What Version of Xerces are you Using?

XML developers often find themselves struggling with multiple versions of the Xerces parser for Java which support different, slightly incompatible versions of SAX, DOM, Schemas, and even XML itself. Xerces can be hiding in a number of different places including the classpath, the jre/lib/endorsed directory, and even the JDK itself. Here’s how you can find out which version you actually have.

First, from the command line, try this:

$ java -org.apache.xerces.impl.Version
Xerces-J 2.8.0

If that fails:

$ java  org.apache.xerces.impl.Version
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/xerces/impl/Version

Then point the classpath at the jar file you’re loading:

$ java -classpath dtd-xercesImpl.jar  org.apache.xerces.impl.Version
Xerces-J 2.8.0

If you don’t have a Xerces jar in your classpath, then if you’re using Java 5 or later, you likely have the version of Xerces bundled with the JDK. Check its version thusly:

$ java com.sun.org.apache.xerces.internal.impl.Version
Xerces-J 2.6.2

Finally, if you need to find out from within your source code, you invoke the static Version.getVersion() method like so:

String xercesVersion = Version.getVersion();

For comparisons–e.g. to see if you have Xerces version 2.6.1 or later–this simple bit of code will convert most version strings. including Xerces’s, to a decimal value:

    public static double toDouble(String s) {
        try {
            return Double.parseDouble(s);
        }
        catch (NumberFormatException ex) {
            s = removeExtraPeriods(s);
            return Double.parseDouble(s);
        }
    }

    private static String removeExtraPeriods(String s) {
        boolean decimalPointSeen = false;
        StringBuffer result = new StringBuffer(s.length());
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c >= '0' && c <= '9') result.append(c);
            else if (c == '.' && !decimalPointSeen) {
                result.append(c);
                decimalPointSeen = true;
            }
        }
        return result.toString();
    }

This covers most version string formats. I’ll leave it as an exercise for the reader to extend it to handle cases like comparing 2.6.2 to 2.6.2b.

Incidentally, the same tricks work for Xalan. You just have to point to org.apache.xalan.Version instead of org.apache.xerces.impl.Version:

$ java -classpath xalan.jar org.apache.xalan.Version
Xalan Java 2.7.0

This entry was posted on Monday, March 31st, 2008 at 9:52 am and is filed under XML. You can follow any responses to this entry through the Atom feed. Both comments and pings are currently closed.