Rewrite for loop as Java 8 Stream

Yamazaki 0
Viewed 63

I have the following java method which returns the ID of a single matched movie from a list of movies, the filter criteria is the movie's attributes, all attributes provided must match:

public Optional<String> getIdFromMatchedMovie(List<Movie> movies, Map<String, Object> attributes)
{
    Optional<Movie> movieOption = 
        movies.stream()
              .filter(movie -> {
                      for (Map.Entry<String, Object> attr : attributes.entrySet()) {

                           Object returnedAttrValue = movie.getAttributes()
                                                           .get(attr.getKey());

                           // Attribute provided not exists in movie's attributes
                           // or the attributes value don't match
                           if (returnedAttrValue == null
                               || !returnedAttrValue.equals(attr.getValue())) {
                                    return false;
                           }
                       }

                       return true;
               })
               .findFirst();

               if (movieOption.isPresent()) {
                   return movieOption.get().getId());
               }
               return Optional.empty();
}

Is there a way to rewrite this by remove the inner for loop and still leveraging the Java 8 Stream?

java-stream java
2 Answers

Sure, you can convert the filter loop to another nested stream. Also, the isPresent()-then-get() is often an anti-pattern when you're using optionals. In this case, you can use Optional.map() or even move it into the stream:

return movies.stream()
        .filter(movie -> attributes.entrySet()
                .stream()
                .allMatch(attr -> attr.getValue().equals(
                        movie.getAttributes().get(attr.getKey())))
        .map(Movie::getId)
        .findFirst();
shmosel0

You can replace the nested loop with a stream over the map entries and condition that checks the presence of the result and extracts id property with Optional.map():

public Optional<String> getIdFromMatchedMovie(List<Movie> movies,
                                              Map<String, Object> attributes) {
    return movies.stream()
        .filter(movie -> attributes.entrySet().stream()
            .allMatch(entry -> Objects.equals(
                movie.getAttributes().get(entry.getKey()),
                entry.getValue()
            ))
            .findFirst()
            .map(Movie::getId);
}
Alexander Ivanchenko0
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