从资产文件夹复制数据库[重复]

【问题标题】：Copy database from assets folder [duplicate]从资产文件夹复制数据库[重复]
【发布时间】：2014-01-21 06:10:02
【问题描述】：

我正在创建一个使用现有 sqlite 数据库的 Dictionary 应用程序。我已将我的数据库放在 assets 文件夹中，并在第一次启动应用程序时使用以下代码复制数据库。 （我从this帖子中借用了这个想法）

DatabaseHelper.java

public class DatabaseHelper {

private static String DB_PATH = "";
private static String DB_NAME = "abc.sqlite";
private SQLiteDatabase myDatabase;
private Context myContext;

public DatabaseHelper(Context context) {

    myContext = context;

    if (android.os.Build.VERSION.SDK_INT >= 17)
        DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
    else
        DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
    Log.d("path", DB_PATH);
}

public void copyDatabase() {

        InputStream myInput;
        OutputStream outStream;
        try {
            myInput = myContext.getAssets().open(DB_NAME);
            String file = DB_PATH + DB_NAME;
            outStream = new FileOutputStream(file);

            byte[] buffer = new byte[1024];
            int length = 0;
            while ((length = myInput.read(buffer)) >= 0) {
                outStream.write(buffer, 0, length);             
            }
            outStream.flush();
            myInput.close();
            outStream.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

然后我从我的MainActivity 中调用上述copyDatabase() 方法。这是代码。

public class MainActivity extends Activity {
    DatabaseHelper myDbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.layout);
        myDbHelper = new DatabaseHelper(getApplicationContext());
        myDbHelper.copyDatabase();


    }

}

但问题是Android不会复制数据库。我使用了 Log 工具，我发现 while 循环永远不会运行。 这段代码有什么问题。 谢谢。

【问题讨论】：

  • 只需将您的while循环行更改为while ((length = myInput.read(buffer)) > 0) {只需将其与>而不是>=进行比较。
  • 你继续使用 GrlsHu，您还需要在转到 FileOutputStream 之前创建文件
  • 在 SO 和其他地方有十几个这样的例子。应该用谷歌搜索。
  • @Rajat 记住从其他来源获取代码时的小错误。查看我的答案。

标签： android sqlite java-io


【解决方案1】：

改变你的while循环如下：

除了你的条件>=大于等于改成只有>大于

while ((length = myInput.read(buffer)) > 0) {
            outStream.write(buffer, 0, length);             
        }

试试下面的代码，它会像魅力一样为你工作。

public class DataBaseHelper extends SQLiteOpenHelper {
    private Context mycontext;
    private String DB_PATH; 

    private static String DB_NAME = "abc.sqlite";
    public SQLiteDatabase myDataBase;


    public DataBaseHelper(Context context) throws IOException {
        super(context,DB_NAME,null,1);
        this.mycontext=context;
        boolean dbexist = checkdatabase();
        if (dbexist) {
              opendatabase(); 
        } else {
            System.out.println("Database doesn't exist");
            createdatabase();
        }
    }

    public void createdatabase() throws IOException {
        boolean dbexist = checkdatabase();
        if(!dbexist) {
            this.getReadableDatabase();
            try {
                copydatabase();
            } catch(IOException e) {
                throw new Error("Error copying database");
            }
        }
    }   

    private boolean checkdatabase() {

        boolean checkdb = false;
        try {
            String myPath = DB_PATH + DB_NAME;
            File dbfile = new File(myPath);
            checkdb = dbfile.exists();
        } catch(SQLiteException e) {
            System.out.println("Database doesn't exist");
        }
        return checkdb;
    }

    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 byte to inputfile to 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_READWRITE);
    }

    public synchronized void close() {
        if(myDataBase != null) {
            myDataBase.close();
        }
        super.close();
    }

}

在您的MainActivity 中，您现在需要创建和实例化您的DatabaseHelper 类，其他人将自行管理。 

public class MainActivity extends Activity {
    DatabaseHelper myDbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.layout);
        myDbHelper = new DatabaseHelper(MainActivity.this);
      }

