String[] PERMISSIONS = {
    "android.permission.READ_EXTERNAL_STORAGE",
    "android.permission.WRITE_EXTERNAL_STORAGE" };
//檢測是否有寫的權(quán)限
int permission = ContextCompat.checkSelfPermission(this,
    "android.permission.WRITE_EXTERNAL_STORAGE");
if (permission != PackageManager.PERMISSION_GRANTED) {
  // 沒有寫的權(quán)限，去申請寫的權(quán)限，會彈出對話框
  ActivityCompat.requestPermissions(this, PERMISSIONS,1);
}
保存文件的方法：
public void SaveBitmapFromView(View view) {
  int w = view.getWidth();
  int h = view.getHeight();
  Bitmap bmp = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
  Canvas c = new Canvas(bmp);
  view.layout(0, 0, w, h);
  view.draw(c);
 // 縮小圖片
 Matrix matrix = new Matrix();
 matrix.postScale(0.5f,0.5f); //長和寬放大縮小的比例
 bmp = Bitmap.createBitmap(bmp,0,0,        bmp.getWidth(),bmp.getHeight(),matrix,true);
 DateFormat format = new SimpleDateFormat("yyyyMMddHHmmss"); 
  saveBitmap(bmp,format.format(new Date())+".JPEG");
}
/*
 * 保存文件，文件名為當(dāng)前日期
 */
Public void saveBitmap(Bitmap bitmap, String bitName){
    String fileName ;
    File file ;
    if(Build.BRAND .equals("Xiaomi") ){ // 小米手機 
      fileName = Environment.getExternalStorageDirectory().getPath()+"/DCIM/Camera/"+bitName ;
    }else{ // Meizu 、Oppo
      fileName = Environment.getExternalStorageDirectory().getPath()+"/DCIM/"+bitName ;
    }
    file = new File(fileName);
    if(file.exists()){
      file.delete();
    }
    FileOutputStream out;
    try{
      out = new FileOutputStream(file);
 // 格式為 JPEG，照相機拍出的圖片為JPEG格式的，PNG格式的不能顯示在相冊中
      if(bitmap.compress(Bitmap.CompressFormat.JPEG, 90, out))
      {
        out.flush();
        out.close();
// 插入圖庫  
         MediaStore.Images.Media.insertImage(this.getContentResolver(), file.getAbsolutePath(), bitName, null);
      }
    }
    catch (FileNotFoundException e)
    {
      e.printStackTrace();
    }
    catch (IOException e)
    {
      e.printStackTrace();
    }
 // 發(fā)送廣播，通知刷新圖庫的顯示
    this.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + fileName)));
}