在Android 11中，应用程序默认无法读写SD卡/Android/someapp目录。若需要访问该目录，需要利用媒体存储库(MediaStore)来进行文件I/O操作。以下是一个简单的代码示例：

private static final String RELATIVE_DIRECTORY = "/someapp/"; // 相对目录名
private static final String MIME_TYPE_TEXT = "text/plain"; // 文件类型

// 获取sdcard/Android/someapp目录
public static File getExternalStorageDirectory(Context context) {
    File file;
    if (context.getExternalMediaDirs().length > 0) {
        // 检查应用程序目录是否存在
        file = new File(context.getExternalMediaDirs()[0], RELATIVE_DIRECTORY);
        if (!file.exists()) {
            if (!file.mkdirs()) {
                Log.e(TAG, "getExternalStorageDirectory: failed to create directory");
                return null;
            }
        }
    } else {
        Log.e(TAG, "getExternalStorageDirectory: external media dirs length <= 0");
        file = context.getExternalFilesDir(null);
    }
    return file;
}

// 写入文件内容到sdcard/Android/someapp目录
public static boolean writeFileToExternalStorage(Context context, String fileName, String content){
    File file = new File(getExternalStorageDirectory(context), fileName);
    try {
        FileWriter writer = new FileWriter(file, false);
        writer.write(content);
        writer.flush();
        writer.close();
        return true;
    } catch (IOException e) {
        Log.e(TAG, "writeFileToExternalStorage: failed to write file", e);
        return false;
    }
}

// 读取文件内容从sdcard/Android/someapp目录
public static String readFileFromExternalStorage(Context context, String fileName){
    File file = new File(getExternalStorageDirectory(context), fileName);
    try {
        BufferedReader reader = new BufferedReader(new FileReader(file));
        StringBuilder content = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            content.append(line).append("\n");
        }
        reader.close();
        return content.toString