Android - 恢復數據庫在數據庫文件丟失時清除數據庫

Question

我找到了一個tutorial，它將數據庫作爲備份複製到文件夾，並將其作爲還原複製迴應用程序的數據庫文件夾。幾乎一切正常，除了一件事情：當我從我的文件夾中刪除已備份的.db文件，然後單擊應用程序中的還原時，它將查找該文件，找不到它，然後它將不會覆蓋整個數據庫。這就像我清空了整個數據庫。

備份：

try { 

        InputStream myInput; 
        OutputStream myOutput; 

        myInput = new FileInputStream("/data/data/com.me.myapp/databases/HotOrNotdbLists2");//this is 
     // the path for all apps 
     //insert your package instead packagename,ex:com.mybusiness.myapp 


        // Set the output folder on the SDcard 
        File directory = new File("/sdcard/MyApp/"); 
        // Create the folder if it doesn't exist: 
        if (!directory.exists()) 
        { 
         directory.mkdirs(); 
        } 
        // Set the output file stream up: 

        myOutput = new FileOutputStream(directory.getPath()+ 
     "/myapp.db"); 

        // Transfer bytes from the input file to the output file 
        byte[] buffer = new byte[1024]; 
        int length; 
        while ((length = myInput.read(buffer))>0) 
        { 
         myOutput.write(buffer, 0, length); 
        } 
        // Close and clear the streams 

        myOutput.flush(); 

        myOutput.close(); 

        myInput.close(); 
        Toast.makeText(Settings.this, "Backup done successfully!", Toast.LENGTH_LONG).show(); 

       } catch (FileNotFoundException e) { 
      Toast.makeText(Settings.this, "Backup unsuccessful! File cannot be created! Directory does not exist?", Toast.LENGTH_LONG).show(); 


        // TODO Auto-generated catch block 
        e.printStackTrace(); 
       } catch (IOException e) { 
      Toast.makeText(Settings.this, "Backup unsuccessful!", Toast.LENGTH_LONG).show(); 


        // TODO Auto-generated catch block 
        e.printStackTrace(); 
       } 

還原：

OutputStream myOutput; 

       try { 

        myOutput = new FileOutputStream("/data/data/com.me.myapp/databases/HotOrNotdbLists2"); 


        // Set the folder on the SDcard 
        File directory = new File("/sdcard/MyApp/"); 
        // Set the input file stream up: 

        InputStream myInputs = new FileInputStream(directory.getPath()+ "/myapp.db"); 


        // Transfer bytes from the input file to the output file 
        byte[] buffer = new byte[1024]; 
        int length; 
        while ((length = myInputs.read(buffer))>0) 
        { 
         myOutput.write(buffer, 0, length); 
        } 


        // Close and clear the streams 
        myOutput.flush(); 

        myOutput.close(); 

        myInputs.close(); 
        Toast.makeText(Settings.this, "Restore done successfully!", Toast.LENGTH_SHORT).show(); 

       } catch (FileNotFoundException e) { 
     Toast.makeText(Settings.this, "Restore unsuccessful! File not found! Directory does not exist?", Toast.LENGTH_LONG).show(); 


        // TODO Auto-generated catch block 
        e.printStackTrace(); 
       } catch (IOException e) { Toast.makeText(Settings.this, "Restore unsuccessful!", 
     Toast.LENGTH_SHORT).show(); 


        // TODO Auto-generated catch block 
        e.printStackTrace(); 
       } 

編輯： 我加了賈森的回答，它仍然會清除該數據庫，即使我得到假到directoryB並獲得恢復不成功！文件未找到！目錄/文件不存在？消息???！？！

try { 
         OutputStream myOutput; 
         myOutput = new FileOutputStream("/data/data/com.me.myapp/databases/HotOrNotdbLists2"); 

         // Set the folder on the SDcard 
         File directory = new File("/sdcard/MyApp/"); 
         boolean directoryB = new File("/sdcard/MyApp/", "/myapp.db").exists(); 
    Toast.makeText(Settings.this, "directoryB: " + directoryB, Toast.LENGTH_SHORT).show(); 

         if (directoryB == true) 
         { 
          Toast.makeText(Settings.this, "File exists!", Toast.LENGTH_SHORT).show(); 

         // Set the input file stream up: 

         InputStream myInputs = new FileInputStream(directory.getPath()+ "/myapp.db"); 


         // Transfer bytes from the input file to the output file 
         byte[] buffer = new byte[1024]; 
         int length; 
         while ((length = myInputs.read(buffer))>0) 
         { 
          myOutput.write(buffer, 0, length); 
         } 


         // Close and clear the streams 
         myOutput.flush(); 

         myOutput.close(); 

         myInputs.close(); 
         Toast.makeText(Settings.this, "Restore done successfully!", Toast.LENGTH_SHORT).show(); 
         } 
         else 
         { 
          Toast.makeText(Settings.this, "Restore unsuccessful! File not found! Directory/file does not exist?", Toast.LENGTH_SHORT).show(); 
         } 

        } catch (FileNotFoundException e) { 
      //Toast.makeText(Settings.this, "Restore unsuccessful! File not found! Directory does not exist?", Toast.LENGTH_LONG).show(); 


         // TODO Auto-generated catch block 
         e.printStackTrace(); 
        } catch (IOException e) { Toast.makeText(Settings.this, "Restore unsuccessful!", 
      Toast.LENGTH_SHORT).show(); 


         // TODO Auto-generated catch block 
         e.printStackTrace(); 
        } 

Answer 1

檢查文件是否存在第一繼續恢復操作，像這樣前：

new File(directory, "/myapp.db").exists() 

FileInputStream將自動創建文件，如果它們不存在。