1

我找到了一个将数据库复制到文件夹作为备份并将其复制回应用程序的数据库文件夹作为恢复的教程。几乎一切正常，除了一件事：当我从我的文件夹中删除备份的 .db 文件并在我的应用程序中单击“恢复”时，它会查找该文件，找不到它，然后它会覆盖整个数据库，什么都没有。这就像我清空了整个数据库。

备份：

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();
                }

恢复：

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();
                }

编辑：我添加了杰森的答案，它仍然清除了数据库，即使我对 directoryB错误并且恢复不成功！文件未找到！目录/文件不存在？信息 ？？？！？！

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();
                    }
4

1 回答 1

1

在继续还原操作之前先检查文件是否存在，如下所示：

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

FileInputStream如果文件不存在，将自动创建文件。

于 2012-05-02T18:47:49.153 回答