Re: What does this snippet do?

Owen Jacobson <>
Mon, 3 Dec 2007 21:30:54 -0800 (PST)
On Dec 3, 9:15 pm, Ramon F Herrera <> wrote:

This question would be best answered by somebody with a knowledge of
component based programming methodologies, such as COM, CORBA or the
UNO newcomer; as implemented in Java, of course.

This comes from one of the tutorial examples contained in the
OpenOffice SDK.

I discovered that if I remove the code below, the sample program still
works properly, while being run from inside Eclise or NetBeans. I
removed the code and forgot all about it.

Some time later, I realized that the program didn't run standalone,
from the Unix or Windows shell/CLI, or by double click. So, I put the
chunk of code back, and voila! the program works fine now.

I could try reading the OO developer manual and following the code,
but I am sure some expert out there can give a better explanation.

This whole component based approach looks very intriguing, but somehow
counterintuitive, at least to me.

Thanks for sharing your insight...



 ClassLoader loader = ClassLoader.getSystemClassLoader();
 if (loader instanceof URLClassLoader) {
     URLClassLoader cl = (URLClassLoader)loader;
     Class sysclass = URLClassLoader.class;
      try {
           Method method = sysclass.getDeclaredMethod("addURL", new
           method.invoke(cl, new Object[]{new
           } catch (Throwable t) {
                    throw new IOException("Error, could not add URL to
system classloader");
 } else {
          System.out.println("Error occured, URLClassLoader expected
but " +
          loader.getClass() + " received. Could not continue.");

It adds an extra path to the system classloader's search path in a
particularly heinous way: it reaches into an internal method,
bypassing the "protected" access modifier on URLClassLoader.addURL via

I shudder to read such code. Eegh. It betrays a weak understanding
of Java's classloading model; the desired effect would be better
achieved by creating a new URLClassLoader as a child of the system
classloader with the OO path in the new loader's search path.
However, other parts of the application might need to be adjusted to
be "aware" of the custom classloader.

More simply, you should add the OpenOffice java path to the Class-Path
or -classpath as appropriate. Unfortunately, since the OpenOffice
java path is highly system-dependent that's hard to do.

See the documentation of ClassLoader:
and URLClassLoader:
for details.


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