For every usage of Ant class api, different class loader

[Raja Nagendra Kumar]

Hi,

When we are using Ant.java/class api Is it possible to explicitly set the new class loader, even if the initial classes existed in system classloader( i.e though classpath or in ant lib directory.)

The issue we are seeing is when we load our custom tasks though taskdef, new classloader is being used for every programmatic ant call there fore static blocks are reinitialised for every sub ant project, however when  when we put it in lib or in system classpath, distinct classloader is not used..hence we have issue with some static code :) not being reinitialized.

Once we understand classloder  behaviors in ant based on project vs subproject and TaskDef classpath way and systemclasspath way, then we could be more confident to fix the current issue.

Looking for experts help.

Regards,
Raja Nagendra Kumar,
C.T.O
www.tejasoft.com

[Stefan Bodewig]

On 2009-11-05, Raja Nagendra Kumar <Nagendra.Raja@...> wrote:

> When we are using Ant.java/class api Is it possible to explicitly set the
> new class loader, even if the initial classes existed in system classloader(
> i.e though classpath or in ant lib directory.)
>
> The issue we are seeing is when we load our custom tasks though taskdef, new
> classloader is being used for every programmatic ant call there fore static
> blocks are reinitialised for every sub ant project, however when  when we
> put it in lib or in system classpath, distinct classloader is not
> used..hence we have issue with some static code :) not being reinitialized.

Don't use static blocks 8-)

Alternatively, don't make your jars available in the system classloader
or use the (deprecated) reverseloader attribute of taskdef.

> Once we understand classloder  behaviors in ant based on project vs
> subproject and TaskDef classpath way and systemclasspath way, then we could
> be more confident to fix the current issue.

It doesn't have any real relation to subprojects at all.  Ant normally
delegates loading of any classes up the classloader chain.

Stefan

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[Raja Nagendra Kumar]

Hi Stefan,

I was waiting for you replies.. all these days.. Thank you for answering this..

>Don't use static blocks 8-)

Sure we shall change this.

>Alternatively, don't make your jars available in the system classloader
This we have to put it in system class loader as we started using the Custom Executor  for the purpose of Virtual Targets handling.

If ant could consider such needs, and expose a property approach as in the feature request..
http://old.nabble.com/Feature-Request---Executor-setting-though-the-script-td26208582.html
we could avoid it. I would appricate your comments on this feature.

>or use the (deprecated) reverseloader attribute of taskdef.

ok, in this approach, could you pl. let me know how this attribute change the class loading.. and its impact with static blocks

> subproject and TaskDef classpath way and systemclasspath way, then we could

When we give a jar both in TaskDef classpath inner task and also in system classpath,
would the class be loaded from system or from taskdef classpath.

Regards,
Nagendra

[Stefan Bodewig]

On 2009-11-05, Raja Nagendra Kumar <Nagendra.Raja@...> wrote:

> I was waiting for you replies.. all these days.. Thank you for answering
> this..

Unless I'm mistaken there has been less than four hours between your
mail and my response ...

Please understand that I work on open source projects on my free time
like early mornings (when I reponded to your mail) or my lunchbreak
(right now) and that Ant is not the only project I work on.

>> or use the (deprecated) reverseloader attribute of taskdef.

> ok, in this approach, could you pl. let me know how this attribute change
> the class loading.. and its impact with static blocks

Usually when you have a nested classpath Ant will still consult the
system classloader before the classpath you've specified when trying to
load a class (this usually is what you want).  If you set reverseloader
to true it will look into the specified classpath before consulting the
system classloader.

