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Date: Thu, 20 Mar 2014 11:19:19 +0200
Message-ID: 
 <CAAMYKhowDoC9JSTowhCyzQBw4=zsE5947nfMqKCQ1dCpv4NEDQ@mail.gmail.com>
Subject: Re: Class loading in Hadoop and HBase
From: Amit Sela <amits@infolinks.com>
To: user@hbase.apache.org
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And what's wrong with: ClassLoader cl = Clazz.class.getClassLoader();


On Thu, Mar 20, 2014 at 11:03 AM, haosdent <haosdent@gmail.com> wrote:

> > should prefer the Class's CL because the client's application affects the
> TCCL.
> You could call "Thread.currentThread().setContextClassLoader(classLoader)"
> before the classloader load "Configuration" or "HbaseObjectWritable" class.
>
> You consider the logic below should be better:
> ClassLoader cl = Clazz.class.getClassLoader();
> if (cl == null) {
>    cl = Thread.currentThread().getContextClassLoader();
> }
>
> But variable "cl" couln't be null here. So the code snippet above is
> equivalent to the following code:
>
> ClassLoader cl = Clazz.class.getClassLoader();
>
>
> On Thu, Mar 20, 2014 at 4:39 PM, Amit Sela <amits@infolinks.com> wrote:
>
> > I understand the benefits of TCCL, but I think, and I would like to hear
> > the "why not", that code that may run in the client side (like in the
> case
> > of Configuration and HbaseObjectWritable examples I gave) should prefer
> the
> > Class's CL because the client's application affects the TCCL.
> >
> >
> > On Thu, Mar 20, 2014 at 8:56 AM, haosdent <haosdent@gmail.com> wrote:
> >
> > > Because we could change the value of "Thread.currentThread().
> > > getContextClassLoader()" by
> > "Thread.currentThread().setContextClassLoader(
> > > classLoader)". But we couldn't change the value of
> > > "this.getClass().getClassLoader()".
> > > Maybe a little confused, TCCL is more flexible than the class's CL.
> > >
> > >
> > > On Thu, Mar 20, 2014 at 2:43 PM, Amit Sela <amits@infolinks.com>
> wrote:
> > >
> > > > I understand that. But why ? Why prefer the TCCL over the class's CL
> ?
> > > > On Mar 20, 2014 3:00 AM, "haosdent" <haosdent@gmail.com> wrote:
> > > >
> > > > > Sometimes we would use
> "Thread.currentThread().setContextClassLoader(
> > > > > classLoader);" to specify classloader. So
> > > > > "Thread.currentThread().getContextClassLoader();"
> > > > > should be the first choice.
> > > > >
> > > > >
> > > > > On Thu, Mar 20, 2014 at 1:53 AM, Amit Sela <amits@infolinks.com>
> > > wrote:
> > > > >
> > > > > > Hi all,
> > > > > > I'm running with Hadoop 1.0.4 and HBase 0.94.12 bundled (OSGi)
> > > > versions I
> > > > > > built.
> > > > > > Most issues I encountered are related to class loaders.
> > > > > >
> > > > > > One of the patterns I noticed in both projects is:
> > > > > >
> > > > > >     ClassLoader cl =
> > Thread.currentThread().getContextClassLoader();
> > > > > >       if(cl == null) {
> > > > > >       cl = Clazz.class.getClassLoader();
> > > > > >     }
> > > > > >
> > > > > > Where Clazz is the Class containing this code.
> > > > > >
> > > > > > I was wondering about this choice... Why not go the other way
> > around:
> > > > > >
> > > > > >     ClassLoader cl = Clazz.class.getClassLoader();
> > > > > >       if(cl == null) {
> > > > > >       cl = Thread.currentThread().getContextClassLoader();
> > > > > >     }
> > > > > >
> > > > > > And in a more general note, why not always use Configuration (and
> > let
> > > > > it's
> > > > > > cl be this.getClass().getClassLoader()) to load classes ?
> > > > > >
> > > > > > That would surely help in integration with modularity frameworks.
> > > > > >
> > > > > > Thanks,
> > > > > > Amit.
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Best Regards,
> > > > > Haosdent Huang
> > > > >
> > > >
> > >
> > >
> > >
> > > --
> > > Best Regards,
> > > Haosdent Huang
> > >
> >
>
>
>
> --
> Best Regards,
> Haosdent Huang
>

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