java - loadClass 抛出由 ClassNotFoundException 引起的 NoClassDefFoundError

Question

使用以下代码，我得到由 ClassNotFoundException 引起的 NoClassDefFoundError:

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" );

jar 和 jar 中的类肯定可用。 cl.loadClass 引发以下异常。完整的异常堆栈跟踪如下:

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

对我来说，ClassNotFoundException 的完整类名与 cl.loadClass 的名称不匹配，这似乎很奇怪。

感谢您的帮助。

Answer 1

您可能需要提供父类加载器，否则您定义的类加载器将无法访问应用程序中已存在的任何类。例如:

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