如何在Android应用程序中使用现有数据库？

如何在Android应用程序中使用现有数据库？

注意： 在尝试此代码之前，请在以下代码中找到此行：

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

DB_NAME

此处是你的数据库的名称。假设你在

Assets

文件夹中有数据库的副本，因此，例如，如果你的数据库名称为

ordersDB

，则

DB_NAME

的值为

orderDB

，

private static String DB_NAME ="ordersDB";

将数据库保留在资产文件夹中，然后执行以下 *** 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    private static String DB_NAME ="YourDbName"; // Database name    private static int DB_VERSION = 1; // Database version    private final File DB_FILE;    private SQLiteDatabase mDatabase;    private final Context mContext;    public DatabaseHelper(Context context) {        super(context, DB_NAME, null, DB_VERSION);        DB_FILE = context.getDatabasePath(DB_NAME);        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 file exists in databases folder    private boolean checkDatabase() {        return DB_FILE.exists();    }    // Copy the database from assets    private void copyDatabase() throws IOException {        InputStream mInput = mContext.getAssets().open(DB_NAME);        OutputStream mOutput = new FileOutputStream(DB_FILE);        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 {        // Log.v("DB_PATH", DB_FILE.getAbsolutePath());        mDatabase = SQLiteDatabase.openDatabase(DB_FILE, null, SQLiteDatabase.CREATE_IF_NECESSARY);        // mDatabase = SQLiteDatabase.openDatabase(DB_FILE, 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，例如：

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();

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，此代码将在Jelly Bean 4.2多用户上运行。

编辑：代替使用硬编码路径，我们可以使用

DB_PATH = context.getDatabasePath(DB_NAME).getAbsolutePath();

这将为我们提供数据库文件的完整路径，并适用于所有Android版本