LoadClass throws a NoClassDefFoundError caused by a ClassNotFoundException

Question

Using the following code, I get a NoClassDefFoundError caused by a ClassNotFoundException:

File file = new File( "C:\\prototype.core.bl.xmodelval.xmodel-1.0.0.jar" ); URL url = file.toURI().toURL(); URL[] urls = new URL[] { url }; ClassLoader cl = new URLClassLoader( urls ); Class cls = cl.loadClass("de.zeb.control.prototype.core.bl.xmodelval.xmodel.entity.EntityNameLengthXModelValidationRule" ); 

Bank and class at the bank are definitely available. The following exception is thrown by cl.loadClass. Full exception stack trace:

 Exception in thread "main" java.lang.NoClassDefFoundError: de/zeb/control/prototype/core/bl/xmodelval/XModelValidationRule at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631) at java.lang.ClassLoader.defineClass(ClassLoader.java:615) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) at java.net.URLClassLoader.defineClass(URLClassLoader.java:283) at java.net.URLClassLoader.access$000(URLClassLoader.java:58) at java.net.URLClassLoader$1.run(URLClassLoader.java:197) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631) at java.lang.ClassLoader.defineClass(ClassLoader.java:615) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) at java.net.URLClassLoader.defineClass(URLClassLoader.java:283) at java.net.URLClassLoader.access$000(URLClassLoader.java:58) at java.net.URLClassLoader$1.run(URLClassLoader.java:197) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) at de.zeb.control.prototype.core.bl.xmodelval.jarwelfare.loader.XModelJarLoader.load(XModelJarLoader.java:32) at de.zeb.control.prototype.core.bl.xmodelval.jarwelfare.supplier.Runner.main(Runner.java:29) Caused by: java.lang.ClassNotFoundException: de.zeb.control.prototype.core.bl.xmodelval.XModelValidationRule at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) ... 24 more 

It seems strange to me that the full name of the ClassNotFoundException class does not match the name cl.loadClass.

Thank you for your help.

Answer 1

You may need to provide a parent class loader, because otherwise the class loader you specified will not be able to access any classes already present in your application. For instance:.

  ClassLoader cl = new URLClassLoader( urls , getClass().getClassLoader());