基于Android如何实现将数据库保存到SD卡

/**  * Create and/or open a database that will be used for reading and writing.  * The first time this is called, the database will be opened and  * {@link #onCreate}, {@link #onUpgrade} and/or {@link #onOpen} will be  * called.  *  * <p>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 the database.)  * Errors such as bad permissions or a full disk may cause this method  * to fail, but future attempts may succeed if the problem is fixed.</p>  *  * <p class="caution">Database upgrade may take a long time, you  * should not call this method from the application main thread, including  * from {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}.  *  * @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) {   if (!mDatabase.isOpen()) {    // darn! the user closed the database by calling mDatabase.close()    mDatabase = null;   } else if (!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;  if (mDatabase != null) mDatabase.lock();  try {   mIsInitializing = true;   if (mName == null) {    db = SQLiteDatabase.create(null);   } else {    db = mContext.openOrCreateDatabase(mName, 0, mFactory, mErrorHandler);   }   int version = db.getVersion();   if (version != mNewVersion) {    db.beginTransaction();    try {     if (version == 0) {      onCreate(db);     } else {      if (version > mNewVersion) {       onDowngrade(db, version, mNewVersion);      } 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.unlock();    }    mDatabase = db;   } else {    if (mDatabase != null) mDatabase.unlock();    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.  *  * <p class="caution">Like {@link #getWritableDatabase}, this method may  * take a long time to return, so you should not call it from the  * application main thread, including from  * {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}.  *  * @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) {   if (!mDatabase.isOpen()) {    // darn! the user closed the database by calling mDatabase.close()    mDatabase = null;   } else {    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 = mContext.getDatabasePath(mName).getPath();   db = SQLiteDatabase.openDatabase(path, mFactory, SQLiteDatabase.OPEN_READONLY,     mErrorHandler);   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();  } }

public class DatabaseContext extends ContextWrapper { public DatabaseContext(Context context){  super( context ); } /**  * 获得数据库路径，如果不存在，则创建对象对象  * @param name  * @param mode  * @param factory  */ @Override public File getDatabasePath(String name) {  //判断是否存在sd卡  boolean sdExist = android.os.Environment.MEDIA_MOUNTED.equals(android.os.Environment.getExternalStorageState());  if(!sdExist){//如果不存在,   return null;  }else{//如果存在   //获取sd卡路径   String dbDir= FileUtils.getFlashBPath();   dbDir += "DB";//数据库所在目录   String dbPath = dbDir+"/"+name;//数据库路径   //判断目录是否存在，不存在则创建该目录   File dirFile = new File(dbDir);   if(!dirFile.exists()){    dirFile.mkdirs();   }   //数据库文件是否创建成功   boolean isFileCreateSuccess = false;    //判断文件是否存在，不存在则创建该文件   File dbFile = new File(dbPath);   if(!dbFile.exists()){    try {        isFileCreateSuccess = dbFile.createNewFile();//创建文件    } catch (IOException e) {     e.printStackTrace();    }   }else{    isFileCreateSuccess = true;   }   //返回数据库文件对象   if(isFileCreateSuccess){    return dbFile;   }else{    return null;   }  } } /**  * 重载这个方法，是用来打开SD卡上的数据库的，android 2.3及以下会调用这个方法。  *   * @param name  * @param mode  * @param factory  */ @Override public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory) {  SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), null);  return result; } /**  * Android 4.0会调用此方法获取数据库。  *   * @see android.content.ContextWrapper#openOrCreateDatabase(java.lang.String, int,   *   android.database.sqlite.SQLiteDatabase.CursorFactory,  *   android.database.DatabaseErrorHandler)  * @param name  * @param mode  * @param factory  * @param errorHandler  */ @Override public SQLiteDatabase openOrCreateDatabase(String name, int mode, CursorFactory factory, DatabaseErrorHandler errorHandler) {  SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), null);  return result; }}

DatabaseContext dbContext = new DatabaseContext(context);super(dbContext, mDatabaseName, null, VERSION);