Strange noclassdefnotfounderror with custom classloader

Berlin Brown <>
Sat, 20 Jun 2009 06:44:26 -0700 (PDT)
I know the complexities of classloading are difficult and I probably
need more logic here.

My goal was to have one jar and then have a user double click on the
jar in windows and have logic to load all the other dependent jars
using java code, custom loader. I had several reasons to do this.

There are several other jars and you can see the list here:

 public static final String [] JAVA_LIBRARIES = {

My classloader code is based on jetty's classloader and it works OK
but I keep get ting classnotdef errors. Strange ones. I can see a
clear distinction between classnotfound errors. If the file path to
the jar is invalid then I get classnotfound, easy to detect and fix.

Here is essentially the classloader code for future reference.

Classpath classpath = new Classpath();

boolean res = classpath.addComponent(libFilePath);

/// Classloader

private class Loader extends URLClassLoader {
        String name;
        Loader(URL[] urls, ClassLoader parent) {
            super(urls, parent);
            name = "StartLoader" + Arrays.asList(urls);

        public String toString() {
            return name;

//// Then set the classloader
//// where the URLs are the JAR libraries:
   URL [] urls = new URL[NUMBER_OF_JARS];
   for (x in urls) {
      urls[i] = new URL("THE JAR PATH");

    ClassLoader parent = Thread.currentThread().getContextClassLoader

        if (parent == null) {
            parent = Classpath.class.getClassLoader();
        if (parent == null) {

            parent = ClassLoader.getSystemClassLoader();
        return new Loader(urls, parent);


The code works fine but I can't explain for when I get classpath
loader issues. I have one theory one issue.

    [java] Exception in thread "main" java.lang.NoClassDefFoundError:
    [java] at java.lang.ClassLoader.defineClass1(Native Method)
    [java] at java.lang.ClassLoader.defineClass(
    [java] at
    [java] at
    [java] at$100
    [java] at$
    [java] at
    [java] at
    [java] at java.lang.ClassLoader.loadClass(
    [java] at sun.misc.Launcher$AppClassLoader.loadClass

    [java] at java.lang.ClassLoader.loadClass(
    [java] at java.lang.ClassLoader.loadClass(
    [java] at java.lang.ClassLoader.loadClassInternal

    [java] at java.lang.Class.getDeclaredFields0(Native Method)
    [java] at java.lang.Class.privateGetDeclaredFields(
    [java] at java.lang.Class.getDeclaredField(

I believe I Get this errror because there are multiple "classes" on
the same name in the classpath from two different jars and I guess the
classloader is confused?

other than that, i get other errors as well but can't pinpoint how I
get them.

Do you know how to diagnose these problems, should I build a more
robust classloader.

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