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Re: dealing with ClassLoaders...

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On 08/04/2014 05:12 PM, Andreas Leitgeb wrote:
> Josip Almasi <joe@vrspace.org> wrote:
>> On 07/31/2014 09:40 PM, Andreas Leitgeb wrote:
>>> The classloader tutorials I skimmed so far seem to imply, that
>>> a custom classloader is only appropriate to enable classloading
>>> from sources that the system classloader cannot handle itself.
>> Nah, it's also appropriate for context isolation.
>
> But it seems like it doesn't really make it easy to use it
> that way.

Noone said it's easy;)


>>> Is there a clean way to keep classes of a given package confined
>>> to some custom classloader, in order to control the classes' and
>>> their statics' scope/lifetime?
>> Yep, just don't break delegation model.
>> Model says something like, a classloader should ask parent classloader
>> if it has already loaded the class.
>> So, make sure you respect that rule.
>
> The twist in my case comes from the fact, that the parent *could*
> theoretically have loaded one of my special classes, but that would
> just indicate a programming error (aka Bug), so I'd rather have the
> compiler or at least the VM report a strange ClassCastException
> than silently use one of my classes loaded by wrong classloader.

Don't worry, it won't be silent:>
Mess up anything, and you get strange ClassCastExceptions.

>> Also, make sure your loaders don't load the same packages.
> This I don't understand.
> While my "special classes" happen to be in a specific package,
> I don't see, why packages as such would be relevant. I'd expect
> that even within the same package I should (in principle) be
> allowed to have some classes loaded through parent and others
> through custom classloader.

Well your classes 'happen' to be in specific packages, but I think you 
should use that to your advantage, to avoid confussion and classloader bugs.
It gets ugly when equals() starts throwing up.
Better have clearly divided responsibilities.

> I'd welcome hints for how to improve the "classname -> byte[]" step.

I used something like

JarEntry entry = (JarEntry) jarFile.getEntry( name+".class" );
InputStream stream = jarFile.getInputStream(entry);
int size = (int) entry.getSize();
byte[] code = new byte[size];

I also stated with URL but gave it up, because of unknown length.
If I really wanted to load classes remotelly, I'd download jars first 
then load classes from local copies.

Regards...

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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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