Xalan-Java Version
  2. Determining the Serializer Version
  3. Which version of Xerces should I be using?
  4. Compatibility with Xalan-Java version 1
  5. Issues running Xalan-Java on JDK 1.3
  6. Issues running Xalan-Java on JDK/JRE 1.4 or higher
  7. Issues running Xalan-Java on Tomcat with JDK 1.4
  8. Issues running Applets with XSLTC in Web Browsers with JAVA Plug-in (JRE 1.4)
  9. Using the 'signature' file to verify a download

Performance Issues

  1. Speeding up transformations
  2. JAXP factory lookup procedure

Namespace Related

  1. Retrieving nodes in the default namespace
  2. Setting the parser to be namespace aware

Common Errors

  1. NoClassDefFound errors
  2. a "DOM006 Hierarchy request error"
  3. Namespace not supported by SAXParser
  4. Missing xsl:version attribute error
  5. StackOverflowError with recursive stylesheet
  6. OutOfMemoryError processing multiple documents
  7. File Not Found error
  8. No more DTM IDs are available
  9. IllegalAccessError or could not load on JDK 1.4


  1. Chaining transformations
  2. Stylesheet validation
  3. Setting output encoding
  4. Getting line and column numbers for errors in XML input documents and XSL stylesheets
  5. Servlet unable to find classes for extension functions/elements
  6. Translet name doesn't match stylesheet name


1. Where do I go to learn about XSLT

Where do I go to learn about XSLT?

The definitive sources are the W3C XSLT and XPath recommendations: XSL Transformations (XSLT) Version 1.0 and XML Path Language (XPath) Version 1.0.

For a brief listing of tutorials, discussion forums, and other materials, see Getting up to speed with XSLT.


2. Where can I ask questions about XSLT

Where can I ask questions about XSLT?

xalan-dev and xalan-j-users are for Xalan-Java questions only. This is not the best forum to ask general XSLT questions. The Mulberry XSL Mailing List is an excellent place to ask XSLT questions; please search XSL Frequently Asked Questions to ensure your question has not been already asked.


3. TrAX and JAXP

What are TrAX and JAXP, and are they related?

TrAX is the Transformation API for XML. In November 2000, TrAX was revised and incorporated into JAXP, the JAVA API for XML Processing. JAXP (including TrAX) provides users a standard, vendor-neutral API for working with (and transforming) XML documents. You can use this API to build applications that are not bound to the particular implementation details of a given XML parser or XSL transformer.

Xalan-Java includes the JAXP packages, implements the TrAX portion of that API (javax.xml.transform....), implements the XPath API of JAXP (javax.xml.xpath....), and includes xercesImpl.jar from Xerces-Java 2.11.0, which implements the parser portion of the API (javax.xml.parser....).

For more information, see Using the JAXP Transform APIs and Java API for XML Processing (JAXP) 1.3.


4. Determining Xalan-Java Version

How do I see what version of Xalan-Java I'm running? How do I determine which parser I'm using?

Using the EnvironmentCheck utility: To help diagnose classpath problems and also determine which version of Xalan-Java is being used, try running Xalan-Java's environment checking utility.

You can run this utility from the command line as follows:

java org.apache.xalan.xslt.EnvironmentCheck [-out outFile]

You can also call this utility from within your application. For example,

boolean environmentOK = (new EnvironmentCheck()).checkEnvironment (yourPrintWriter);

Be sure to run EnvironmentCheck in the environment where you are experiencing the problem. For example, if you get a NoClassDefFound error from a command-line application, run EnvironmentCheck on the command line with exactly the same classpath. If the error occurs inside your Java application (or in a servlet, etc.), be sure to call the EnvironmentCheck checkEnvironment(...) method from within your running application.

Best of all, you can call checkEnvironment from a stylesheet using extensions:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="" version="1.0"
<xsl:output indent="yes"/>

<xsl:template match="/">
    <xsl:copy-of select="xalan:checkEnvironment()"/>


5. Determining the Serializer Version

How do I see what version of the Serializer I'm running?

Xalan's serialier is now shared with Xerces. It may be packaged in Xalan, or Xerces, or in the JRE itself. You can run the serializer's Version utility from the command line as follows:

java org.apache.xml.serializer.Version

The output should indicate which serializer you are using.


