Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
Flume >> mail # dev >> Why does ComponentConfigurationFactory.create pass classname as part of init


Copy link to this message
-
Re: Why does ComponentConfigurationFactory.create pass classname as part of init
I don't remember why I did this at that time. I will take a look at this when I get some time and get back to you. FWIW, this is part of a yet to be completed component-wise configuration system which I plan to get back to some time soon. Hopefully, this is not a blocker for you as of now.  

Thanks,
Hari

--
Hari Shreedharan
On Wednesday, September 19, 2012 at 11:02 PM, David Capwell wrote:

> I guess my real question would be why my custom ComponentConfiguration has to have this constructor.  Here is quick sample of what i mean:
>
> public void createInstance() {
>     final ComponentConfiguration config = ComponentConfigurationFactory.create(
>         "name",
>         RandomConfig.class.getName(),
>         ComponentConfiguration.ComponentType.SOURCE);
>   }
>
>   public static class RandomConfig extends ComponentConfiguration {
>
>     public RandomConfig() {
>       super("my awesome name");
>     }
>   }
>
>
> This fails since the constructor doesn't exist.  If i add a param "String ignored" then it works just fine.
> On Wed, Sep 19, 2012 at 10:47 PM, Hari Shreedharan <[EMAIL PROTECTED] (mailto:[EMAIL PROTECTED])> wrote:
> > From: http://docs.oracle.com/javase/tutorial/reflect/member/ctorInstance.html
> > There are two reflective methods for creating instances of classes: java.lang.reflect.Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) and Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29). The former is preferred and is thus used in these examples because:
> > Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) can only invoke the zero-argument constructor, while Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) may invoke any constructor, regardless of the number of parameters.
> > Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) throws any exception thrown by the constructor, regardless of whether it is checked or unchecked. InvocationTargetException (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/InvocationTargetException.html).
> > Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) requires that the constructor be visible; Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) may invoke private constructors under certain circumstances.
> >
> >
> >
> >
> > Thanks,
> > Hari
> >
> > --
> > Hari Shreedharan
> >
> >
> > On Wednesday, September 19, 2012 at 10:20 PM, David Capwell wrote:
> >
> > > I was going over the flume 1.2.0 code and i was wondering why
> > > the ComponentConfigurationFactory.create class has the following:
> > >
> > > confType = (Class<? extends ComponentConfiguration>) Class.forName(type);
> > > return confType.getConstructor(String.class).newInstance(type);
> > >
> > > Since type is the class, then why does the the class need a constructor
> > > that puts in the class name?
> > >
> > > thanks for your time reading this email.
> >
>