public static String readFile(String filePath) throws FileNotExistException {
        File file = new File(filePath);
        StringBuilder builder = new StringBuilder();
        if (!file.exists()) {
            throw new FileNotExistException(filePath);
        }
        try {
            BufferedReader buffer = new BufferedReader(new FileReader(file));
            String tmp = buffer.readLine();
            while (tmp != null) {
                builder.append(tmp);
                tmp = buffer.readLine();
                if (tmp != null)
                    builder.append('\n');
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return builder.toString();
    }