[英]ClassCastException thrown when calling .asSubclass from separate jar
I have a program through which I have the following three classes. 我有一个程序,通过它我有以下三个类。 These first two are in
jar1.jar
: 前两个是在
jar1.jar
:
Main
(uses the jar loading trick found here ): Main
(使用此处的jar加载技巧):
package prob1;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
public class Main {
static List<Class<?>> classes = new ArrayList<Class<?>>();
static String pathToJar = "/Users/vtcakavsmoace/Desktop/jar2.jar";
public static void main(String[] args) throws ClassNotFoundException, IOException, InstantiationException, IllegalAccessException {
loadJar();
classes.get(0).asSubclass(A.class).newInstance().someMethod();
}
private static void loadJar() throws IOException, ClassNotFoundException {
JarFile jarFile = new JarFile(pathToJar);
Enumeration<JarEntry> e = jarFile.entries();
URL[] urls = { new URL("jar:file:" + pathToJar + "!/") };
URLClassLoader cl = URLClassLoader.newInstance(urls);
while (e.hasMoreElements()) {
JarEntry je = e.nextElement();
if (je.isDirectory() || !je.getName().endsWith(".class")) {
continue;
}
String className = je.getName().substring(0, je.getName().length() - 6);
className = className.replace('/', '.');
classes.add(cl.loadClass(className));
}
jarFile.close();
}
}
A
: A
:
package prob1;
public interface A {
void someMethod();
}
And a second class found in jar2.jar
, B
: 在
jar2.jar
找到第二个类, B
:
package prob2;
import prob1.A;
public class B implements A {
@Override
public void someMethod() {
System.out.println("Hello, world!");
}
}
As you can see, class B
obviously implements interface A
. 如您所见,
B
类显然实现了接口A
However, when loading class B
, and then attempting to call asSubclass
on it, fails with the following exception: 但是,当加载类
B
,然后尝试在其上调用asSubclass
时,将失败并出现以下异常:
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.eclipse.jdt.internal.jarinjarloader.JarRsrcLoader.main(JarRsrcLoader.java:58)
Caused by: java.lang.ClassCastException: class prob2.B
at java.lang.Class.asSubclass(Class.java:3404)
at prob1.Main.main(Main.java:20)
... 5 more
Note that this does not fail when run through Eclipse. 请注意,在Eclipse中运行时不会失败。
What am I doing wrong here? 我在这做错了什么? How can I fix this?
我怎样才能解决这个问题?
Okay, found the answer using the knowledge that Erwin Bolwidt gave me; 好的,根据Erwin Bolwidt给我的知识找到答案; in class
Main
, replacing: 在
Main
类中,替换:
URLClassLoader cl = URLClassLoader.newInstance(urls);
with: 有:
URLClassLoader cl = URLClassLoader.newInstance(urls, Main.class.getClassLoader());
Fixes the problem. 解决了这个问题。 :P
:P
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