6. Which version of Xerces should I be using?

Which version of Xerces-Java should I be using?

Xalan-Java Version 2.7.3 has been tested with Xerces-Java 2.12.2. See Status.


7. Compatibility with Xalan-Java version 1

How do I run applications that use the Xalan-Java version 1 API with Xalan-Java

The Xalan-Java version 1 compatibility API has been deprecated and removed, so you must use the Xalan-Java version 2 API. We strongly encourage you to use the Java API for XML Processing (JAXP) 1.3. For more information, see the FAQ on TrAX and JAXP.


8. Issues running Xalan-Java on JDK 1.3

I'm having a problem building or running Xalan-Java on the JDK 1.3.

The JDK 1.3 automatically places everything in the lib/ext directory in front of everything you place on the classpath. If this directory contains a version of DOM, JAXP, or Xerces that predates the Xalan-Java distribution you are using, you may have problems!

The IBM JDK 1.3 includes an earlier version of xerces.jar in the lib/ext directory, a version that does not implement the JAXP 1.3 interfaces and therefore does not work with the current Xalan-Java release. Accordingly, you must either remove the xerces.jar that is in that directory or replace it with the xercesImpl.jar that is included with the Xalan-Java distribution.

The SUN JDK 1.3 includes a pre-1.1 version of the JAXP in crimson.jar. Either remove the crimson.jar in that directory or overwrite it with a newer crimson.jar that includes and implements the JAXP 1.3 interfaces.


9. Issues running Xalan-Java on JDK/JRE 1.4 or higher

I'm having a problem running Xalan-Java on JDK/JRE 1.4 or higher

JDK/JRE 1.4, and JDK/JRE 5.0 is packaged with an old version of Xalan-Java. The JDK/JRE will attempt to use this version instead of any on the classpath. Unfortunately, this causes problems when attempting to use a newer version of Xalan-Java.

You can always determine which version of Xalan-Java you are running by using the EnvironmentCheck class or by using the xalan:checkEnvironment extension function. It is highly recommended that you use this method to verify the version of Xalan-Java you are running, especially before opening a bug report.

To use a newer version of Xalan-Java and override the one packaged with the JDK:

The following methods do not work:


10. Issues running Xalan-Java on Tomcat with JDK 1.4

I got java.lang.IllegalAccessError running Xalan-Java on Tomcat with JDK 1.4.

jakarta-tomcat 4.1.* is packed with an old version of xercesImpl.jar. Based on the Endorsed Standards Override Mechanism, you should replace it with the newer xercesImpl.jar. You should add a newer xalan.jar and serializer.jar to Tomcat as well. Read the FAQ about Issues running Xalan-Java on JDK/JRE 1.4 or higher. Place the xalan.jar, serializer.jar, and xercesImpl.jar in the <Tomcat_Home>\common\endorsed directory, where <Tomcat_Home> is where the Tomcat application server is installed.


11. Issues running Applets with XSLTC in Web Browsers with JAVA Plug-in (JRE 1.4)

I got javax.xml.transform.TransformerException running my applet which uses XSLTC in JRE 1.4.

To overwrite an older version of Xalan Java; packaged with JRE 1.4 or higher you can add a newer xalan.jar and serializer.jar to the <jre-home>\lib\endorsed directory. Read the FAQ about Issues running Xalan-Java on JDK/JRE 1.4 or higer. If there is a META-INF/services/javax.xml.transform.TransformerFactory file in xalan.jar (as there is in the Xalan Java distributions), then the TransformerFactoryImpl setting in this file will be used by the JVM during the factory finder lookup procedure. The TransformerFactoryImpl for the Xalan Java Interpretive processor is the default setting in the META-INF/services/javax.xml.transform.TransformerFactory file, therefore, you will get an error when your applet attempts to use the XSLTC implementation.

To work around this problem, you can change the contents of the META-INF/services/javax.xml.transform.TransformerFactory file in xalan.jar so that it refers to the transformer factory class implementation for XSLTC, org.apache.xalan.xsltc.trax.TransformerFactoryImpl.