}

【讨论】：

  • 您好，感谢您的回复。但是代码还是不行。
  • @Rajat 你试过调试你的代码吗？显示你在哪里调用copyDatabase 方法？
  • 我已经添加了 MainActivity.java 代码。请检查。谢谢
  • 查看我的更新答案。并尝试它会为你工作的代码。您尝试的方式将行不通。您需要对数据库可用性进行一些检查。
  • 这是因为>= 将比较您指定的确切大小，不小于或不大于该大小。所以你写了>=0，这意味着如果它为零，那么它不会执行循环。
【解决方案2】：

改变这个

while ((length = myInput.read(buffer)) >= 0) {
            outStream.write(buffer, 0, length);             
        }

到

while ((length = myInput.read(buffer)) >0) {
            outStream.write(buffer, 0, length);             
        }

在 oncreate() 方法上复制数据库会更好，因为在您的课程中您已经这样做了。你必须在你的活动中调用你的数据库类对象并从中获取数据。所以首先创建一个名为 DBConnect

的类 
public class DBConnect extends SQLiteOpenHelper {
public int GetCursor;
// ****************** Declare all the global variable
// ****************************//
private Context myContext;
public String DB_PATH = "data/data/com.xyz/databases/"; // path
// of
// your
// datbase
public static String DB_NAME = "xyz.sqlite";// your database name
static String ASSETS_DB_FOLDER = "db";
private SQLiteDatabase db;

public DBConnect(Context context, String db_name) {
    super(context, db_name, null, 2);
    if (db != null && db.isOpen())
        close();

    this.myContext = context;
    DB_NAME = db_name;

    try {
        createDataBase();
        openDataBase();
    } catch (IOException e) {
        // System.out.println("Exception in creation of database : "+
        // e.getMessage());
        e.printStackTrace();
    }

}

public void createDataBase() throws IOException {
    boolean dbExist = checkDataBase();

    if (dbExist) {
        // System.out.println("Database Exist");
    } else {
        this.getReadableDatabase();

        try {
            copyDatabase();
        } catch (IOException e) {
            throw new Error("Error copying database");
        }
    }
}

private void copyDatabase() throws IOException {
    InputStream input = myContext.getAssets().open(DB_NAME);
    String outputFileName = DB_PATH + DB_NAME;
    OutputStream output = new FileOutputStream(outputFileName);

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

    // Close the streams
    output.flush();
    output.close();
    input.close();
    // System.out.println(DB_NAME + "Database Copied !");
}

@Override
public void onCreate(SQLiteDatabase db) {

}

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

}

public void openDataBase() throws SQLException {
    // Open the database
    String myPath = DB_PATH + DB_NAME;
    db = SQLiteDatabase.openDatabase(myPath, null,
            SQLiteDatabase.OPEN_READWRITE);
}

public boolean isOpen() {
    if (db != null)
        return db.isOpen();
    return false;
}

@Override
public synchronized void close() {
    if (db != null)
        db.close();
    super.close();
}

private boolean checkDataBase() {
    SQLiteDatabase checkDB = null;
    try {
        String myPath = DB_PATH + DB_NAME;
        // System.out.println("My Pathe is:- " + myPath);
        // System.out.println("Open");
        checkDB = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);
        // System.out.println("checkDB value:" + checkDB);
        // System.out.println("My Pathe is:- " + myPath);
    } catch (Exception e) {
        // database does't exist yet.
    }

    if (checkDB != null) {
        // System.out.println("Closed");
        checkDB.close();
        // System.out.println("My db is:- " + checkDB.isOpen());
    }

    return checkDB != null ? true : false;
}

public Cursor execCursorQuery(String sql) {
    Cursor cursor = null;
    try {
        cursor = db.rawQuery(sql, null);
        GetCursor = cursor.getCount();
        Log.i("Inside execCursorQuery try", sql);
    } catch (Exception e) {
        Log.i("Inside execCursorQuery exception", e.getMessage());
    }
    return cursor;
}

public void execNonQuery(String sql) {
    try {
        db.execSQL(sql);
        // Log.d("SQL", sql);
    } catch (Exception e) {
        // Log.e("Err", e.getMessage());
    } finally {
        // closeDb();
    }
 }

