private void removeFromUriCache(final Uri uri) {
        final String docUriToString = uri.toString();
        synchronized (this.folderUriCache) {
            final Iterator<Map.Entry<String, Uri>> it = this.folderUriCache.entrySet().iterator();
            while (it.hasNext()) {
                if (it.next().getValue().toString().startsWith(docUriToString)) {
                    it.remove();
                }
            }
        }
    }
Gets the Folder File; creates it if necessary and performs all possible error handlings.
This is used for locations of Type DOCUMENT and FILE
<br
This method is in many respects the core method of this class

@param folder folder to get file for
@return file folder, or null if creation/retrieving was not at all possible
main/src/main/java/cgeo/geocaching/storage/DocumentContentAccessor.java