Another solution is to create a jar that contains a META-INF/services/javax.xml.transform.TransformerFactory file containing the value org.apache.xalan.xsltc.trax.TransformerFactoryImpl. Place the jar in the <jre-home>\lib\endorsed directory. When you name your jar file, the ASCII code of the first character should be smaller than the ASCII code of "X" to ensure that your jar will be loaded before xalan.jar


12. Using the 'signature' file to verify a download

How do I use the "signature" file to verify my download?

For each Xalan-Java download file there is a corresponding signature file. The signature file for xalan-j_2_0_1.tar.gz, for example, is xalan-j_2_0_1.tar.gz.sig.

The .sig files are PGP signatures of the actual .zip or .tar.gz download files. You can use these files to verify the authenticity of the download. You do not need the .sig file to use the corresponding download file.

To check the authenticity of a Xalan-Java distribution, you need a copy of PGP which is available in a number of licenses, including some free non-commercial licenses, either from an site or on the site. Once you have a version of PGP installed, you should be able to 'verify the signature' of the .sig file, which basically verifies that the corresponding .zip or tar.gz file has not been changed since we signed it.

The PGP key may be found within the file KEYS.


13. Speeding up transformations

What can I do to speed up transformations?

In the ongoing development of Xalan-Java, enhancing performance is the primary goal of the Xalan-Java team. Here are some preliminary suggestions for you to keep in mind as you set up your applications:


14. JAXP factory lookup procedure

What is the JAXP factory lookup procedure and does it affect performance?

JAXP uses an ordered lookup procedure to find factory implementations, such as an implementation of javax.xml.transform.TransformerFactory. For information on this procedure, refer to Section 3 Plugability in JAXP 1.3.

In most cases, Factory classes need only be looked up once for an application, so performance is not an issue. However, there may be scenarios where the lookup procedure executes multiple times which could impact performance. In these cases, users may want to set system properties or populate the file in order to shorten the time spent in the lookup procedure.


15. Retrieving nodes in the default namespace

XPath isn't retrieving nodes that are in the default namespace I defined. How do I get them?

If you are looking for nodes in a namespace, the XPath expression must include a namespace prefix that you have mapped to the namespace with an xmlns declaration. If you have declared a default namespace, it does not have a prefix (see XPath Node Tests). In order to construct XPath expressions to retrieve nodes from this namespace, you must add a namespace declaration that provides a prefix you can include in the XPath expressions.

Suppose, for example, you you want to locate nodes in a default namespace declared as follows:

Add a namespace declaration with a prefix:

Then you can use foo: in your XPath expression.

Hint: Avoiding the use of default namespaces will prevent this problem from occuring.


16. Setting the parser to be namespace aware

How do I set my parser to be namespace aware?

If you use a TransformerFactory to process a stylesheet Source and generate a Transformer, the TransformerFactory instructs the SAXParserFactory to set the parser's namespaceAware property to true. But if you call the parser directly, you may need to set the namespaceAware property yourself. for example:

javax.xml.parsers.SAXParserFactory spFactory =
note For more information about setting the namespaceAware property, and SAX2 vs. JAXP default settings, see JAXP FAQ: Warning about namespace processing defaults.


17. NoClassDefFound errors

I'm getting a NoClassDefFound error. What has to be on the classpath?

  1. xalan.jar, serializer.jar, xml-apis.jar, and xercesImpl.jar -- or the XML parser you are using -- must always be on the classpath.

  2. To run the samples in the samples subdirectories, xalansamples.jar must be on the classpath. To run the servlet samples, you must place xalanservlet.war on a web server with a servlet engine and you must put the javax.servlet and javax.servlet.http packages on the classpath. These packages are available via the servlet.jar file found in Apache Tomcat ( see The Jakarta Site - Apache Tomcat ).

  3. To run extensions which use the component and script extension elements (including the samples in samples/extensions), bsf.jar must be on the classpath. To run extensions implemented in JavaScript, js.jar must also be on the classpath. For information on what you need to run extensions implemented in other scripting languages, see Supported languages.
You can check the correctness of your environment with the EnvironmentCheck feature.

For more information, see Setting up the system classpath.


