如何在Android应用程序中使用现有的数据库

我已经创build了一个SQLite数据库。 我想用我的Android项目使用这个数据库文件。 我想将这个数据库与我的应用程序绑定。

应用程序如何访问这个数据库并将其用作其数据库，而不是创build一个新的数据库？

Answer 1

注意：在尝试此代码之前，请在以下代码中find此行：

 private static String DB_NAME ="YourDbName"; // Database name 

DB_NAME这里是你的数据库的名字。 假设您在资产文件夹中有一个数据库副本，例如，如果您的数据库名称是ordersDB，那么DB_NAME的值将是ordersDB，

 private static String DB_NAME ="ordersDB"; 

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将数据库保存在资产文件夹中 ，然后按照以下步骤操作

DataHelper类：

 import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import android.content.Context; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log; 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 ="YourDbName";// Database name private SQLiteDatabase mDataBase; private final Context mContext; public DataBaseHelper(Context context) { super(context, DB_NAME, null, 1);// 1? Its database Version if(android.os.Build.VERSION.SDK_INT >= 17){ DB_PATH = context.getApplicationInfo().dataDir + "/databases/"; } else { DB_PATH = "/data/data/" + context.getPackageName() + "/databases/"; } this.mContext = context; } public void createDataBase() throws IOException { //If the database does not exist, 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) { throw new Error("ErrorCopyingDataBase"); } } } //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 { 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(); } //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(); } } 

编写一个DataAdapter类，如下所示：

 import java.io.IOException; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.util.Log; public class TestAdapter { protected static final String TAG = "DataAdapter"; private final Context mContext; private SQLiteDatabase mDb; private DataBaseHelper mDbHelper; public TestAdapter(Context context) { this.mContext = context; mDbHelper = new DataBaseHelper(mContext); } public TestAdapter createDatabase() throws SQLException { try { mDbHelper.createDataBase(); } catch (IOException mIOException) { Log.e(TAG, mIOException.toString() + " UnableToCreateDatabase"); throw new Error("UnableToCreateDatabase"); } return this; } public TestAdapter open() throws SQLException { try { mDbHelper.openDataBase(); mDbHelper.close(); mDb = mDbHelper.getReadableDatabase(); } catch (SQLException mSQLException) { Log.e(TAG, "open >>"+ mSQLException.toString()); throw mSQLException; } return this; } public void close() { mDbHelper.close(); } public Cursor getTestData() { try { String sql ="SELECT * FROM myTable"; Cursor mCur = mDb.rawQuery(sql, null); if (mCur!=null) { mCur.moveToNext(); } return mCur; } catch (SQLException mSQLException) { Log.e(TAG, "getTestData >>"+ mSQLException.toString()); throw mSQLException; } } } 

现在你可以像这样使用它：

 TestAdapter mDbHelper = new TestAdapter(urContext); mDbHelper.createDatabase(); mDbHelper.open(); Cursor testdata = mDbHelper.getTestData(); mDbHelper.close(); 

编辑：感谢JDx

对于Android 4.1 （Jelly Bean），更改：

 DB_PATH = "/data/data/" + context.getPackageName() + "/databases/"; 

至：

 DB_PATH = context.getApplicationInfo().dataDir + "/databases/"; 

在DataHelper类中，这个代码将在JB 4.2多用户上工作。

Answer 2

尝试在Android应用程序中使用自己的SQLite数据库 。

Answer 3

如果您已经预build了数据库，而不是将其复制到资产文件夹中，并创build一个新类作为实现SQLiteOpenHelper的 DataBaseHelper而不是使用以下代码：

