0

我正在尝试这段代码：

http://androidgenuine.com/?tag=export-database-android

通过在我的示例中使用此代码，我总是得到一个FileNotFoundException，尽管在读取 FileInputStream 时该文件夹存在于外部存储中。

这是我的代码：

public void exportdata()
    {

        try 
        {

            myInput = new FileInputStream("/data/data/com.example.hello/databases/BikeMaintenance.db");
            File directory = new File("/sdcard/BikeMaintenance/Data/");
            // Create the folder if it doesn't exist:
            if (!directory.exists()) 
            {
                directory.mkdirs();
            } 

            OutputStream myOutput = new FileOutputStream(directory.getPath()+"/BikeMaintenance.backup");
            byte[] buffer = new byte[1024];
            int length;
            while ((length = myInput.read(buffer))>0)
            {

                myOutput.write(buffer, 0, length);
                msg="Backup Succesfull!";
                Toast.makeText(MainPage.this,msg,Toast.LENGTH_SHORT).show();
            }
            // Close and clear the streams
            myOutput.flush();
            myOutput.close();        
            myInput.close();
        }
        catch (FileNotFoundException e) 
        {
            msg="FileNotFoundException";
            Toast.makeText(MainPage.this,msg,Toast.LENGTH_SHORT).show();

            e.printStackTrace();
        } 
        catch (IOException e) 
        {
            msg="Backup Unsuccesfull!";
            Toast.makeText(MainPage.this,msg,Toast.LENGTH_SHORT).show();
        }

    }

我哪里错了？这可能是什么原因？我为此搜索了解决方案，但没有找到解决方案。

这是 logcat 输出：

java.io.FileNotFoundException:
/data/data/com.example.hello/databases/BikeMaintenance.db：打开
失败：ENOENT（没有这样的文件或目录）
  在 libcore.io.IoBridge.open(IoBridge.java:416)
  在 java.io.FileInputStream.(FileInputStream.java:78)
  在 java.io.FileInputStream.(FileInputStream.java:105)
  在 com.example.hello.MainPage.exportdata(MainPage.java:625)
  在 com.example.hello.MainPage.backup(MainPage.java:692)
  在 com.example.hello.MainPage$1.onClick(MainPage.java:494)
  在 com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
  在 android.os.Handler.dispatchMessage(Handler.java:99)
  在 android.os.Looper.loop(Looper.java:137)
  在 android.app.ActivityThread.main(ActivityThread.java:4745)
  在 java.lang.reflect.Method.invokeNative(Native Method)
  在 java.lang.reflect.Method.invoke(Method.java:511)
  在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
  在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
  在 dalvik.system.NativeStart.main（本机方法）
引起：libcore.io.ErrnoException：打开失败：
ENOENT（没有这样的文件或目录）
  在 libcore.io.Posix.open（本机方法）
  在 libcore.io.BlockGuardOs.open(BlockGuardOs.java:110)
  在 libcore.io.IoBridge.open(IoBridge.java:400)
  ... 14 更多
4

2 回答 2

1

您的代码对我来说看起来不错，但我认为您无权访问该 .db 文件您可以使用 DataBaseHelper 类访问您的 .db 文件

    public class DataBaseHelper extends SQLiteOpenHelper {

     private static String DB_PATH = "/data/data/com.android.electricbillgenerator/databases/";

        private static String DB_NAME = "BikeMaintenance.db";

        private SQLiteDatabase myDataBase;

        private Context myContext;

        public static final String COLUMN_ID = "_id";
        public static final String COLUMN_USERNAME = "UserName";
        public static final String COLUMN_PASSWORD = "Password";
        public static final String TABLE_NAME = "Login";
        private static final String DATABASE_NAME = "BikeMaintenance.db";
        private static final int DATABASE_VERSION = 1;

     // Database creation sql statement
//      private static final String DATABASE_CREATE = "create table "
//          + TABLE_NAME + "(" + COLUMN_ID
//          + "," + COLUMN_USERNAME
//          + "," + COLUMN_PASSWORD+ ");";

//      private static final String DATABASE_CREATE = "create table "
//              + TABLE_NAME + "(" + COLUMN_ID
//              + " integer primary key autoincrement, " + COLUMN_USERNAME
//              + " text not null," + COLUMN_PASSWORD+ "text not null);";

    public DataBaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 8);
        this.myContext = context;

         boolean dbexist = checkDataBase();
            if (dbexist) {
                //System.out.println("Database exists");
                openDataBase(); 
            } else {
                System.out.println("Database doesn't exist");
                try {
                    createDataBase();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

    }


    @Override
    public void onCreate(SQLiteDatabase database) {



//      try {
//          database.execSQL(DATABASE_CREATE);
//      } catch (SQLException e) {
//          // TODO Auto-generated catch block
//          e.printStackTrace();
//      }

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//      Log.w(DataBaseHelper.class.getName(),
//              "Upgrading database from version " + oldVersion + " to "
//                  + newVersion + ", which will destroy all old data");
//          db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
//          onCreate(db);

    }




    /**
     * Creates a empty database on the system and rewrites it with your own database.
     * */
    public void createDataBase() throws IOException{

        boolean dbExist = checkDataBase();

        if(dbExist){
            //do nothing - database already exist
        }else{

            //By calling this method and empty database will be created into the default system path
               //of your application so we are gonna be able to overwrite that database with our database.
            this.getReadableDatabase();

            try {

                copyDataBase();

            } catch (IOException e) {

                throw new Error("Error copying database");

            }
        }

    }


    /**
     * Check if the database already exist to avoid re-copying the file each time you open the application.
     * @return true if it exists, false if it doesn't
     */
    private boolean checkDataBase(){

        SQLiteDatabase checkDB = null;

        try{
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

        }catch(SQLiteException e){

            //database does't exist yet.

        }

        if(checkDB != null){

            checkDB.close();

        }

        return checkDB != null ? true : false;
    }

    /**
     * Copies your database from your local assets-folder to the just created empty database in the
     * system folder, from where it can be accessed and handled.
     * This is done by transfering bytestream.
     * */
    private void copyDataBase() throws IOException{

        //Open your local db as the input stream
        InputStream myInput = myContext.getAssets().open(DB_NAME);

        // Path to the just created empty db
        String outFileName = DB_PATH + DB_NAME;

        //Open the empty db as the output stream
        OutputStream myOutput = new FileOutputStream(outFileName);

        //transfer bytes from the inputfile to the outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer))>0){
            myOutput.write(buffer, 0, length);
        }

        //Close the streams
        myOutput.flush();
        myOutput.close();
        myInput.close();

    }
    public void openDataBase() throws SQLException{

        //Open the database
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

    }

    @Override
    public synchronized void close() {

            if(myDataBase != null)
                myDataBase.close();

            super.close();

    }



}
于 2013-04-07T16:03:15.103 回答
0

来自 Android 文档

public FileInputStream (File file)

Constructs a new FileInputStream that reads from file.

Parameters
file    the file from which this stream reads.
Throws
FileNotFoundException   if file does not exist.

您谈论存在的文件夹，但错误与文件有关。仔细检查文件是否真的存在，也许用 adb

$ adb shell ls /data/data/com.example.hello/databases/BikeMaintenance.db

或包含目录的权限。

于 2013-04-07T15:20:40.603 回答