18. a "DOM006 Hierarchy request error"

Why do I get a "DOM006 Hierarchy request error" when I try to transform into a DOM Document node?

This error occurs when Xalan-Java tries to add a Node to a Document node where it isn't allowed. For example, attempting to add non-whitespace text to the DOM Document node produces this error.

The error can also occur when a Document node is created with the DOMImplementation createDocument() method, which takes a qualified name as an argument and creates an element node. If you then pass the returned Document node to Xalan-Java, you get a "DOM006 Hierarchy request error" when Xalan-Java tries to add a second element to the Document node. The solution is to either use the DocumentBuilder newDocument() method to create a Document that does not contain an element node, or use a DocumentFragment. It should be noted that the DocumentBuilder newDocument() method is "Non-preferred" according to the JAXP 1.3 documentation.


19. Namespace not supported by SAXParser

Why am I getting a "Namespace not supported by SAXParser exception?

We have seen this problem arise for two quite different reasons:

SAX1 on the classpath

SAX1 should not be on your classpath. The SAX1 interfaces and implementations of the SAX1 SAX parser are not namespace aware.

To help diagnose your classpath, you can use the EnvironmentCheck utility. If you are running under JDK 1.3, see Issues running Xalan-Java on JDK 1.3. If you are running a servlet, make sure the webserver is not placing SAX1 on the classpath.

When you create a Transformer, you must use a namespace-aware parser to parse the stylesheet.


20. Missing xsl:version attribute error

I'm getting an error about my stylesheet missing the xsl:version attribute - what's wrong?

There are two common causes for this error.

  1. Using the wrong URI for the xsl: prefix will cause this message. URIs, and namespace URIs in particular, are case sensitive. Ensure the URI for the xsl namespace is "".

  2. The parser you are using to process a stylesheet Source and generate a Transformer does not have the namespaceAware property set to true.
    When you create a Transformer, you must use a namespace-aware parser to parse the stylesheet.


21. StackOverflowError with recursive stylesheet

Xalan-Java dies with a java.lang.StackOverflowError when I run a deeply recursive stylesheet. The same stylesheet worked fine in the past (or on other machines). What's happening?

That may not be our fault. As of JDK 1.3.x, many Java Virtual Machine publishers reduced the default size of a thread's call stack from 1MB to 256KB. This allows more threads to run simultaneously, but it means that each thread is more limited in how deeply its function calls can be nested.

Some JVMs may offer an option that allows you to raise this limit. For example, in Sun JDK 1.3.1 you can start JVM with the -Xss1m option to allow each thread to use a full megabyte. In IBM's JDK you can start with the -Xss1m and -Xoss1m options. Other JVMs may set this in other ways, or may not allow you to control it at all; check the documentation on your system for details.

Note too that on some platforms 1MB is an architectural upper limit on the stack size, so setting -Xss2m (or equivalent) may not allow deeper recursion than -Xss1m.


22. OutOfMemoryError processing multiple documents

I get a java.lang.OutOfMemoryError when I try to process multiple documents with the document() function. What can I do?

As a general rule, Xalan-Java currently caches all of the documents that you read in with the document() function during a transformation.

If your objective is to transform a series of documents, you can break the process into a series of transformations. The PipeDocument extension element provides one strategy for batching a series of parallel transformations.

Another alternative is to place your document() call in the select attribute of an xsl:for-each instruction element and use a custom PI (Processing Instruction) to turn off document caching. Include an XPath expression in your document() call if you do not need to process the entire document.

Sample stylesheet fragment:

<xsl:template match="doc">
  <xsl:for-each select="document(@href)/bar/zulu">
    <!-- process each document -->
note PIs do not ordinarily uses namespaces, so "xalan:" is a 'fake' namespace we have included to indicate that this is not a standard PI.

If you include an XPath expression in your document() call, you can also turn on incremental transform to eliminate the need to read in the entire document. In fact, you can take advantage of the incremental transform feature even if you are not turning off document caching.

You can also increase your JVM heap size with the -Xmx or -mx flag, depending on which JVM you are using (you can include both flags, and the JVM will ignore the one it doesn't understand). For example, to give your JVM 64 meg, try
java -Xmx64m -mx64m Class


23. File Not Found error

Why do I get 'file not found' when I pass c:\path\filename.txt?

