Re: changing the classpath at runtime in code

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 26 Oct 2007 22:50:46 -0400

Message-ID:

<4722a775$0$90266$14726298@news.sunsite.dk>

Aryeh M. Friedman wrote:

On Oct 24, 9:31 pm, Arne VajhHj <a...@vajhoej.dk> wrote:

Aryeh M. Friedman wrote:

On Oct 24, 9:13 pm, Arne VajhHj <a...@vajhoej.dk> wrote:

Aryeh M. Friedman wrote:

On Oct 24, 8:16 pm, Arne VajhHj <a...@vajhoej.dk> wrote:

Aryeh M. Friedman wrote:

Is it possible for a java app to change it's classpath at runtime. I
tried:
System.setProperty("java.class.path","foo")
The reason for wanting to try is URLClassLoader will not physically
reread a class file if it is in the classpath.

Create a URLClassLoader with a url that are *not* in the parent
classloaders url's.

so just do:
URL[] url={new URL("file://foo")};
URLClassLoader laoder=new URLClassLoader(url);
?

I have a little demo example I often use to illustrate
(subdir test is not in classpath of program).

You posted this in the original thread but as noted in the linked to
thread almost all the classes I am dealing with *WILL* be in the
classpath.... so the question remains if I do the code in my previous
post will it now load from the class path or from "foo".

If the class get loaded by the parent classloader because it is
in the apps general classpath, then you can (as far as I know)
neither get it unloaded or reloaded.

You need to get those classes of the classpath.

Since this is for a commercial unit testing product this is not
possible in practice (it is not safe to make assumptions about where
people place things). Some one off line suggested forking a process
to do it.... if I can't find a ClassLoader based solution I will have
to do that but it is down right a) not portable b) evil

You do not have any control over where people put their stuff,
but you have control over your stuff.

If the only thing in classpath is your jar file, then you can
create your own classloader for their stuff and unload and reload
as needed.

Arne