Android圖片操作-保存圖片到SD卡

/**
     * Save Bitmap to a file.保存圖片到SD卡。
     * 
     * @param bitmap
     * @param file
     * @return error message if the saving is failed. null if the saving is
     *         successful.
     * @throws IOException
     */
    public static void saveBitmapToFile(Bitmap bitmap, String _file)
            throws IOException {
        BufferedOutputStream os = null;
        try {
            File file = new File(_file);
            // String _filePath_file.replace(File.separatorChar +
            // file.getName(), "");
            int end = _file.lastIndexOf(File.separator);
            String _filePath = _file.substring(0, end);
            File filePath = new File(_filePath);
            if (!filePath.exists()) {
                filePath.mkdirs();
            }
            file.createNewFile();
            os = new BufferedOutputStream(new FileOutputStream(file));
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, os);
        } finally {
            if (os != null) {
                try {
                    os.close();
                } catch (IOException e) {
                    Log.e(TAG_ERROR, e.getMessage(), e);
                }
            }
        }
    }