加载jar文件时找不到Java类

Question

I am working on a API system for a program. This system goes to a 'plugin' folder and loads every jar there. I am trying to load the main class of the jar file that is in the 'plugin' folder, but while doing so, I get a ClassNotFoundException.

Here is my code:

private static void loadClassFromJar(String PluginJar) throws MalformedURLException, ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {
    logger.debug("jar:file:" + "./debug/plugins/DiamondCorePlugin.jar!/");
    URL[] urls = { new URL("jar:file:" + FileList.PluginFolder.getAbsolutePath() + PluginJar +"!/") };
    URLClassLoader ClassLoader = URLClassLoader.newInstance(urls);
    Class<?> Class = ClassLoader.loadClass("net.trenterprises.diamondcore.plugin.Main");
    Object Object = Class.newInstance();
    Method EventMethod = Object.getClass().getMethod("onEnable");
    EventMethod.invoke(Object);
}

If the question is vague or unclear, please let me know (I am new around here, so I try my best to word any question I ask).

EDIT: Forgot to include the stack trace. Here it is!

java.lang.ClassNotFoundException: net.trenterprises.diamondcore.plugin.Main
at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.net.FactoryURLClassLoader.loadClass(URLClassLoader.java:798)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at net.trenterprises.diamondcore.cross.api.PluginLoader.loadClassFromJar(PluginLoader.java:53)
at net.trenterprises.diamondcore.cross.api.PluginLoader.loadAllPlugins(PluginLoader.java:25)
at net.trenterprises.diamondcore.DiamondCoreServer.<init>(DiamondCoreServer.java:47)
at net.trenterprises.diamondcore.run.main(run.java:15)

Answer 1

Either the jar does not contain the requested class (check with a zip-tool or jar -tf DiamondCorePlugin.jar , or the jar-URL is not correct (it seems to point to a resource inside the jar, not the jar itself). You can create it a little easier like:

File file = new File("debug/plugins/DiamondCorePlugin.jar");
URL[] urls = { file.getAbsoluteFile().toURI().toURL() };