自定义抽象类CustomSQLiteOpenHelper,实现SQLiteDB自由存储(eg. SDCARD)

自已写一个抽象类 CustomSQLiteOpenHelper，对SQLiteOpenHelper稍加修改，这样就可以实现把数据库存储到sdcard上了。访问的时候就可以直接从sdcard进行访问。

import java.io.File;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteException;import android.database.sqlite.SQLiteDatabase.CursorFactory;import android.util.Log;/*** A helper class to manage database creation and version management.* You create a subclass implementing {@link #onCreate}, {@link #onUpgrade} and* optionally {@link #onOpen}, and this class takes care of opening the database* if it exists, creating it if it does not, and upgrading it as necessary.* Transactions are used to make sure the database is always in a sensible state.* <p>For an example, see the NotePadProvider class in the NotePad sample application,* in the <em>samples/</em> directory of the SDK.</p>*/public abstract class CustomSQLiteOpenHelper {    private static final String TAG = CustomSQLiteOpenHelper.class.getSimpleName();    private final Context mContext;    private final String mName;    private final CursorFactory mFactory;    private final int mNewVersion;    private SQLiteDatabase mDatabase = null;    private boolean mIsInitializing = false;    /**     * Create a helper object to create, open, and/or manage a database.     * The database is not actually created or opened until one of     * {@link #getWritableDatabase} or {@link #getReadableDatabase} is called.     *     * @param context to use to open or create the database     * @param name of the database file, or null for an in-memory database     * @param factory to use for creating cursor objects, or null for the default     * @param version number of the database (starting at 1); if the database is older,     *     {@link #onUpgrade} will be used to upgrade the database     */    public CustomSQLiteOpenHelper(Context context, String name, CursorFactory factory, int version) {        if (version < 1) throw new IllegalArgumentException("Version must be >= 1, was " + version);        mContext = context;        mName = name;        mFactory = factory;        mNewVersion = version;    }    /**     * Create and/or open a database that will be used for reading and writing.     * Once opened successfully, the database is cached, so you can call this     * method every time you need to write to the database.  Make sure to call     * {@link #close} when you no longer need it.     *     * <p>Errors such as bad permissions or a full disk may cause this operation     * to fail, but future attempts may succeed if the problem is fixed.</p>     *     * @throws SQLiteException if the database cannot be opened for writing     * @return a read/write database object valid until {@link #close} is called     */    public synchronized SQLiteDatabase getWritableDatabase() {        if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {            return mDatabase;  // The database is already open for business        }        if (mIsInitializing) {            throw new IllegalStateException("getWritableDatabase called recursively");        }        // If we have a read-only database open, someone could be using it        // (though they shouldn't), which would cause a lock to be held on        // the file, and our attempts to open the database read-write would        // fail waiting for the file lock.  To prevent that, we acquire the        // lock on the read-only database, which shuts out other users.        boolean success = false;        SQLiteDatabase db = null;        try {            mIsInitializing = true;            if (mName == null) {                db = SQLiteDatabase.create(null);            } else {                  String path = getDatabasePath(mName).getPath();                db = SQLiteDatabase.openOrCreateDatabase(path, mFactory);                   }            int version = db.getVersion();            if (version != mNewVersion) {                db.beginTransaction();                try {                    if (version == 0) {                        onCreate(db);                    } else {                        onUpgrade(db, version, mNewVersion);                    }                    db.setVersion(mNewVersion);                    db.setTransactionSuccessful();                } finally {                    db.endTransaction();                }            }            onOpen(db);            success = true;            return db;        } finally {            mIsInitializing = false;            if (success) {                if (mDatabase != null) {                    try { mDatabase.close(); } catch (Exception e) { }                }                mDatabase = db;            } else {                if (db != null) db.close();            }        }    }    /**     * Create and/or open a database.  This will be the same object returned by     * {@link #getWritableDatabase} unless some problem, such as a full disk,     * requires the database to be opened read-only.  In that case, a read-only     * database object will be returned.  If the problem is fixed, a future call     * to {@link #getWritableDatabase} may succeed, in which case the read-only     * database object will be closed and the read/write object will be returned     * in the future.     *     * @throws SQLiteException if the database cannot be opened     * @return a database object valid until {@link #getWritableDatabase}     *     or {@link #close} is called.     */    public synchronized SQLiteDatabase getReadableDatabase() {        if (mDatabase != null && mDatabase.isOpen()) {            return mDatabase;  // The database is already open for business        }        if (mIsInitializing) {            throw new IllegalStateException("getReadableDatabase called recursively");        }        try {            return getWritableDatabase();        } catch (SQLiteException e) {            if (mName == null) throw e;  // Can't open a temp database read-only!            Log.e(TAG, "Couldn't open " + mName + " for writing (will try read-only):", e);        }        SQLiteDatabase db = null;        try {            mIsInitializing = true;            String path = getDatabasePath(mName).getPath();            db = SQLiteDatabase.openDatabase(path, mFactory, SQLiteDatabase.OPEN_READWRITE);            if (db.getVersion() != mNewVersion) {                throw new SQLiteException("Can't upgrade read-only database from version " +                        db.getVersion() + " to " + mNewVersion + ": " + path);            }            onOpen(db);            Log.w(TAG, "Opened " + mName + " in read-only mode");            mDatabase = db;            return mDatabase;        } finally {            mIsInitializing = false;            if (db != null && db != mDatabase) db.close();        }    }    /**     * Close any open database object.     */    public synchronized void close() {        if (mIsInitializing) throw new IllegalStateException("Closed during initialization");        if (mDatabase != null && mDatabase.isOpen()) {            mDatabase.close();            mDatabase = null;        }    }    /**     * Called when the database is created for the first time. This is where the     * creation of tables and the initial population of the tables should happen.     *     * @param db The database.     */    public abstract void onCreate(SQLiteDatabase db);    /**     * Called when the database needs to be upgraded. The implementation     * should use this method to drop tables, add tables, or do anything else it     * needs to upgrade to the new schema version.     *     * <p>The SQLite ALTER TABLE documentation can be found     * <a href="http://sqlite.org/lang_altertable.html">here</a>. If you add new columns     * you can use ALTER TABLE to insert them into a live table. If you rename or remove columns     * you can use ALTER TABLE to rename the old table, then create the new table and then     * populate the new table with the contents of the old table.     *     * @param db The database.     * @param oldVersion The old database version.     * @param newVersion The new database version.     */    public abstract void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion);    /**     * Called when the database has been opened.     * Override method should check {@link SQLiteDatabase#isReadOnly} before     * updating the database.     *     * @param db The database.     */    public void onOpen(SQLiteDatabase db) {}   /**     * 获取DB存储路径     */   public File getDatabasePath(String dbpath)     {            return new File(Environment.getExternalStorageDirectory()+"/" + dbpath);     }}