Allow AWT Desktop class to launch urls and files

by replacing gnome_url_show() call (it may also
call gtk_show_uri()) by a 'xdg-open' command,
which will work inside the flatpak sandbox, and
for any desktop environment not just GTK/Gnome.

Many Java apps in flathub are SWT apps which are
built upon the minimal Freedesktop runtime, and
they are currently broken with respect to launch
web links or open local files, this commit patches
the Desktop class so it can work under the sandbox.

flathub#15

java_desktop_xdg_open.patch

@@ -0,0 +1,50 @@
+--- a/src/java.desktop/unix/classes/sun/awt/X11/XDesktopPeer.java	2021-01-16 18:10:28.246735459 -0400
++++ b/src/java.desktop/unix/classes/sun/awt/X11/XDesktopPeer.java	2021-01-16 22:12:54.371818460 -0400
+@@ -59,8 +59,7 @@
+         XToolkit.awtLock();
+         try {
+             if (!initExecuted) {
+-                nativeLibraryLoaded = init(UNIXToolkit.getEnabledGtkVersion()
+-                        .getNumber(), UNIXToolkit.isGtkVerbose());
++                nativeLibraryLoaded = false;
+             }
+         } finally {
+             initExecuted = true;
+@@ -75,7 +74,7 @@
+
+     static boolean isDesktopSupported() {
+         initWithLock();
+-        return nativeLibraryLoaded && !supportedActions.isEmpty();
++        return /*nativeLibraryLoaded &&*/ !supportedActions.isEmpty();
+     }
+
+     public boolean isSupported(Action type) {
+@@ -109,22 +108,19 @@
+     }
+
+     private void launch(URI uri) throws IOException {
+-        byte[] uriByteArray = ( uri.toString() + '\0' ).getBytes();
+         boolean result = false;
++        int ret = -1;
+         XToolkit.awtLock();
+         try {
+-            if (!nativeLibraryLoaded) {
+-                throw new IOException("Failed to load native libraries.");
+-            }
+-            result = gnome_url_show(uriByteArray);
++            ret = Runtime.getRuntime().exec(new String[] {"xdg-open", uri.toString()}).waitFor();
++            result = ret == 0;
++        } catch (InterruptedException e) {
++            System.err.println("Caught InterruptedException: " + e.getMessage());
+         } finally {
+             XToolkit.awtUnlock();
+         }
+         if (!result) {
+-            throw new IOException("Failed to show URI:" + uri);
++            throw new IOException("xdg-open failed with error code "+ ret +" for URI: " + uri);
+         }
+     }
+-
+-    private native boolean gnome_url_show(byte[] url);
+-    private static native boolean init(int gtkVersion, boolean verbose);
+ }

org.freedesktop.Sdk.Extension.openjdk11.yaml

@@ -96,6 +96,9 @@ modules:
         path: 39020dd9b75f
       - type: patch
         path: 371bbe373ae0
+      - type: patch
+        # https://github.com/flathub/org.freedesktop.Sdk.Extension.openjdk11/issues/15
+        path: java_desktop_xdg_open.patch
   - name: cacerts
     buildsystem: simple
     sources: