Android example source code file (SQLiteContentHelper.java)

This example Android source code file (SQLiteContentHelper.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, assetfiledescriptor, content, cursor, database, filenotfoundexception, io, ioexception, memoryfile, os, sqlitecontenthelper, string

The SQLiteContentHelper.java Android example source code

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.database.sqlite;

import android.content.res.AssetFileDescriptor;
import android.database.Cursor;
import android.os.MemoryFile;

import java.io.FileNotFoundException;
import java.io.IOException;

/**
 * Some helper functions for using SQLite database to implement content providers.
 *
 * @hide
 */
public class SQLiteContentHelper {

    /**
     * Runs an SQLite query and returns an AssetFileDescriptor for the
     * blob in column 0 of the first row. If the first column does
     * not contain a blob, an unspecified exception is thrown.
     *
     * @param db Handle to a readable database.
     * @param sql SQL query, possibly with query arguments.
     * @param selectionArgs Query argument values, or {@code null} for no argument.
     * @return If no exception is thrown, a non-null AssetFileDescriptor is returned.
     * @throws FileNotFoundException If the query returns no results or the
     *         value of column 0 is NULL, or if there is an error creating the
     *         asset file descriptor.
     */
    public static AssetFileDescriptor getBlobColumnAsAssetFile(SQLiteDatabase db, String sql,
            String[] selectionArgs) throws FileNotFoundException {
        try {
            MemoryFile file = simpleQueryForBlobMemoryFile(db, sql, selectionArgs);
            if (file == null) {
                throw new FileNotFoundException("No results.");
            }
            return AssetFileDescriptor.fromMemoryFile(file);
        } catch (IOException ex) {
            throw new FileNotFoundException(ex.toString());
        }
    }

    /**
     * Runs an SQLite query and returns a MemoryFile for the
     * blob in column 0 of the first row. If the first column does
     * not contain a blob, an unspecified exception is thrown.
     *
     * @return A memory file, or {@code null} if the query returns no results
     *         or the value column 0 is NULL.
     * @throws IOException If there is an error creating the memory file.
     */
    // TODO: make this native and use the SQLite blob API to reduce copying
    private static MemoryFile simpleQueryForBlobMemoryFile(SQLiteDatabase db, String sql,
            String[] selectionArgs) throws IOException {
        Cursor cursor = db.rawQuery(sql, selectionArgs);
        if (cursor == null) {
            return null;
        }
        try {
            if (!cursor.moveToFirst()) {
                return null;
            }
            byte[] bytes = cursor.getBlob(0);
            if (bytes == null) {
                return null;
            }
            MemoryFile file = new MemoryFile(null, bytes.length);
            file.writeBytes(bytes, 0, 0, bytes.length);
            file.deactivate();
            return file;
        } finally {
            cursor.close();
        }
    }

}