 import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; public class DataBaseHelperClass extends SQLiteOpenHelper{ //The Android's default system path of your application database. private static String DB_PATH = "/data/data/package_name/databases/"; // Data Base Name. private static final String DATABASE_NAME = "DBName.sqlite"; // Data Base Version. private static final int DATABASE_VERSION = 1; // Table Names of Data Base. static final String TABLE_Name = "tableName"; public Context context; static SQLiteDatabase sqliteDataBase; /** * Constructor * Takes and keeps a reference of the passed context in order to access to the application assets and resources. * @param context * Parameters of super() are 1. Context * 2. Data Base Name. * 3. Cursor Factory. * 4. Data Base Version. */ public DataBaseHelperClass(Context context) { super(context, DATABASE_NAME, null ,DATABASE_VERSION); this.context = context; } /** * Creates a empty database on the system and rewrites it with your own database. * 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. * */ public void createDataBase() throws IOException{ //check if the database exists boolean databaseExist = checkDataBase(); if(databaseExist){ // Do Nothing. }else{ this.getWritableDatabase(); copyDataBase(); }// end if else dbExist } // end createDataBase(). /** * 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 */ public boolean checkDataBase(){ File databaseFile = new File(DB_PATH + DATABASE_NAME); return databaseFile.exists(); } /** * 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 transferring byte stream. * */ private void copyDataBase() throws IOException{ //Open your local db as the input stream InputStream myInput = context.getAssets().open(DATABASE_NAME); // Path to the just created empty db String outFileName = DB_PATH + DATABASE_NAME; //Open the empty db as the output stream OutputStream myOutput = new FileOutputStream(outFileName); //transfer bytes from the input file to the output file 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(); } /** * This method opens the data base connection. * First it create the path up till data base of the device. * Then create connection with data base. */ public void openDataBase() throws SQLException{ //Open the database String myPath = DB_PATH + DATABASE_NAME; sqliteDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE); } /** * This Method is used to close the data base connection. */ @Override public synchronized void close() { if(sqliteDataBase != null) sqliteDataBase.close(); super.close(); } /** * Apply your methods and class to fetch data using raw or queries on data base using * following demo example code as: */ public String getUserNameFromDB(){ String query = "select User_First_Name From "+TABLE_USER_DETAILS; Cursor cursor = sqliteDataBase.rawQuery(query, null); String userName = null; if(cursor.getCount()>0){ if(cursor.moveToFirst()){ do{ userName = cursor.getString(0); }while (cursor.moveToNext()); } } return userName; } @Override public void onCreate(SQLiteDatabase db) { // No need to write the create table query. // As we are using Pre built data base. // Which is ReadOnly. } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // No need to write the update table query. // As we are using Pre built data base. // Which is ReadOnly. // We should not update it as requirements of application. } } 

希望这会帮助你…

Answer 4

我对其他DatabaseHelpers有关这个问题的麻烦，不知道为什么。
这对我来说是有效的：

 import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log; public class DatabaseHelper extends SQLiteOpenHelper { private static final String TAG = DatabaseHelper.class.getSimpleName(); private final Context context; private final String assetPath; private final String dbPath; public DatabaseHelper(Context context, String dbName, String assetPath) throws IOException { super(context, dbName, null, 1); this.context = context; this.assetPath = assetPath; this.dbPath = "/data/data/" + context.getApplicationContext().getPackageName() + "/databases/" + dbName; checkExists(); } /** * Checks if the database asset needs to be copied and if so copies it to the * default location. * * @throws IOException */ private void checkExists() throws IOException { Log.i(TAG, "checkExists()"); File dbFile = new File(dbPath); if (!dbFile.exists()) { Log.i(TAG, "creating database.."); dbFile.getParentFile().mkdirs(); copyStream(context.getAssets().open(assetPath), new FileOutputStream( dbFile)); Log.i(TAG, assetPath + " has been copied to " + dbFile.getAbsolutePath()); } } private void copyStream(InputStream is, OutputStream os) throws IOException { byte buf[] = new byte[1024]; int c = 0; while (true) { c = is.read(buf); if (c == -1) break; os.write(buf, 0, c); } is.close(); os.close(); } @Override public void onCreate(SQLiteDatabase db) { } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { } } 

Answer 5

如果您已有数据库，请将其保存在您的资产文件夹中，并将其复制到您的应用程序中。 有关更多详细信息，请参阅Android数据库基础 。

Answer 6

您可以通过使用内容提供者来完成此操作。 应用程序中使用的每个数据项对于应用程序都是私有的。 如果应用程序想要跨应用程序共享数据，则只能通过使用提供访问该私有数据的接口的内容提供者来实现此目的。