private String readFile(File f) throws FileNotFoundException, IOException {
        FileReader fr = new FileReader(f);
        BufferedReader br = new BufferedReader(fr);
        StringBuilder b = new StringBuilder();
        String zeile;
        do {
            zeile = br.readLine();
            b.append(zeile);
        } while (zeile != null);
        br.close();
        return b.toString();
    }