Using Xpath in Dom4j

Question

I get the following exception when trying to access any nodes of a parsed xml document on dom4j:

Exception in thread "main" java.lang.NoClassDefFoundError: org/jaxen/JaxenException at org.dom4j.DocumentFactory.createXPath(DocumentFactory.java:230) at org.dom4j.tree.AbstractNode.createXPath(AbstractNode.java:207) at org.dom4j.tree.AbstractNode.selectNodes(AbstractNode.java:164) at xmlparser.LevelsExtractor.findI(LevelsExtractor.java:73) at xmlparser.Main.main(Main.java:33)

I know that the parsing works, because I can have the parser print out the xml document or save it to file. Here is the code I'm using.

To parse the document:

 public class Parser {

 public Document parseWithSAX(File aFile) throws DocumentException {
    SAXReader xmlReader = new SAXReader();
    Document doc = xmlReader.read(aFile);
    return doc;
  }

To try to get a node I've tried the following lines, all of which produce the same error:

      List list = doc.selectNodes("");
      QName qn = new QName("////Token/text()='Introduction'");
      Element el = doc.selectSingleNode("////Token/text()='Introduction'");
      Node node = doc.selectSingleNode( "/DOCUMENT/PAGE/TEXT/TOKEN/text()= 'Introduction'");

This will print out the xml doc which I assume means that doc (which is the parsed xml doc) contains what it should.

      System.out.println(doc.asXML());

I really appreciate your help!

Answer 1

You should add jaxen library to your class path.

EDIT: Actually original dom4j distribution contains jaxen.jar in that as well as all other dependencies.

Answer 2

A java.lang.NoClassDefFoundError is thrown by the JVM when a dependency that was available at the time a particular class was compiled cannot be found on the classpath when the class is loaded for use by the JVM.

How are you invoking the parser code? Check and make sure that all the DOM4J dependencies in the lib folder of the DOM4J distribution (jaxen, jaxme-api etc) are on the classpath.

If you are invoking the parser from the command line you can use the -classpath option:

java -classpath C:\myjars\jar1.jar;C:\myjars\jar1.jar

If you are invoking the parser from Ant for example use the <classpath> tag:

<classpath>  
    <pathelement path="C:\myjars\jar1.jar"/>  
    <pathelement path="C:\myjars\jar2.jar"/>
</classpath>

Your xpath expressions are not even being evaluated so you should stoptweaking those until you have sorted out your classpath issues.

Answer 3

So xpath works if I include jaxen-1.1-beta-6.jar in addition to the jdom4 jar. Note the jaxen-1.1.1.jar does not work. If you have a classdef error from jdom look at their dependencies and make sure you are using their approved jars, (which for the 1.6.1 version is now often an older release of the jar). Hope this helps anyone with a similar problem. Thanks again for everyone's help!