Code sharing between applets

Question

Hi,
I'm currently using Eclipse and JCOP plugin for applet development, and I'm looking for solutions on how to share custom libraries between applets. I'm particularly not looking for interface sharing between applets, but more how to organize the source code so I can include common custom classes in different applets (e.g. generic ASN1 parsing library, signature library etc)
Thank you for any feedback.

Answer 1

Thanks for the pointer! I also found this thread:
https://forums.oracle.com/thread/2217928?start=0&tstart=0
which cover the same topic with code examples to be very useful.
But I have stumbled upon a couple of problem wrt this approach which I can't quite isolate:
1. I've got a shell script which basically "tags" a package before build with the SVN version number, and if there are local modifications. This code is auto-generated in a file called svnversion.java inside commonlib package:
package commonlib;
public class svnversion {
  public static final byte[] TAG = {(byte) 0x00 ,(byte) 0xFB ,(byte) 0x3F } ;
  public static final boolean MODIFIED = true ;
When this code was in the same package as the applet, I had no problem accessing the TAG byte array, but after separating the applet and the commonlib in two separate packages, I get SW 0x6f00 whenever I touch the TAG byte array from my applet. I can access the MODIFIED variable, but not the TAG byte array.
(EDIT: Since commonlib declare TAG as a static final byte array, and final cannot be set to null upon release, maybe this is the cause for my memory leaks?)
2. I try to keep everything in commonlib static, and I've added an install() and release() hook in commonlib which keeps track of reference counter and acquire and release memory. Upon release I set every static variable to null. And I call commonlib.install() from the applet, and use AppletEvent and do commonlib.release() upon uninstall. But still it seems I fail to clean-up properly, because I end up in situations where I'm unable to delete the card content - presumably because a memory leak. So I have a few questions related to that:
a) How do I debug memory leaks?
b) In commonlib, if I do:
public class Common {
     private static DESKey des1Key = null;
     private static short refCount = 0;
     public static void install() {
          refCount++;
          if (des1Key == null)
               des1Key = (DESKey) KeyBuilder.buildKey(KeyBuilder.TYPE_DES, KeyBuilder.LENGTH_DES, false);
public static void release() {
     --refCount;
     if (refCount == 0)
          des1Key = null;
Is it a correct assumption that I need to set des1Key to null, because it is declared as static?
c) Does the following code snippets allocate memory, which needs to be freed?
md = MessageDigest.getInstance(MessageDigest.ALG_SHA_256, false);
and
rsaCipher = Cipher.getInstance(Cipher.ALG_RSA_NOPAD, false);
d) Say commonlib should hold one RSA key, but at install time we do not know the key size (actual size shall be requested by client). I chose this approach:
public class RSAlib {
     public static KeyPair rsaKeyPair = null;
     public static Cipher rsaCipher = null;
private static short refCount = 0;
     public static void install() {
refCount++;
          if (rsaCipher == null) {
              rsaCipher = Cipher.getInstance(Cipher.ALG_RSA_NOPAD, false);  }
     public static void release() {
          --refCount;
          if (refCount==0) {
               rsaCipher = null;
               rsaKeyPair = null;
public static void createRSAKeyPair(short keySize) {
     switch(keySize) {
     case (KeyBuilder.LENGTH_RSA_1024):
     case (KeyBuilder.LENGTH_RSA_2048):
          break;
     default:
          ISOException.throwIt(SW.CRYPTOGRAPHIC_ERROR);
     try {
          JCSystem.beginTransaction();
          rsaKeyPair = new KeyPair(KeyPair.ALG_RSA_CRT, keySize);
          JCSystem.requestObjectDeletion();
          JCSystem.commitTransaction();
     } catch (Exception e) {
          JCSystem.abortTransaction();
Is this correct usage of garbage collection (I know my JCOP card support it), and will this work in context of a commonlib?