一个比较好的复制数据库的DBHelper类

public class DatabaseHelper extends SQLiteOpenHelper {
    private final String packageName = "应用的包名";
    private String DB_PATH = "/data/data/" + packageName + "/databases/";
    private SQLiteDatabase myDataBase;
    private final Context myContext;
    private static final String DB_NAME = "soft.db";
    private static String CITY = "city_name";
    public static final String CITY_ID = "city_id";
    public static final String CITY_NAME = "city_name";

    public DatabaseHelper(Context context) {
        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }

    /**
     * 创建空数据库，并且通过复制资源文件夹的数据库覆盖
     * */
    public void createDataBase() throws IOException {
        boolean dbExist = checkDataBase();
        if (dbExist) {// 存在，什么也不干

        } else {
            // 进行数据库的复制
            this.getReadableDatabase();
            try {
                copyDataBase();
            } catch (IOException e) {
                throw new Error("Error copying database");
            }
        }
    }

    /**
     * 查询操作
     *
     * @return
     */
    public Cursor getAllCity() {
        String col[] = new String[] { CITY_ID, CITY_NAME };
        // return db.rawQuery("select * from tb_diary",null);
        return myDataBase.query(CITY, col, null, null, null, null, null);
    }

    /**
     * 启动应用的时候去检查数据库是否存在，如果不存在，则需要调用copy数据库的方法
     *
     * @return 存在返回 true , 不存在返回false
     */
    boolean checkDataBase() {
        SQLiteDatabase checkDB = null;
        try {
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);
        } catch (SQLiteException e) {
            // 如果数据库不存在
            // throw new Error("Database does't exist yet.");
            return false;
        }
        if (checkDB != null) {
            checkDB.close();
        }
        return checkDB != null ? true : false;
    }

    /**
     *
     * 复制数据库的方法
     *
     * @throws IOException
     *
     * */
    void copyDataBase() throws IOException {
        // 通过资源文件访问数据库文件，以输入流的形式
        InputStream myInput = myContext.getAssets().open(DB_NAME);// 访问assets下的资源
        // InputStream
        // input=myContext.getResources().openRawResource(R.id.xx);//访问res下的资源
        // 数据库的 输出地址
        String outFileName = DB_PATH + DB_NAME;
        OutputStream myOutput = new FileOutputStream(outFileName);
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer)) > 0) {
            myOutput.write(buffer, 0, length);
            Log.i("data", "copying.....");
        }
        myOutput.flush();
        myOutput.close();
        myInput.close();

    }

    /**
     * 关闭数据库的方法
     */
    @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) {
    }

    /**
     * 打开数据库的方法
     *
     * @throws SQLException
     */
    public void openDataBase() throws SQLException {
        // Open the database
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READONLY);
    }
}