Load a class for reflection when it's already loaded from elsewhere in java

I'm trying to write a decompiler for Java using reflection (all I need is the method signature information from a jar file passed in). I'm using a URLClassLoader to load classes from the jar file, and then pass that class on to my decompiler.

However, I've run into a problem. The jar I'm trying to read contains different versions of classes already loaded into my environment. So when I call

ClassLoader myClassLoader = URLClassLoader.newInstance(jars, null);
Class<?> classToDecompile = Class.forName(className, false, myClassLoader);

It returns not the class from my jar file, but the one that'开发者_如何学Pythons already been loaded. Is there a way to load the class information for reflection only and get it from the jar passed in rather than from the JRE?

Edit:

The jar I'm trying to decompile contains classes in the java.lang package, which causes a security exception to be thrown:

java.lang.SecurityException: Prohibited package name: java.lang

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ClassLoader.loadClass(String, boolean) - which URLClassLoader inherits - first checks for a previously-loaded class, and then, not finding any, checks with the parent class loader. You could override that method to bypass the check for a previously-loaded class. Not sure if you'd have to bypass the parent.

Mind you, this would be an evil class loader; you probably shouldn't use it for anything else.

You might also try reading the jar yourself, getting the contents of the class file (the byte codes), and calling ClassLoader.defineClass(name, byte[], int, int) yourself, supplying a unique name for the class. I think that's a better idea, actually.

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Why wasting time when there is JAD? If you still want to achieve that you have to write your own class loader with child-first strategy.