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      1 /*
      2  * Copyright (C) 2009 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.database.sqlite;
     18 
     19 import android.content.res.AssetFileDescriptor;
     20 import android.database.Cursor;
     21 import android.os.MemoryFile;
     22 
     23 import java.io.FileNotFoundException;
     24 import java.io.IOException;
     25 
     26 /**
     27  * Some helper functions for using SQLite database to implement content providers.
     28  *
     29  * @hide
     30  */
     31 public class SQLiteContentHelper {
     32 
     33     /**
     34      * Runs an SQLite query and returns an AssetFileDescriptor for the
     35      * blob in column 0 of the first row. If the first column does
     36      * not contain a blob, an unspecified exception is thrown.
     37      *
     38      * @param db Handle to a readable database.
     39      * @param sql SQL query, possibly with query arguments.
     40      * @param selectionArgs Query argument values, or {@code null} for no argument.
     41      * @return If no exception is thrown, a non-null AssetFileDescriptor is returned.
     42      * @throws FileNotFoundException If the query returns no results or the
     43      *         value of column 0 is NULL, or if there is an error creating the
     44      *         asset file descriptor.
     45      */
     46     public static AssetFileDescriptor getBlobColumnAsAssetFile(SQLiteDatabase db, String sql,
     47             String[] selectionArgs) throws FileNotFoundException {
     48         try {
     49             MemoryFile file = simpleQueryForBlobMemoryFile(db, sql, selectionArgs);
     50             if (file == null) {
     51                 throw new FileNotFoundException("No results.");
     52             }
     53             return AssetFileDescriptor.fromMemoryFile(file);
     54         } catch (IOException ex) {
     55             throw new FileNotFoundException(ex.toString());
     56         }
     57     }
     58 
     59     /**
     60      * Runs an SQLite query and returns a MemoryFile for the
     61      * blob in column 0 of the first row. If the first column does
     62      * not contain a blob, an unspecified exception is thrown.
     63      *
     64      * @return A memory file, or {@code null} if the query returns no results
     65      *         or the value column 0 is NULL.
     66      * @throws IOException If there is an error creating the memory file.
     67      */
     68     // TODO: make this native and use the SQLite blob API to reduce copying
     69     private static MemoryFile simpleQueryForBlobMemoryFile(SQLiteDatabase db, String sql,
     70             String[] selectionArgs) throws IOException {
     71         Cursor cursor = db.rawQuery(sql, selectionArgs);
     72         if (cursor == null) {
     73             return null;
     74         }
     75         try {
     76             if (!cursor.moveToFirst()) {
     77                 return null;
     78             }
     79             byte[] bytes = cursor.getBlob(0);
     80             if (bytes == null) {
     81                 return null;
     82             }
     83             MemoryFile file = new MemoryFile(null, bytes.length);
     84             file.writeBytes(bytes, 0, 0, bytes.length);
     85             file.deactivate();
     86             return file;
     87         } finally {
     88             cursor.close();
     89         }
     90     }
     91 
     92 }
     93