Question

为此，我找不到合适的解决方案。甚至我都不知道如何在房间数据库中备份和还原备份文件。请帮我怎么做。

我没有任何疑问，但是堆栈溢出给我错误，这就是为什么我写这行代码的原因

我找到了备份的方法，但找不到还原数据库的解决方案当我检查应用程序是否显示还原成功，但应用程序中不存在真实数据时

 public static boolean backUpDatabase(Context context) throws IOException {
        db.close();
        File dbFile = new File(String.valueOf(context.getDatabasePath(MainDatabase.DATABASE_NAME)));
        File sDir = new File(Environment.getExternalStorageDirectory().getAbsolutePath(),"Tuition App2");
        String fileName = "TuitionApp_BackUp.db";
        String sfPath = sDir.getAbsolutePath()+"/"+fileName;
        if (!sDir.exists()){
            sDir.mkdirs();
        }
        File saveFile = new File(sfPath);
        if (saveFile.exists()){
            saveFile.delete();
        }
        if (saveFile.createNewFile()){
            int bufferSize = 8 * 1024;
            byte[] buffer = new byte[bufferSize];
            int bytes_read = bufferSize;
            OutputStream saveDb = new FileOutputStream(sfPath);
            InputStream inDb = new FileInputStream(dbFile);
            while ((bytes_read = inDb.read(buffer, 0, bufferSize)) > 0) {
                saveDb.write(buffer, 0, bytes_read);
            }
            saveDb.flush();
            inDb.close();
            saveDb.close();
//saving path in to sharedPraf  sm is object of that class
            sm.saveBackFileName(context,sfPath);
            return true;
        }
        return false;
    }
    public static boolean restoreDataBase(Context context) throws FileNotFoundException {
        db.close();
        File sDir = new File(sm.getBackupFileName(context));
        File finalFile = new File(sDir.getAbsolutePath());
        InputStream inputStream = context.getContentResolver().openInputStream(Uri.fromFile(finalFile));
        File oldDb = context.getDatabasePath(MainDatabase.DATABASE_NAME);
        if ( inputStream!= null){
            try {
                copyFile((FileInputStream) inputStream,new FileOutputStream(oldDb));
                return true;
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return false;
    }
    public static void copyFile(FileInputStream fromFile, FileOutputStream toFile) throws IOException {
        FileChannel fromChannel = null;
        FileChannel toChannel = null;
        try {
            fromChannel = fromFile.getChannel();
            toChannel = toFile.getChannel();
            fromChannel.transferTo(0, fromChannel.size(), toChannel);

        } finally {
            try {
                if (fromChannel != null) {
                    fromChannel.close();
                }
            } finally {
                if (toChannel != null) {
                    toChannel.close();
                }
            }
        }
    }

Answer 1

这是使用SQLite的，但是过程应该相同：

https://medium.com/@gavingt/refactoring-my-backup-and-restore-feature-to-comply-with-scoped-storage-e2b6c792c3b

下面的内容还将向您展示如何遵守作用域存储，因为您的操作方式现在在Android 11上根本无法使用：

https://developer.android.com/preview/privacy/storage

您可能还想禁用onOpen()中的预写日志记录。这就是SQLite中的样子：

    @Override
public void onOpen(SQLiteDatabase db) {
    super.onOpen(db);
    //disable write-ahead logging to make backup/restore work on all devices.
    db.disableWriteAheadLogging();
}

请参见以下链接，以将onOpen()回调放在Room中的位置：

https://medium.com/@srinuraop/database-create-and-open-callbacks-in-room-7ca98c3286ab

如何轻松恢复会议室数据库中的备份文件？

1 个答案: