[英]ClassCastException thrown when calling .asSubclass from separate jar
我有一個程序,通過它我有以下三個類。 前兩個是在jar1.jar
:
Main
(使用此處的jar加載技巧):
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
:
package prob1;
public interface A {
void someMethod();
}
在jar2.jar
找到第二個類, B
:
package prob2;
import prob1.A;
public class B implements A {
@Override
public void someMethod() {
System.out.println("Hello, world!");
}
}
如您所見, B
類顯然實現了接口A
但是,當加載類B
,然后嘗試在其上調用asSubclass
時,將失敗並出現以下異常:
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
請注意,在Eclipse中運行時不會失敗。
我在這做錯了什么? 我怎樣才能解決這個問題?
好的,根據Erwin Bolwidt給我的知識找到答案; 在Main
類中,替換:
URLClassLoader cl = URLClassLoader.newInstance(urls);
有:
URLClassLoader cl = URLClassLoader.newInstance(urls, Main.class.getClassLoader());
解決了這個問題。 :P
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