void persistMovie(Movie movie) throws Exception {
String newValue = movieObjectWriter.writeValueAsString(movie);
String oldValue = movieMap.get(movie.getDbId());
if (!StringUtils.equals(newValue, oldValue)) {
// write movie to DB
movieMap.put(movie.getDbId(), newValue);
}
}
void removeMovieFromDb(Movie movie) throws Exception {
movieMap.remove(movie.getDbId());
}