java - 打开 Sqlite DB Android 时出现 FileNotFound 异常

Question

我正在尝试在我的 Android 项目上打开现有的 sqlite 数据库，但第二次运行时出现 Filenotfound 异常，第一次运行时出现其他错误。

public class SyllabusHelper extends SQLiteOpenHelper {
    private static Context mContext;
    public static final String DB_NAME="dusyllabus";
    public static String DB_LOCATION= "/data/data/com.example.amalaugustine.dusyllabus/databases/";
    private static int DB_VERSION=1;
    private SQLiteDatabase mDB;
public SyllabusHelper(Context context) {
    super(context,DB_NAME,null,1);
    ContextWrapper cw =new ContextWrapper(context);
    DB_LOCATION=cw.getFilesDir().getAbsolutePath()+ "/databases/";
    Log.v("DBLOCATIONA",DB_LOCATION);
    this.mContext = context;
    copyDatabase(mContext);
}
public void OpenDatabase(){
    String dbPath=mContext.getDatabasePath(DB_NAME).getPath();
    Log.v("dbpatH",dbPath.toString());
   if(mDB!=null && mDB.isOpen()){
        return;
    }
mDB=SQLiteDatabase.openDatabase(DB_LOCATION,null,SQLiteDatabase.OPEN_READWRITE);
    }



private boolean copyDatabase(Context context) {
        Log.i("Database",
                "New database is being copied to device!");
        byte[] buffer = new byte[1024];
        OutputStream myOutput = null;
        int length;
        // Open your local db as the input stream
        InputStream myInput = null;
        try {
            myInput = context.getAssets().open(DB_LOCATION + DB_NAME);
            // transfer bytes from the inputfile to the
            // outputfile
            myOutput = new FileOutputStream(DB_LOCATION + DB_NAME);
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }
            myOutput.close();
            myOutput.flush();
            myInput.close();
            Log.i("Database",
                    "New database has been copied to device!");
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            Log.v("QuizActivity", e.toString());
            return false;

        }
    }

上面的代码是在android上打开一个现有的sqlite数据库，当我运行代码时，我在logcat上收到一个错误，如下

10-12 13:50:10.389 9813-9813/com.example.amalaugustine.dusyllabus E/HAL: PATH3 /odm/lib64/hw/gralloc.qcom.so
    PATH2 /vendor/lib64/hw/gralloc.qcom.so
    PATH1 /system/lib64/hw/gralloc.qcom.so
    PATH3 /odm/lib64/hw/gralloc.msm8953.so
    PATH2 /vendor/lib64/hw/gralloc.msm8953.so
    PATH1 /system/lib64/hw/gralloc.msm8953.so

当我打开运行的应用程序时，它崩溃了，logcat 上的错误是 filenotfound 异常。我正在尝试打开 Assets 内数据库文件夹中的现有数据库，但无法打开该数据库，可能的错误是什么？我无法找出确切的错误，如果有人可以帮助我编写可从 Assets 文件夹打开现有数据库的代码，谢谢。

Answer 1

我相信找不到文件异常的原因是因为您正在使用:-

myInput = context.getAssets().open(DB_LOCATION + DB_NAME);

这将尝试在 Assets 文件夹中查找名为 /data/user/0/amalaugustine.example.com.dusyllabus/files/databases/dusyllabus 的文件。

您可能应该只查找数据库文件，所以

myInput = context.getAssets().open(DB_NAME);

假设名为dusyllabus的文件不在assets文件夹的子目录中，而是直接位于assets文件夹中。

但是，您会遇到问题

myOutput = new FileOutputStream(DB_LOCATION + DB_NAME);

因为，除非该文件存在，否则会发生第二个文件未找到异常。

此外，您使用的路径不正确，而不是 /data/user/0/amalaugustine.example.com.dusyllabus/files/databases/dusyllabus

路径实际上应该是/data/user/0/amalaugustine.example.com.dusyllabus/databases/dusyllabus

此外，您尝试使用的代码将导致每次创建 SyllabusHelper 类的实例时从 Assets 文件中复制数据库。因为没有检查数据库当前是否存在。

建议完整修复:-

我建议为SyllabusHelper.java使用以下代码:-

public class SyllabusHelper extends SQLiteOpenHelper {
    private static Context mContext;
    public static final String DB_NAME = "dusyllabus";
    //public static String DB_LOCATION = "/data/data/com.example.amalaugustine.dusyllabus/databases/"; //<<<<<<<<<< not needed
    public String db_location; //<<<<<<<<<< ADDED
    private static int DB_VERSION = 1;
    private SQLiteDatabase mDB;

    public SyllabusHelper(Context context) {
        super(context, DB_NAME, null, 1);
        //ContextWrapper cw = new ContextWrapper(context); //<<<<<<<<<< NOT NEEDED
        //DB_LOCATION = cw.getFilesDir().getAbsolutePath() + "/databases/"; //<<<<<<<<<<WRONG
        db_location = context.getDatabasePath(DB_NAME).getPath(); //<<<<<<<<<< recommended way to get the path
        //Log.v("DBLOCATIONA", DB_LOCATION); //<<<<<<<<<< not used
        Log.v("DBLOCATIONB",db_location); //<<<<<<<<<< changed
        this.mContext = context;
        copyDatabase(mContext);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        Log.v("ONCREATE","On Create has been called");
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }

    public void OpenDatabase() {
        String dbPath = mContext.getDatabasePath(DB_NAME).getPath();
        Log.v("dbpatH", dbPath.toString());
        if (mDB != null && mDB.isOpen()) {
            return;
        }
        mDB = this.getWritableDatabase();
    }


    private boolean copyDatabase(Context context) {
        if (doesDBExist()) return true; //<<<<<<<<<< Check if database already exists
        Log.i("Database",
                "New database is being copied to device!");
        byte[] buffer = new byte[1024];
        OutputStream myOutput = null;
        int length;
        // Open your local db as the input stream
        InputStream myInput = null;
        try {
            myInput = context.getAssets().open(DB_NAME); //<<<<<<<<<< only get according to the file name not the path
            // transfer bytes from the inputfile to the
            // outputfile
            File newdb = new File(db_location); //<<<<<<<<<< get the file so that it exists
            myOutput = new FileOutputStream(newdb); //<<<<<<<<<< uses the file
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }
            myOutput.close();
            myOutput.flush();
            myInput.close();
            Log.i("Database",
                    "New database has been copied to device!");
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            Log.v("QuizActivity", e.toString());
            return false;
        }
    }

    //<<<<<<<<<<< ADDED to check for existence of db file
    //!!NOTE!! does not check that the file is a valid database
    private boolean doesDBExist() {
        File db = new File(db_location);
        if (db.exists()) {
            return true;
        }
        File dbdir =  new File(db.getParent());
        dbdir.mkdirs();
        return false;
    }
}

当然，您始终可以使用 SQLiteAssetHelper