Utility class for loading migration files in Android assets directory

UpgradeHelper.java

/**
 * Used as a aid in the migration process for, loading required SQL files as specified by a given version
 * 
 * @author James Edward Morgan
 */
public class UpgradeHelper {

	private static final String LOG_TAG = "UpgradeHelper";

	protected static final Set<Integer> VERSION;
	static {
		VERSION = new LinkedHashSet<Integer>();
	}

	/**
	 * Add the given version to the list of available updates
	 */
	public static final void addUpgrade(final int version) {
		Logger.d(LOG_TAG, "Adding %s to upgrade path", version);
		VERSION.add(version);
	}

	/**
	 * Get all available SQL Statements
	 * 
	 * @param resources the {@link Resources} from the given {@link Context} which maybe using the helper class
	 * @return A list of SQL statements which have been included in the
	 */
	public static List<String> availableUpdates(final Resources resources) {
		final List<String> updates = new ArrayList<String>();

		for (final Integer version : VERSION) {
 		        // Migration files must be kept in assets/updates/migration-X.sql
			final String fileName = String.format("updates/migration-%s.sql", version);

			Logger.d(LOG_TAG, "Adding db version [%s] to update list, loading file [%s]", version, fileName);

			final String sqlStatements = loadAssetFile(resources, fileName);

			final String[] splitSql = sqlStatements.split("\\r?\\n");
			for (final String sql : splitSql) {
				if (isNotComment(sql)) {
					updates.add(sql);
				}
			}
		}
		return updates;
	}

	/**
	 * Load the given asset file, throws wrapped {@link RuntimeException} if not found
	 * 
	 * @param fileName of the file to load, including asset directory path and sub path if required
	 * @param resources the {@link Resources}, usually from a {@link Context}
	 * @return the fully loaded file as a {@link String}
	 */
	private static String loadAssetFile(final Resources resources, final String fileName) {
		try {
			final InputStream is = resources.getAssets().open(fileName);
			final byte[] buffer = new byte[is.available()];
			is.read(buffer);
			final ByteArrayOutputStream os = new ByteArrayOutputStream();
			os.write(buffer);
			os.close();
			is.close();
			return os.toString();
		}
		catch (final IOException e) {
			Logger.e(LOG_TAG, "IOException: ", e);
			throw new RuntimeException(e);
		}
	}

	/**
	 * A comment must consist of either '--' or '#'
	 * 
	 * @return true if not found to be an SQL Comment
	 */
	private static boolean isNotComment(final String sql) {
		return !StringUtils.startsWith(sql, "--") || !StringUtils.startsWith(sql, "#");
	}
}