TC 6/7 class loaders

[Rainer Jung <ra...@kippdata.de>]

In theory we still support splitted server / common /shared class
loaders. But providing classes via the server loader does not work out
of the box. E.g. I remember some TC 6 situation in 2009 where someone
wanted to provide a special listener and put it into the server loader
and *not* into the common loader. But that lead to a CNFE, because
"org.apache.catalina.core.StandardServer" was loaded by the common
loader. To fix it, he had to reorder the Jars in the old TC 5.5 layout
including splitting up Jars combined for TC 6 into one file into
separate Jars for server and common.

Does anyone actually use the server loader? By default server and shared
loaders delegate everything to the common loader, because their search
path is empty. If there is no known use case for the server loader we
might as well remove it at least for TC 8.

Should we document how to use the server loader (minimum Jar
rearrangement) or is this unwanted, because server is kind of deprecated?

I guess we should still keep shared, because although it is generally
not recommended I can at least imagine how to use it. But for "server" I
have some doubts.

Regards,

Rainer




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Re: TC 6/7 class loaders

[Konstantin Kolinko <kn...@gmail.com>]

2011/7/29 Rainer Jung <ra...@kippdata.de>:
> In theory we still support splitted server / common /shared class
> loaders. But providing classes via the server loader does not work out
> of the box. E.g. I remember some TC 6 situation in 2009 where someone
> wanted to provide a special listener and put it into the server loader
> and *not* into the common loader. But that lead to a CNFE, because
> "org.apache.catalina.core.StandardServer" was loaded by the common
> loader. To fix it, he had to reorder the Jars in the old TC 5.5 layout
> including splitting up Jars combined for TC 6 into one file into
> separate Jars for server and common.
>
> Does anyone actually use the server loader? By default server and shared
> loaders delegate everything to the common loader, because their search
> path is empty. If there is no known use case for the server loader we
> might as well remove it at least for TC 8.
>
> Should we document how to use the server loader (minimum Jar
> rearrangement) or is this unwanted, because server is kind of deprecated?
>
> I guess we should still keep shared, because although it is generally
> not recommended I can at least imagine how to use it. But for "server" I
> have some doubts.
>

I think that it is possible to document Server classloader, but one
should clearly state that it is deprecated for a reason:

One should read and understand ClassLoader HOWTO and be able to deal
with dependencies mess.  Having to move some jars around is a
reasonable price for that. (I do not want to list what jars those
are).

BTW,
1) IIRC, using privileged="true" in Context will make it to use the
server classloader
2) One has to update catalina.policy if that is used.


I think I'll update class-loader-howto.html soon, because I see some
typos/ glitches there.

Best regards,
Konstantin Kolinko

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