在您的活动中，您应该通过以下方式调用它：

public class MainActivity extends Activity {
  DBConnect db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.layout);
    db= new DBConnect(MainActivity.this,"databasename");
  }

}

【讨论】：

  • 您好，感谢您的回复。但是代码还是不行。
  • 所以 while 循环现在也没有执行？
  • 为什么要在 oncreate() 方法上复制数据库？您只想复制它或从数据库中获取数据？
  • 我想在我的应用程序中使用数据库。由于无法直接从 assets 文件夹中使用现有数据库，因此必须创建数据库的本地副本。我稍后会根据需要使用复制的数据库来获取一些数据。
【解决方案3】：

使用此代码从资产文件夹复制数据库

    public class DataBaseHelper extends SQLiteOpenHelper 
{ 
private static String TAG = "DataBaseHelper"; // Tag just for the LogCat window 
//destination path (location) of our database on device 
private static String DB_PATH = "";  
//private static String DB_NAME ="(students).sqlite";// Database name 
private static String DB_NAME ="virtualDB";
private SQLiteDatabase mDataBase;  
private final Context mContext; 

public DataBaseHelper(Context context)  
{ 
    super(context, DB_NAME, null, 1);// 1? its Database Version 
    DB_PATH = "/data/data/" + context.getPackageName() + "/databases/"; 
    Log.i(TAG, DB_PATH);
    this.mContext = context; 
}    

public void createDataBase() 
{ 
    //If database not exists copy it from the assets 

    boolean mDataBaseExist = checkDataBase(); 
    if(!mDataBaseExist) 
    { 
        this.getReadableDatabase(); 
        this.close(); 
        try  
        { 
            //Copy the database from assests 
            copyDataBase(); 
            Log.e(TAG, "createDatabase database created"); 
        }  
        catch (IOException mIOException)  
        { 
             Log.i(TAG, "createDataBase "+mIOException+"");
        } 
    } 
} 
    //Check that the database exists here: /data/data/your package/databases/Da Name 
    private boolean checkDataBase() 
    { 
        File dbFile = new File(DB_PATH + DB_NAME); 
        //Log.v("dbFile", dbFile + "   "+ dbFile.exists()); 
        return dbFile.exists(); 
    } 

    //Copy the database from assets 
    private void copyDataBase() throws IOException 
    {  try  
    { 
        InputStream mInput = mContext.getAssets().open(DB_NAME); 
        String outFileName = DB_PATH + DB_NAME; 
        OutputStream mOutput = new FileOutputStream(outFileName); 
        byte[] mBuffer = new byte[1024]; 
        int mLength; 
        while ((mLength = mInput.read(mBuffer))>0) 
        { 
            mOutput.write(mBuffer, 0, mLength); 
        } 
        mOutput.flush(); 
        mOutput.close(); 
        mInput.close(); 
    }  
    catch (IOException mIOException)  
    { Log.i(TAG,"copyDataBase "+ mIOException+"");

    } 
    } 

    //Open the database, so we can query it 
    public boolean openDataBase() throws SQLException 
    { 
        String mPath = DB_PATH + DB_NAME; 
        //Log.v("mPath", mPath); 
        mDataBase = SQLiteDatabase.openDatabase(mPath, null, SQLiteDatabase.CREATE_IF_NECESSARY); 
        //mDataBase = SQLiteDatabase.openDatabase(mPath, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS); 
        return mDataBase != null; 
    } 

    @Override 
    public synchronized void close()  
    { 
        if(mDataBase != null) 
            mDataBase.close(); 
        super.close(); 
    }

    @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

    } 

}

这段代码对我来说很好，希望对你有帮助

【讨论】：

    【解决方案4】：

    请查看此支持项目以处理资产中的 sqlite db https://github.com/jgilfelt/android-sqlite-asset-helper，希望对您有所帮助。

    【讨论】：

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