Xalan-Java often requires legal URLs as system identifiers, not local pathnames (this is partly due to underlying parsers requiring this). A simple (but not always correct!) way to change a local pathname into a URL in Java 1.1x is:

  public static String filenameToURL(String filename)
    File f = new File(filename);
    String tmp = f.getAbsolutePath();
    if (File.separatorChar == '\\')
      tmp = tmp.replace('\\', '/');
    // Note: gives incorrect results when filename already begins with
    return "file:///" + tmp;

For a slightly more detailed example, see org.apache.xml.utils.SystemIDResolver.


24. No more DTM IDs are available

What does: "XSLT Error (javax.xml.transform.TransformerException): org.apache.xml.dtm.DTMException: No more DTM IDs are available" mean?

It means you are probably using a very old version of Xalan or Xalan-Java, likely the version 2.2D11 which was packaged in JDK1.4. Architectural changes made in early 2002 should have eliminated this issue for almost all cases.

You should verify the version of Xalan-Java you are using by running the EnvironmentCheck utility, and read the FAQ about Issues running Xalan-Java on JDK 1.4.


25. IllegalAccessError or could not load on JDK 1.4

Why do I get a "java.lang.IllegalAccessError" or the message "Could not load the property file ''" when I try to transform using XSLTC or Xalan-Java Interpretive?

These errors may occur if you use JDK 1.4 or later releases.

JRE 1.4 and later releases contain copies of Xalan-Java. In some cases, the JRE includes only Xalan-Java Interpretive, while in other cases it also includes XSLTC. Typically, the copy of the processor packaged with the JRE will be loaded in preference to any copy of Xalan-Java on your class path.

Beginning with Xalan-Java 2.5, Xalan-Java Interpretive and XSLTC are both packaged in xalan.jar, and share some of the same classes. If you are using a version of the JRE that contains Xalan-Java Interpretive, but not XSLTC, and you try to use XSLTC on your class path, classes from that version of XSLTC may be loaded along with classes from the version of Xalan-Java packaged with your JRE.

Because the classes may be from different versions of Xalan-Java, the results may be unpredictable. In particular, a java.lang.IllegalAccessError may be thrown, or an org.apache.xml.utils.WrappedRuntimeException containing the message: "Could not load the property file '' for output method 'xml' (check CLASSPATH)" may be thrown.

To work around those problems, please read the FAQ entitled Issues running Xalan-Java on JDK 1.4.


26. Chaining transformations

How do you chain together a series of transformations?

Xalan-Java supports two strategies for chaining together a series of transformations such that the output of each transformation provides input for the next transformation.

For the details and links to examples, see Using transformation output as input for another transformation.


27. Stylesheet validation

How do I validate an XSL stylesheet?

An XSL stylesheet is an XML document, so it can have a DOCTYPE and be subject to validation, right?

The XSLT Recommendation includes a DTD Fragment for XSL Stylesheets with some indications of what you need to do to create a complete DTD for a given stylesheet. Keep in mind that stylesheets can include literal result elements and produce output that is not valid XML.

You can use the xsl:stylesheet doctype defined in xsl-html40s.dtd for stylesheets that generate HTML.


28. Setting output encoding

Why is the output character encoding I set in the stylesheet not being used?

If you use a character output stream to instantiate the StreamResult object which holds the transformation output, the Writer uses its own encoding, not the encoding you specify in the stylesheet.

If you want to use the stylesheet output encoding, do not use StreamResult( to instantiate the holder for the output. Alternatively, you can specify the encoding when you create a Writer ( Once the Writer exists, you cannot change its encoding. If the transformation is run in a servlet, it is possible that the Writer is coming from the ServletResponse object.

If the stylesheet is run using the JAXP APIs and the Transformer's setOutputProperty() method is invoked, it is possible to set the "encoding" property and over-ride the value in the stylesheet.


29. Getting line and column numbers for errors in XML input documents and XSL stylesheets

How do I get line numbers for errors in the XML or XSL input when I am performing a transformation?

Use or mimic the command-line processor (org.apache.xalan.xslt.Process).

