无法从资产中复制 SQLite 数据库

Question

我尝试从 assets 目录中复制 SQLite 数据库以便稍后访问它。但我做不到！

public class DatabaseAdapter {
    private static String DB_PATH = "/data/data/com.mypackage/databases/";
    private static String DB_NAME = "database.sqlite";
    private static String TABLE_NAME = "content_table";

    private SQLiteDatabase database = null;
    private final Context context;

    public DatabaseAdapter(Context context){
        this.context = context;
    }

    private void openDatabase() throws SQLiteException{
        DatabaseHelper databaseHelper = new DatabaseHelper(context, DB_NAME);
        SQLiteDatabase db = null;
        if(!checkDatabase()){
            try{
                //Tried to create db before copying, so file should exist
                db = databaseHelper.getReadableDatabase();
                db.close();

                copyDatabase();

            }catch(IOException exception){
                Log.d("DatabaseAdapter", "Error copying DB: "+exception);
            }
        }

        database = SQLiteDatabase.openDatabase(DB_PATH+DB_NAME, null, SQLiteDatabase.OPEN_READONLY);
    }

    private void closeDatabase(){
        database.close();
    }

    public ArrayList<String> queryCategories(){
        try{
            openDatabase();
        }catch(SQLiteException exc){
            exc.printStackTrace();
        }
        //.............................
        return result;
    }

    private boolean checkDatabase(){
        File dbFile = new File(DB_PATH + DB_NAME);
        return dbFile.exists();
    }

    private void copyDatabase() throws IOException{
        InputStream inputStream = context.getAssets().open(DB_NAME);

        String outFileName = DB_PATH + DB_NAME;

        OutputStream outputStream = new FileOutputStream(outFileName);

        byte[] buffer = new byte[1024];
        int length;
        while ((length = inputStream.read(buffer))>0){
            outputStream.write(buffer, 0, length);
        }

        outputStream.flush();
        outputStream.close();
        inputStream.close();
    }

}

DatabaseHelper 很简单：

ublic class DatabaseHelper extends SQLiteOpenHelper {

    public DatabaseHelper(Context context, String name){
        super(context, name, null, 1);

    }


    @Override
    public void onCreate(SQLiteDatabase arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub

    }

}

什么都试过了！我试过玩扩展！但我仍然得到一个错误： 复制数据库时出错：java.io.FileNotFoundException: /data/data/com.mypackage/databases/database.sqlite (No such file or directory)

我检查了模拟器，我的文件在那里，所以我应该可以写入它！ 请，任何帮助！快把我逼疯了！

UPD 我尝试将它放在 SD 卡上，它可以工作。但还是不明白为什么我不能将它写入应用数据文件夹。

Answer 1

我使用这个 Helper 并且工作正常：

public class DBHelper extends SQLiteOpenHelper{

private final static String DB_PATH = "/data/data/[YOUR PACKAGE HERE]/databases/";

String dbName;
Context context;

File dbFile;

public DBHelper(Context context, String dbName, CursorFactory factory,
        int version) {
    super(context, dbName, factory, version);
    this.context = context;
    this.dbName = dbName;
    dbFile= new File(DB_PATH + dbName);
}

@Override
public synchronized SQLiteDatabase getWritableDatabase() {

    if(!dbFile.exists()){
        SQLiteDatabase db = super.getWritableDatabase();
        copyDataBase(db.getPath());
    }
    return super.getWritableDatabase();
}

@Override
public synchronized SQLiteDatabase getReadableDatabase() {
    if(!dbFile.exists()){
        SQLiteDatabase db = super.getReadableDatabase();
        copyDataBase(db.getPath());
    }
    return super.getReadableDatabase();
}

@Override
public void onCreate(SQLiteDatabase db) {}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}

private void copyDataBase(String dbPath){
    try{
        InputStream assestDB = context.getAssets().open("databases/"+dbName);

        OutputStream appDB = new FileOutputStream(dbPath,false);

        byte[] buffer = new byte[1024];
        int length;
        while ((length = assestDB.read(buffer)) > 0) {
            appDB.write(buffer, 0, length);
        }

        appDB.flush();
        appDB.close();
        assestDB.close();
    }catch(IOException e){
        e.printStackTrace();
    }

}

}

考虑到数据库的文件扩展名是 .db 并且我的数据库位于 assets/databases/

Answer 2

我有同样的问题，我已经用另一种方法解决了它。 一开始我和大家一样声明了数据库路径：

dbPath="data/data/<my package name>/databases/data.db"

这是一条准确的路径，没错。但是当我尝试打开 OutPutFileStream 来复制数据库时，它总是失败。我不知道为什么。然后，我改变了打开数据库的方式如下：

dbPath = context.getDatabasePath(dbName);
OutputStream myOutput = new FileOutputStream(dbPath.getAbsolutePath());

问题已解决。太惊喜了。

希望这会有所帮助。

Answer 3

public static void copyDatabase(final Context ctx, String dbName) {
    if (ctx != null) {
        File f = ctx.getDatabasePath(dbName);
        if (!f.exists()) {

            // check databases exists
            if (!f.getParentFile().exists())
                f.getParentFile().mkdir();

            try {
                InputStream in = ctx.getAssets().open(dbName);
                OutputStream out = new FileOutputStream(f.getAbsolutePath());

                byte[] buffer = new byte[1024];
                int length;
                while ((length = in.read(buffer)) > 0) {
                    out.write(buffer, 0, length);
                }
                in.close();
                out.close();
                Logger.i("Database copy successed! " + f.getPath());
            } catch (Exception ex) {
                Logger.e(ex);
            }
        }
    }
}

Answer 4

请检查您的 OutputStream 之前的数据库文件夹。

像这样，

File databaseFile = new File(context.getFilesDir().getAbsolutePath()
            .replace("files", "databases"));

// check if databases folder exists, if not create it.
if (!databaseFile.exists()){
    databaseFile.mkdir();
}