Torsten Curdt pisze:
Just a quick comment: static + classloader == evil ;-)
:-)
Yes, I thought the same but is there any other solution in scenario I outlined when it's thirdparty
class that creates a new instance of your class, which in turn needs to access some of your resources?
3. Then another class (3RDPARTY) is being loaded which is not part of
my block, it's from third-party jar. It's loaded by parent classloader
to ResourceStoreClassLoader. As part of configuration of this class I
pass a name of class which is some kind of extension point and is
implemented by class coming from my block; let's call this class
EXTENSION.
4. 3RDPARTY creates new instance of EXTENSION class (and this class is
again not loaded by ResourceStoreClassLoader but by parent), but in
EXTENSION class one tries to access field set in STATIC.
5. While EXTENSION tries to access STATIC, STATIC is being loaded
again, using parent classloader. The value in STATIC is gone, obviously.
So the basic problem is that, this STATIC class is loaded by two
different classloaders.
I'm wondering if there is any kind of general solution to such
problems. The only one I can think of is to enforce loading of
3RDPARTY class by ResourceStoreClassLoader so everything stays within
one classloader and even reflection tricks are not dangerous.
Well, if you think about it: with this setup there is no other way
around to have the parent classloader know of the static class to have
this problem resolved. As you can't (?) modify the parent classloader
your only chance is to have the EXTENSION loaded by the RSCL as well.
But how this can be enforced? I mean, 3RDPARTY is loaded by parent and 3RDPARTY, when tries to
create a new instance of EXTENSION uses it's own classloader thus uses parent. The only solution I
can see here is that I load 3RDPARTY using classloader coming from JCI so then EXTENSION will be
loaded with this classloader as well.
Am I missing something?
I would take a step back and re-think the situation. This static stuff
smells like wants to be replaced ;-)
If I knew how to do it, I would go with that direction immediately. :-P
Basically, the problem is that one wants to access Spring's application context within EXTENSION's
constructor. Any suggestion how to do it without using static class?
However, that would mean that one needs to modify commons-jci project.
Why? How?
I was thinking to enforce ResourceStoreClassLoader to load everything but I know that it's not the
best idea...
--
Grzegorz Kossakowski
