private void getDemoFile(final String fileName, final DemoCallback callback) {
FileMgr.requestFileSystem(LocalFileSystem.PERSISTENT, new FileSystemCallback() {
@Override
public void onSuccess(FileSystem fs) {
fs.getRoot().getDirectory("gwtmobile-phonegap", new FileOptions().create(true), new EntryCallback() {
@Override
public void onSuccess(Entry entry) {
DirectoryEntry dir = (DirectoryEntry) entry;
dir.getFile(fileName, new FileOptions().create(true), new EntryCallback() {
@Override
public void onSuccess(Entry entry) {
FileEntry file = (FileEntry) entry;
callback.onSuccess(file);
}