Paul Moore Paul Moore - 8 months ago 41
Java Question

How do I diagnose Java ClassNotFound exception happening in scripting languages but not Java code

I am trying to use Joda Time in Java on Windows. I've downloaded Joda Time 1.2 and put the JAR on my CLASSPATH:

PS D:\Java\Jars> $env:CLASSPATH
.;C:\Program Files\Java\jre6\lib\ext\;D:\Java\Jars\joda-time-2.1.jar

The following Java code works perfectly:

import org.joda.time.*;

class Foo {
public static void main (String[] args) {
System.out.println("Hello, world");
DateTime d = new DateTime();
DateTime b = new DateTime(1981,12,25,0,0);
Period p = new Period(b,d);

However, when I try to import joda time from a scripting language, I get ClassNotFound errors.


PS D:\Java\Jars> java -jar .\jython.jar
Jython 2.5.2 (Release_2_5_2:7206, Mar 2 2011, 23:12:06)
[Java HotSpot(TM) Client VM (Sun Microsystems Inc.)] on java1.6.0_31
Type "help", "copyright", "credits" or "license" for more information.
>>> from org.joda.time import DateTime
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named joda
>>> import os
>>> os.getenv("CLASSPATH")
'.;C:\\Program Files\\Java\\jre6\\lib\\ext\\;D:\\Java\\Jars\\joda-time-2.1.jar'


PS D:\Java\Jars> java -jar .\clojure-1.4.0.jar
Clojure 1.4.0
user=> (import (org.joda.time DateTime Period))
ClassNotFoundException org.joda.time.DateTime$ (:-1)

How can I diagnose what is going wrong here? Presumably there is something specific to the scripting environments that is causing the issue. I know Python, but I'm not very familiar with the Java-interop aspects of Jython. I know little about Clojure beyond enough to set up the above test.

The classpath within Jython seems fine, as shown.


You are running both programs directly out of their JAR's:

java -jar archive.jar

Which does not use the system class path. An executable JAR must be bundled with all it's dependencies. Try this simple alternative for testing purposes:

java -cp "D:\Java\Jars\joda-time-2.1.jar;D:\Java\Jars\clojure-1.4.0.jar" clojure.main

Which will run the Clojure command line evaluator, with the Joda Time libraries included. Something similar should be available for Jython as well.