A TransformerException generally wraps another exception, often a SAXParseException. The command-line processor uses the static org.apache.xml.utils.DefaultErrorHandler printLocation() method to chase down the exception cause and get a SourceLocator that can usually report line and column number.

Suppose you wanted to modify the ValidateXMLInput sample in the samples/Validate subdirectory to include line and column numbers . All you need to do is call DefaultErrorHandler.printLocation() in the the Handler internal class error() and warning() methods. For example, replace

public void error (SAXParseException spe)
  throws SAXException
  System.out.println("SAXParseException error: " + spe.getMessage());


public void error (SAXParseException spe)
  throws SAXException
  PrintWriter pw = new PrintWriter(System.out, true);
  org.apache.xml.utils.DefaultErrorHandler.printLocation(pw, spe);
  pw.println("SAXParseException error: " + spe.getMessage());

You can also replicate code from the printLocation() method to obtain a SourceLocator, and then use the SourceLocator getLineNumber() and getColumnNumber() methods. The getRootSourceLocator() method below returns a SourceLocator.

import javax.xml.transform.SourceLocator;
import javax.xml.transform.TransformerException;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.apache.xml.utils.SAXSourceLocator;
import org.apache.xml.utils.WrappedRuntimeException;
public static SourceLocator getRootSourceLocator(Throwable exception)
  SourceLocator locator = null;
  Throwable cause = exception;
  // Try to find the locator closest to the cause.
    if(cause instanceof SAXParseException)
      locator = new SAXSourceLocator((SAXParseException)cause);
    else if (cause instanceof TransformerException)
      SourceLocator causeLocator = 
      if(null != causeLocator)
        locator = causeLocator;
    if(cause instanceof TransformerException)
      cause = ((TransformerException)cause).getCause();
    else if(cause instanceof WrappedRuntimeException)
      cause = ((WrappedRuntimeException)cause).getException();
    else if(cause instanceof SAXException)
      cause = ((SAXException)cause).getException();
      cause = null;
  while(null != cause);
  return locator;
note Xalan-Java exception handling: The exception architecture in Xalan-Java and with transforms in general is tricky because of multiple layers of exception handling, involving movement back and forth between SAX and Transformer exceptions and across pipes. Xalan-Java often uses a WrappedRuntimeException to throw over many layers of checked exceptions, in order not to have every possible checked exception be declared for every function in the stack, which means it has to catch this exception at the upper levels and unwrap the exception to pass it on as a TransformerException.

A JAXP 1.3 TransformerException often wraps another exception. Two of the TransformerException structures that are frequently used to construct contained exceptions in JAXP 1.3 do not set the locator. The locator is not set because we don't know the type of exception that the Throwable argument represents. The solution is to chase up the contained exceptions to find the root cause, which will usually have a location set for you. This can be somewhat tricky, as not all the exceptions may be TransformerExceptions. A good sample is in the DefaultHandler static printLocation() method, which the Xalan-Java command-line processor uses to report errors. You can also roll your own functions along the lines of the getRootSourceLocator() example above.


30. Servlet unable to find classes for extension functions/elements

My servlet cannot find classes that implement extension functions or elements. What can I do?

If you install xalan.jar in the webserver's lib directory (e.g., tomcat/lib), as opposed to the servlet application's lib directory, then the Xalan-Java classes are loaded by a classloader that does not see the classes in the application's classloader (i.e., the extension classes, if you placed them there). The Xalan-Java classes try to load the extension classes using their own classloader, and that attempt fails.

Workaround: place xalan.jar in the servlet application's lib directory and NOT in the webserver's lib directory. Another workaround is to place the extension classes also in the webserver's lib directory, but you generally want to avoid cluttering that directory.

Thanks to Gunnlauger Thor Briem ( for providing this information.


31. Translet name doesn't match stylesheet name

My stylesheet is named foo-bar.xsl, but XSLTC created a translet named foo_bar. Is that a bug?

No. The name of a translet is usually the name of the stylesheet, the name specified using the translet-name attribute on the XSLTC TransformerFactory or the name specified for the translet on the command-line invocation. However, the name of the translet is also the name of a Java class. Any character that is not permitted in a class name is replaced with an underscore.