Stefan

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[mgainty]

came up on maven users where a build engineer wanted to call a custom task which would load using his provided classloader
the only way I knew how to implement any ant task using supplied classloader was for the classloader to create a whole new project (build.xml)

(i suspect reverseloader would have at least provided the build engineer the custom classpath he desired)
unsure as to all the implications of using custom classloader over default system classloader
?
*gruss*
Martin Gainty
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> From: bodewig@...
> To: dev@...
> Subject: Re: For every usage of Ant class api, different class loader
> Date: Thu, 5 Nov 2009 14:29:41 +0100
>
> On 2009-11-05, Raja Nagendra Kumar <Nagendra.Raja@...> wrote:
>
> > I was waiting for you replies.. all these days.. Thank you for answering
> > this..
>
> Unless I'm mistaken there has been less than four hours between your
> mail and my response ...
>
> Please understand that I work on open source projects on my free time
> like early mornings (when I reponded to your mail) or my lunchbreak
> (right now) and that Ant is not the only project I work on.
>
> >> or use the (deprecated) reverseloader attribute of taskdef.
>
> > ok, in this approach, could you pl. let me know how this attribute change
> > the class loading.. and its impact with static blocks
>
> Usually when you have a nested classpath Ant will still consult the
> system classloader before the classpath you've specified when trying to
> load a class (this usually is what you want).  If you set reverseloader
> to true it will look into the specified classpath before consulting the
> system classloader.
>
> Stefan
>
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> To unsubscribe, e-mail: dev-unsubscribe@...
> For additional commands, e-mail: dev-help@...
>

     
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[Raja Nagendra Kumar]

> Unless I'm mistaken there has been less than four hours between your mail and my response ...

Stefan, I am very impressed by your level of knowledge and your passion to help others. I was really needing your help and hence was very glad to receive your reply. Pl. don't think other wise.

Having come out of enterprise like sun and we started this small company 5 years ago around java product refactoring and test automation services. I understand the value of your kind of services.

Are u working on Tortoise also.. if yes, how do you manage c++ and java world.

Regards,
Nagendra

[Gilles Scokart]

An other aproach is to specify a loader id when declaring the tasks in the
parent project (and make sure your inherit this id in the subclass).


Gilles Scokart


2009/11/5 Stefan Bodewig <bodewig@...>

> On 2009-11-05, Raja Nagendra Kumar <Nagendra.Raja@...> wrote:
>
> > When we are using Ant.java/class api Is it possible to explicitly set the
> > new class loader, even if the initial classes existed in system
> classloader(
> > i.e though classpath or in ant lib directory.)
> >
> > The issue we are seeing is when we load our custom tasks though taskdef,
> new
> > classloader is being used for every programmatic ant call there fore
> static
> > blocks are reinitialised for every sub ant project, however when  when we
> > put it in lib or in system classpath, distinct classloader is not
> > used..hence we have issue with some static code :) not being
> reinitialized.
>
> Don't use static blocks 8-)
>
> Alternatively, don't make your jars available in the system classloader
> or use the (deprecated) reverseloader attribute of taskdef.
>
> > Once we understand classloder  behaviors in ant based on project vs
> > subproject and TaskDef classpath way and systemclasspath way, then we
> could
> > be more confident to fix the current issue.
>
> It doesn't have any real relation to subprojects at all.  Ant normally
> delegates loading of any classes up the classloader chain.
>
> Stefan
>
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> To unsubscribe, e-mail: dev-unsubscribe@...
> For additional commands, e-mail: dev-help@...
>
>

[Stefan Bodewig]

On 2009-11-07, Gilles Scokart <gscokart@...> wrote:

> An other aproach is to specify a loader id when declaring the tasks in the
> parent project (and make sure your inherit this id in the subclass).

IIRC Raja's problem was that static blocks didn't get re-run for
projects if the tasks where sharing the same classloader (because the
system classloader was used)

> On 2009-11-05, Raja Nagendra Kumar <Nagendra.Raja@...> wrote:

>> The issue we are seeing is when we load our custom tasks though
>> taskdef, new classloader is being used for every programmatic ant
>> call there fore static blocks are reinitialised for every sub ant
>> project, however when when we put it in lib or in system classpath,
>> distinct classloader is not used..hence we have issue with some
>> static code :) not being reinitialized.

loaderref would make things consistent, but different from what Raja
actually wants.

Stefan

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