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Q:SQLite Database storage in /data/data Android

Q:SQLite数据库存储/数据/数据Android

I have one sqlite database stored in an "assets" folder and I'd like to store it into /data/data folder within the Android device. It's just a readonly db from which I want to retrieve data.

I've been reading a lot of topics talking about that but when I check the /data/data/ folder in my device, my package isn't there. Here's the code I've been using:

public class DatabaseManager extends SQLiteOpenHelper {
private static final String TAG = "DataBaseManager";

private static String DB_PATH = "/data/data/com.my_package/databases/";
private static String DB_NAME = "my_database";
public SQLiteDatabase myDataBase;
private final Context myContext;

/**
 * Constructor
 * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
 * @param context
 */
public DatabaseManager(Context context) {

    super(context, DB_NAME, null, 1);
    this.myContext = context;
    try {
        createDataBase();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

/**
 * 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
        Log.d("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.getWritableDatabase();

        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){
        Log.d("DATABASE", "DOESNT EXIST");
    }

    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[2048];
    int length;
    while ((length = myInput.read(buffer))>0){
        myOutput.write(buffer, 0, length);
    }

    //Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();
    Log.d("COPY DATABASE", "DATABASE COPIED");
}

public void openDataBase() throws SQLException {
    //Open the database
    String myPath = DB_PATH + DB_NAME;
    myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
    Cursor cursor = myDataBase.rawQuery("SELECT * FROM chapters", null);

    while (cursor.moveToNext()) {
        cursor.getString(3);
        Log.d("CONTENT", cursor.getString(3));
    }

    myDataBase.beginTransaction();
}

@Override
public synchronized void close() {

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

    super.close();

}

@Override
public void onCreate(SQLiteDatabase db) {

}

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

}

Thanks to the Log.d() messages, I can see the following message : "database already exists" (message from createDatabase method) and yet, I have no data in the /data/data folder of my Android device.

This seems strange to me because in checkDatabase method, I check if a database exists in myPath variable, variable whose value corresponds to DB_PATH and DB_NAME, namely the /data/data folder and, like I said, I opened the internal memory of my device and checked if something was created in the /data/data folder but nothing.

我有一个SQLite数据库存储在一个“资产”的文件夹,我想把它存放到/数据/数据的Android设备内的文件夹。这只是一个只读数据库,我想检索数据。

我一直在阅读很多话题,但当我检查/数据/数据/文件夹在我的设备,我的包不存在。这里是我一直使用的代码:

public class DatabaseManager extends SQLiteOpenHelper {
private static final String TAG = "DataBaseManager";

private static String DB_PATH = "/data/data/com.my_package/databases/";
private static String DB_NAME = "my_database";
public SQLiteDatabase myDataBase;
private final Context myContext;

/**
 * Constructor
 * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
 * @param context
 */
public DatabaseManager(Context context) {

    super(context, DB_NAME, null, 1);
    this.myContext = context;
    try {
        createDataBase();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

/**
 * 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
        Log.d("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.getWritableDatabase();

        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){
        Log.d("DATABASE", "DOESNT EXIST");
    }

    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[2048];
    int length;
    while ((length = myInput.read(buffer))>0){
        myOutput.write(buffer, 0, length);
    }

    //Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();
    Log.d("COPY DATABASE", "DATABASE COPIED");
}

public void openDataBase() throws SQLException {
    //Open the database
    String myPath = DB_PATH + DB_NAME;
    myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
    Cursor cursor = myDataBase.rawQuery("SELECT * FROM chapters", null);

    while (cursor.moveToNext()) {
        cursor.getString(3);
        Log.d("CONTENT", cursor.getString(3));
    }

    myDataBase.beginTransaction();
}

@Override
public synchronized void close() {

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

    super.close();

}

@Override
public void onCreate(SQLiteDatabase db) {

}

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

}

由于日志。d()消息,我可以看到以下信息:“数据库已存在”(从CreateDatabase方法消息)然而,我没有数据/数据/数据我的Android设备文件夹。

这似乎很奇怪,我因为在checkdatabase方法,我检查一个数据库存在于建立变量,变量的值对应于db_path和db_name,即/数据/数据文件夹,就像我说的,我打开我的设备内存和检查,如果事情是创建于/数据/数据文件夹,但没有什么。

answer1: 回答1:

I think you hav to change the DB_NAME variable from "my_database" to "my_database.sqlite"

and u cant see your database on your internal memory... bcoz the database will save only to the system folder... if u want to check it u might need a rooted android device or you can check using android studio...

check this link... check database if exist in android studio

我想你要的db_name变量从“my_database”转变为“my_database。SQLite”

and u cant see your database on your internal memory... bcoz the database will save only to the system folder... if u want to check it u might need a rooted android device or you can check using android studio...

检查此链接…检查数据库是否存在Android工作室

answer2: 回答2:

Better to check DB File like

 public boolean checkDataBase(){
    File databaseFile = new File(DB_PATH + DB_NAME);
    return databaseFile.exists();        
}

更好地检查DB文件

 public boolean checkDataBase(){
    File databaseFile = new File(DB_PATH + DB_NAME);
    return databaseFile.exists();        
}
answer3: 回答3:

SQLiteDatabase.openDatabasewill automatically create the DB if it doesn't exists (see CREATE_IF_NECESSARYflag).

In general, you must first copy the embedded databse from asset directory to your application data directory : data/data/com.my_package/databases.

Then you can use your database.

See SQLiteAssetHelper if necessary: https://github.com/jgilfelt/android-sqlite-asset-helper

sqlitedatabase.opendatabasewill自动创建数据库如果不存在(见create_if_necessaryflag)。

总的来说,你首先必须将嵌入式数据库从资产目录到你的应用程序数据目录:数据/数据/ com.my_package/databases。

然后你可以使用你的数据库。

如果需要看sqliteassethelper:https://github.com/jgilfelt/android-sqlite-asset-helper

android  sqlite