[Android]关于android sqlite database存储到sdcard上的问题
最近碰到apk和后台的cpp code都需要访问一个数据库的问题。结果发现apk中创建的数据库外部的进程是没有权限去读/写的。这就需要把数据库文件创建到sdcard上。
后来发现在SQLiteOpenHelper(frameworks/base/core/java/android/database/sqlite/SQLiteOpenHelper.java)这个类中，创建数据库文件的路径是使用传入的contex的getDatabasePath获取的，这个是不允许修改的（至少我没有找到）。
那我就仿照这个SQLiteOpenHelper写了一个abstract class SDSQLiteOpenHelper，其使用和SQLiteOpenHelper一样，然后只要加上相应的permission，这样就可以实现把数据库存储到sdcard上了。
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 SDSQLiteOpenHelper {
??? private static final String TAG = SDSQLiteOpenHelper.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 SDSQLiteOpenHelper(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;
??????? }
??? }
?? ?
??? public File getDatabasePath(String name)
??? {
??????????? return new File("/sdcard/" + name);
??? }
??? /**
???? * 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) {}
}
