Go语言视频零基础入门到精通

jspfan

        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。

java代码： 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.DatabopenOrCreatease(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);

}

}