最近有个需求，要获取设备唯一id，Android一直没有什么完善的方案获取设备唯一不变的id，我就结合了几种方案组成了一下：

1. 首先获取IMEI; IMEI获取失败后

2. 获取SN序列号，序列号失败后

3. 随机生成一串UUID存储在内存中

经过测试，在小米手机上存储会提示open failed: EACCES (Permission denied) 查了很多资料，常用的方案都做过尝试，例如：添加android:requestLegacyExternalStorage=”true”到清单中等方案都没有解决问题，下面说说我的解决方案：

给予所有文件读写权限，直接上代码

1. 清单文件中加入

<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"/>

这一步特别重要，不给这个权限，跳转后的按钮灰色无法点击

2.  只贴所有文件读写权限代码，基本读写权限还是需要动态申请的

private static final int REQUEST_CODE = 1024;

//Android 11需要申请所有文件读写权限
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
        //是否有所有问读写权限 
    if (Environment.isExternalStorageManager()) {
        //有所有文件读写权限  TODO something
    }else {
        //跳转到打开权限页面 
        Intent intent = new Intent(Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION);

        intent.setData(Uri.parse("package:" + mContext.getPackageName()));

        startActivityForResult(intent, REQUEST_CODE);


    }

}else {
   //TODO something
}

3.  开启权限后返回

@Override
public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    switch (requestCode) {
        case REQUEST_CODE:
            if (Environment.isExternalStorageManager()) {
                //有了权限 TODO
            }else {
                ToastUtil.showMessage("用户拒绝权限");
               
            }
            break;
        default:
            break;
    }
    super.onActivityResult(requestCode, resultCode, data);

}

到这里，文件读写权限就有了

下面为我的获取设备唯一不变id的代码

1 、 

public static String getDeviceId() {
    StringBuilder deviceId = new StringBuilder();
    // 渠道标志
    deviceId.append("a");
    try {

      
        TelephonyManager tm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
        String imeis;

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            imeis = tm.getImei();
        } else {
            imeis = tm.getDeviceId();
        }


        if (!TextUtils.isEmpty(imeis)) {
            deviceId.append("imei");
            deviceId.append(imeis);
            Log.e("getDeviceId : ", deviceId.toString());
            return deviceId.toString();
        }
        //序列号（sn）
        String sn = tm.getSimSerialNumber();
        if (!TextUtils.isEmpty(sn)) {
            deviceId.append("sn");
            deviceId.append(sn);
            Log.e("getDeviceId : ", deviceId.toString());
            return deviceId.toString();
        }
        //如果上面都没有， 则生成一个id：随机码
        String uuid = getUUID(context);
        if (!TextUtils.isEmpty(uuid)) {
            deviceId.append("sdid");
            deviceId.append(uuid);
            Log.e("getDeviceId : ", deviceId.toString());
            return deviceId.toString();
        }
    } catch (Exception e) {
        e.printStackTrace();
        deviceId.append("esdid").append(getUUID(context));
    }
    Log.e("getDeviceId : ", deviceId.toString());
    return deviceId.toString();
}

2. 

/**
 * 得到全局唯一UUID
 */
public static String getUUID() {
    try {
       String uuid = loadData();
        if (TextUtils.isEmpty(uuid)) {
            uuid = UUID.randomUUID().toString();
            saveData(uuid);
        }
        Log.e("tag", "getUUID : " + uuid);
        return uuid;
    } catch (IOException e) {
        e.printStackTrace();
    }
    return UUID.randomUUID().toString()+"catch";

}

3. 

private static final String FILENAME = "data.txt";

public static void saveData(String uuid) throws IOException {
  
      File sdCard = new File(getDownloadPath());
      FileOutputStream out = new FileOutputStream(sdCard);
      Writer writer = new OutputStreamWriter(out);
      try {
          writer.write(uuid);
      } finally {
          writer.close();
      }
  
}
public static String loadData() throws IOException {
    BufferedReader reader = null;
    StringBuilder data = new StringBuilder();
    Environment.getExternalStorageDirectory().getAbsolutePath();
    try {
        File sdCard = new File(getDownloadPath());
        FileInputStream in = new FileInputStream(sdCard);
        reader = new BufferedReader(new InputStreamReader(in));
        String line = new String();
        while ((line = reader.readLine()) != null) {
            data.append(line);
        }
        return data.toString();
    } catch (FileNotFoundException e) {
        return null;
    } finally {
        if (reader != null) {
            reader.close();
        }
      
    }
}

4. 

/**
     * sd卡获取下载路径
     * @return /storage/emulated/0/Download/
     */
    public static String getDownloadPath() {
        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            File file = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator + Environment.DIRECTORY_DOWNLOADS + File.separator + "MyFile/");
            if (!file.exists()) {
                file.mkdirs();
            }
            return Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator + Environment.DIRECTORY_DOWNLOADS + File.separator + "MyFile/"+ FILENAME;
        } else {

            String apkFilePath=Environment.getDataDirectory().getAbsolutePath() + File.separator + "local" +File.separator+"tmp"+File.separator+ "MyFile/" + FILENAME;
            String[] command = { "chmod", "777", apkFilePath };
            ProcessBuilder builder = new ProcessBuilder(command);
            try
            {
                builder.start();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
            File file = new File(Environment.getDataDirectory().getAbsolutePath() + File.separator + "local" +File.separator+"tmp"+File.separator+ "MyFile/");
            if (!file.exists()) {
                file.mkdirs();
            }
            return apkFilePath;
        }
    }