Exception in thread "main" java.lang.NoClassDefFoundError: org/jaxen/NamespaceContext

使用dom4j的xpath查询节点，报如下错误：

Exception in thread "main" java.lang.NoClassDefFoundError: org/jaxen/NamespaceContext
    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 com.flfg.js.js.server.FLFGServiceLauncher.main(FLFGServiceLauncher.java:22)
Caused by: java.lang.ClassNotFoundException: org.jaxen.NamespaceContext
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    ... 4 more

需要在项目中添加jaxen包。