Handle unclosed after reading jar content

Question

Hi
While attempting to build a simple dynamic plugin (or 'service', as in sun terminology) framework for my app,
I encountered a behavior which seems at least unwanted to me:
After opening a stream using a java.net.URL to a file inside a jar file, closing it wont close the handle on the jar file.
To make it easy, here is a simple piece of code that causes the problem:
public static void main(String[] args) throws IOException {
          InputStream inputstream = null;
          BufferedReader bufferedreader = null;
          try {
               // URL to a local jar file
               // the jar and service file do exist
               URL url = new URL("jar", "", "file:/d:/temp/jars/ri.jar!/META-INF/services/test.plugin.Plugin");
               inputstream = url.openStream();
               bufferedreader = new BufferedReader(new InputStreamReader(inputstream, "utf-8"));
               // do some stuff
          } finally {
               if (inputstream != null) {
                    inputstream.close();
               if (bufferedreader != null) {
                    bufferedreader.close();
          // force garbage just in case
          inputstream = null;
          bufferedreader = null;
          System.gc();
          System.gc();
          // pause before exit
          // at this point, there is still a handle on the jar file from the JVM
          System.out.print("pause;");
          Scanner in = new Scanner(System.in);
          in.nextLine();
     }When reaching the 'pause' step, a handle exists on the file and makes any action on it impossible
(replacing it with a new one for instance). To confirm this, Process Explorer detects a handle from
the javaw process associated with this program on the jar file.
I've experienced this using the latest of jdk 6 and also with java 5 (on win XP)
So, is this a normal behavior ? Any idea how to avoid it ?
As I'm looking for dynamic plugin functionnalities, I'd like to keep this jar content as it is,
ie this file which lists implementations of the "test.plugin.Plugin" service among the classes
which are also stored in the jar.
Being able to release the jar file would mean I can replace it with another version on fly,
without restarting my app, and load it again to access the updated functionnalities, then
unload it again and so on.
Thanks in advance for any piece of advice on this issue.

Answer 1

in case anyone is interested, I seemed to have found a workaround, by disabling caching for the URL connection:
if we replace
inputstream = url.openStream();
bufferedreader = new BufferedReader(new InputStreamReader(inputstream, "utf-8"));
// do some stuffwith
final URLConnection connection = url.openConnection();
inputstream = connection.getInputStream();
bufferedreader = new BufferedReader(new InputStreamReader(inputstream, "utf-8"));
// do some stuff
connection.setDefaultUseCaches(false);the handle on the jar file is not kept after closing stream.