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

public class PermisionUtils {

 // Storage Permissions
 private static final int REQUEST_EXTERNAL_STORAGE = 1;
 private static String[] PERMISSIONS_STORAGE = {
   Manifest.permission.READ_EXTERNAL_STORAGE,
   Manifest.permission.WRITE_EXTERNAL_STORAGE};

 /**
  * Checks if the app has permission to write to device storage
  * If the app does not has permission then the user will be prompted to
  * grant permissions
  *
  * @param activity
  */
 public static void verifyStoragePermissions(Activity activity) {
  // Check if we have write permission
  int permission = ActivityCompat.checkSelfPermission(activity,
    Manifest.permission.WRITE_EXTERNAL_STORAGE);

  if (permission != PackageManager.PERMISSION_GRANTED) {
   // We don't have permission so prompt the user
   ActivityCompat.requestPermissions(activity, PERMISSIONS_STORAGE,
     REQUEST_EXTERNAL_STORAGE);
  }
 }
}

 //檢測讀寫權限
 PermisionUtils.verifyStoragePermissions(this);