Re: ClassLoaders and finding fully-qualified names

From:

"Karl Uppiano" <karl.uppiano@verizon.net>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 29 Dec 2006 21:43:55 GMT

Message-ID:

<v_flh.438$oW4.321@trndny05>

"ballpointpenthief" <ballpointpenthief@yahoo.co.uk> wrote in message
news:1167370241.683296.259240@i12g2000cwa.googlegroups.com...

I haven't managed to find and information on this so far...

There exists a file for 'mypackage.Hello' that a user wants to load as
a Class in an application.

A user selects the Hello.class file from a JFileChooser.
The Hello.class file is sent to subclass of SecureClassLoader.
The ClassLoader needs the fully-qualified classname (mypackage.Hello)
to define the class (along with the bytecode, and the CodeSource),
so....

how can I find out that Hello is in 'mypackage' if all I have is the
File?

Thanks!
Matt

Class loader behavior depends on the class loader implementation. You can
write a class loader to do whatever you want, within the constraints of the
class loader design patterns. Packages are typically anchored to the
directory hierarchy relative to the classpath directory. This is true for
classes lying "loose" in the file system, and for classes in a jar file.
Without the directory structure, you might have a problem.

It might be helpful to look here
(http://java.sun.com/j2se/1.5.0/docs/api/java/lang/ClassLoader.html) and
here (http://java.sun.com/j2se/1.5.0/docs/api/java/net/URLClassLoader.html)
to really understand class loaders. If you cannot find a class loader that
does what you need, you might be able to write one. People often confuse the
behavior of the default class loader with class loaders in general, or with
the Java spec itself.