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Groups > comp.lang.java.programmer > #28350

Re: limitations of Class.forName

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On 02.05.2014 02:42, Roedy Green wrote:
> When I first encountered Java, I was very excited about the notion
> of interfaces and dynamic loading. I thought it would let people plug
> in their own code to every conceivable utility.
>
> There are two catches.
>
> 1. arranging that java.exe will look for your dynamic class in the
> place where it is.  It will not usually be bundled in the original
> jar.

It's not only java.exe, but also java (on other platforms), java plugin etc.

> 2. arranging that java.exe will look for any auxiliary classes your
> plugin needs in the place where they live.
>
> A garden variety jar prevents java from looking anywhere else for
> classes.

You can have a classpath header in the JAR manifest.  You can use that 
to do relative references, i.e. via same directory or URL that hosts the 
referencing JAR.

> I thought I would write a short essay on this.  What techniques are
> available?

See Arne's reply.  Usually you configure the URL (or a directory name or 
...) and create a classloader or classloaders that will look there.

> I have always skirted the problem by putting all classes in the
> original jar.

I don't think that's a good idea because it makes composing of an 
application harder than necessary.

Also, various container systems have solved this already - you just need 
to look how JEE containers and Tomcat are doing things.

Cheers

	robert

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Thread

limitations of Class.forName Roedy Green <see_website@mindprod.com.invalid> - 2014-05-01 17:42 -0700
  Re: limitations of Class.forName Arne Vajhøj <arne@vajhoej.dk> - 2014-05-01 21:15 -0400
  Re: limitations of Class.forName Robert Klemme <shortcutter@googlemail.com> - 2014-05-02 08:51 +0200
  Re: limitations of Class.forName Josip Almasi <joe@vrspace.org> - 2014-05-02 09:25 +0200
    Re: limitations of Class.forName Roedy Green <see_website@mindprod.com.invalid> - 2014-05-06 03:55 -0700

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