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Groups > comp.lang.java.programmer > #29496

Re: dealing with ClassLoaders...

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Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> wrote:
> Martin Gregorie <martin@address-in-sig.invalid> wrote:
>> public class MAClassLoader extends ClassLoader
>> {
>   [ no snip ]
>> }
>> I hope this is useful info.

On further examination, I think it isn't as simple as that.
Essentially, this "empty" ClassLoader-subclass would pass 
everything through to the parent classloader (or the pre-
mordial one, absent a parent) and thus not be associated to
any of the classes loaded through it, thus provide no
isolation at all.

My approach now is to override loadClass(String,boolean):

   @Override // ClassLoader
   public Class<?> loadClass( String name, boolean resolve)
      throws ClassNotFoundException
   {
      Class<?> res = null;
      if (name != null && name.startsWith(PACKAGE_PREFIX)) {
         synchronized (this) {
            res = m_classes.get(name);
            if (res != null) { return res; }
            byte[] classData = null; // TODO: get class data
            res = defineClass(name,classData, 0, classData.length);
            m_classes.put(name, res);
         }
      } else { 
         // if this fails, then so be it:
         res = super.findSystemClass(name);
      }
      if (resolve && res != null) { resolveClass(res); }
      return res;
   }
   // m_classes is Map<String,Class<?>> initialized to new HashMap<>()

The hole that remains is at the TODO marker in the code snippet.
I'd like to use system code to pull the byte[] or ByteBuffer out
of whatever jar-file or unpacked directory the whole app is deployed
to.

The then-branch of the big "if" is to solve a should-be-simple task:
Use the system class loader's code to locate the class, but let "this"
classloader end up being associated with it.

How can I do that?

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Thread

dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-07-31 19:40 +0000
  Re: dealing with ClassLoaders... Martin Gregorie <martin@address-in-sig.invalid> - 2014-07-31 20:44 +0000
    Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-01 14:22 +0000
      Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-01 21:10 +0000
        Re: dealing with ClassLoaders... Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-08-01 17:32 -0400
          Re: dealing with ClassLoaders... Joerg Meier <joergmmeier@arcor.de> - 2014-08-02 01:21 +0200
          Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-02 00:00 +0000
        Re: dealing with ClassLoaders... Martin Gregorie <martin@address-in-sig.invalid> - 2014-08-01 21:45 +0000
          Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-01 23:14 +0000
            Re: dealing with ClassLoaders... Martin Gregorie <martin@address-in-sig.invalid> - 2014-08-02 00:35 +0000
              Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-05 15:38 +0000
  Re: dealing with ClassLoaders... Silvio <silvio@internet.com> - 2014-08-01 13:31 +0200
    Re: dealing with ClassLoaders... Silvio <silvio@internet.com> - 2014-08-01 13:37 +0200
      Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-01 16:06 +0000
  Re: dealing with ClassLoaders... "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2014-08-01 13:19 +0100
    Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-01 15:51 +0000
  Re: dealing with ClassLoaders... Josip Almasi <joe@vrspace.org> - 2014-08-01 15:55 +0200
    Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-04 15:12 +0000
      Re: dealing with ClassLoaders... Mike Amling <mamling@chaff.us> - 2014-08-04 19:53 -0500
        Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-05 15:16 +0000
      Re: dealing with ClassLoaders... Josip Almasi <joe@vrspace.org> - 2014-08-08 11:53 +0200
        Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-08 18:46 +0000
          Re: dealing with ClassLoaders... Josip Almasi <joe@vrspace.org> - 2014-08-10 13:22 +0200
            Re: dealing with ClassLoaders... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-08-12 17:16 +0000

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