Use versioned extension cache entry, if we have...

a version. Otherwise the extension JNLP will be downloaded a 2nd time and
a second entry will be created:
::i=0\13::l=http://localhost/myapp/jnlp.extension/common.jnlp::a=1706698483984::
::i=0\0::l=http://localhost/myapp/jnlp.extension/common.jnlp::v=6.2.3::a=1706698483198::

Because the cache lookup is called twice on extensions. The second time without the version
so the versioned entry is not used. Instead a new entry i=0\13 without a version is created.

This works fine as long as not a new version of common.jnlp::v=6.2.4 is lookuped.
Then the sorting in line 246 of net/adoptopenjdk/icedteaweb/resources/cache/CacheImpl.java
fails withe a NPE, because it's missing the version.

Author: tzjan

core/src/main/java/net/adoptopenjdk/icedteaweb/jnlp/element/resource/ExtensionDesc.java

@@ -131,7 +131,7 @@ public URL getLocation() {
      */
     public void resolve() throws ParseException, IOException {
         if (file == null) {
-            file = new JNLPFileFactory().create(location);
+            file = new JNLPFileFactory().create(location, version);
 
             LOG.debug("Resolve: {}", file.getInformation().getTitle());
 

core/src/main/java/net/sourceforge/jnlp/JNLPFileFactory.java

@@ -49,6 +49,31 @@ public JNLPFile create(final URL location) throws IOException, ParseException {
         return create(location, new ParserSettings());
     }
 
+    /**
+     * Generate unique key from file URL
+     * @param location
+     */
+    private String createUniqueKey(final URL location) {
+        return Calendar.getInstance().getTimeInMillis() + "-" + ((int) (Math.random() * Integer.MAX_VALUE)) + "-" + location;
+    }
+
+    /**
+     * Create a JNLPFile from a URL and parent URLm a version and checking for
+     * updates using the specified policy.
+     *
+     * @param location the location of the JNLP file
+     * @param version  the version of the JNLP file
+     * @throws IOException    if an IO exception occurred
+     * @throws ParseException if the JNLP file was invalid
+     */
+    public JNLPFile create(final URL location, final VersionString version) throws IOException, ParseException {
+        return create(location,
+                      createUniqueKey(location),
+                      version,
+                      new ParserSettings(),
+                      JNLPRuntime.getDefaultUpdatePolicy());
+    }
+
     /**
      * Create a JNLPFile from a URL checking for updates using the
      * default policy.
@@ -59,7 +84,7 @@ public JNLPFile create(final URL location) throws IOException, ParseException {
      * @throws ParseException if the JNLP file was invalid
      */
     public JNLPFile create(final URL location, final ParserSettings settings) throws IOException, ParseException {
-        final String uniqueKey = Calendar.getInstance().getTimeInMillis() + "-" + ((int) (Math.random() * Integer.MAX_VALUE)) + "-" + location;
+        final String uniqueKey = createUniqueKey(location);
         return create(location, uniqueKey, null, settings, JNLPRuntime.getDefaultUpdatePolicy());
     }