Fix for issue jMonkeyEngine#2302 - NativeLibraryLoader fails due to no write permissions (jMonkeyEngine#2303)

* Fix for issue jMonkeyEngine#2302 - NativeLibraryLoader fails due to no write permissions
Extract native library to a folder directly beneath the user temp folder. Do not use an intermediate /jme subfolder.
Check the result of the call to mkdir. Use UserCache if creation failed.
Check if the extraction folder is actually writable. If not use the UserCache.
Updated log message: since a previous change we no longer extract to the working directory.

* Switch to a smaller change. Simply check if jmeTempDir is writable. If not, use user cache folder instead.

---------

Co-authored-by: andreas <awmross@test.com>
Co-authored-by: andreas <amross@fastmail.com>

Author: 3 people

jme3-desktop/src/main/java/com/jme3/system/NativeLibraryLoader.java

@@ -202,10 +202,14 @@ public static File getExtractionFolder() {
                     if (!jmeTempDir.exists()) {
                         jmeTempDir.mkdir();
                     }
-                    extractionFolder = new File(jmeTempDir, "natives_" + Integer.toHexString(computeNativesHash()));
-
-                    if (!extractionFolder.exists()) {
-                        extractionFolder.mkdir();
+                    if(!jmeTempDir.canWrite()) {
+                        setExtractionFolderToUserCache();
+                    } else {
+                        extractionFolder = new File(jmeTempDir, "natives_" + Integer.toHexString(computeNativesHash()));
+
+                        if (!extractionFolder.exists()) {
+                            extractionFolder.mkdir();
+                        }
                     }
                 } catch (Exception e) {
                     setExtractionFolderToUserCache();
@@ -268,7 +272,7 @@ private static void setExtractionFolderToUserCache() {
             extractionFolder.mkdir();
         }
 
-        logger.log(Level.WARNING, "Working directory is not writable. "
+        logger.log(Level.WARNING, "Temp directory is not writable. "
                                 + "Natives will be extracted to:\n{0}", 
                                 extractionFolder);
     }