refactoring legacy code for java 8

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refactoring legacy code for java 8

June 25th, 2016 by Jeanne Boyarsky

I asked a teammate at CodeRanch if I could use a method he wrote to show how it could be written more clearly/succinctly in Java 8. He said yes. This is the original method. It is 95 lines and has a cyclomatic complexity of 27.

public static Map<Category, List<Forum>> getBetaTopForums(BestTopicsDAO bestTopicDAO, int userId, List<Topic> bestThisYear, List<Topic> secondaryBestList){
        Map<Integer, Integer> ratings = bestTopicDAO.selectForumRatingsByUserId(userId);
        
        List<Integer> forumIds = new ArrayList<>();
        List<Integer> ratedForumIds = CollectionCommon.getKeysSortedByValues(ratings, true);
        final int defaultUserId = SystemGlobals.getIntValue(ConfigKeys.BEST_TOPICS_DEFAULT_USER_ID);
        
        // Let's first add the forums that are rated above 5/10
        for(Integer forumId: ratedForumIds){
            Integer r = ratings.get(forumId);
            if(r != null && r > 5){
                forumIds.add(forumId);
            }
        }
        
        // Now let's add the forums found in best topics.
        if(bestThisYear != null){
            for(Topic topic: bestThisYear){
                int forumId = topic.getForumId();
                if(!forumIds.contains(forumId)){
                    forumIds.add(forumId);
                }
            }
        }
        if(secondaryBestList != null){
            for(Topic topic: secondaryBestList){
                int forumId = topic.getForumId();
                if(!forumIds.contains(forumId)){
                    forumIds.add(forumId);
                }
            }
        }
        
        // If this user is not the default-rating-user, let's add the top forums
        // rated by the default-rating-user.
        if(userId != defaultUserId) {
            Collection<Integer> fids = getTopRatedForumIds(bestTopicDAO);
            for(Integer fid: fids) {
                if(fid != null && !forumIds.contains(fid)) {
                    forumIds.add(fid);
                }
            }
        }
        
        
        // Let's also add some forums found in hot topics.
        List<Topic> tmpTopics = TopicRepository.getHottestTopics();
        for(Topic topic: tmpTopics){
            int forumId = topic.getForumId();
            if(!forumIds.contains(forumId)){
                forumIds.add(forumId);
            }
        }
        
        // Finally, let's add the forums that were rated below 6/10
        for(Integer forumId: ratedForumIds){
            Integer r = ratings.get(forumId);
            if(r != null && r < 6 && !forumIds.contains(forumId)){
                forumIds.add(forumId);
            }
        }
        
        Map<Category, List<Forum>> forums = new LinkedHashMap<>();
        
        PermissionControl pc = SecurityRepository.get(userId);
        
        final int maxTopForums = SystemGlobals.getIntValue(ConfigKeys.BETA_VIEW_MAX_TOP_FORUMS_IN_HOME);
        int forumsToShow = 0;
        
        // We need to remove the forums that are not visible, or rated 0/10
        for(Integer forumId: forumIds){
            if(pc.canAccess(SecurityConstants.PERM_FORUM, String.valueOf(forumId))){
                Forum f = ForumRepository.getForum(forumId);
                Category c = f != null ? ForumRepository.getCategory(f.getCategoryId()) : null;
                if(f != null && c != null && f.isShowInForumList()){
                    
                    if(++forumsToShow > maxTopForums){
                        break;
                    }
                    
                    List<Forum> fs;
                    if(forums.containsKey(c)){
                        fs = forums.get(c);
                    }else{
                        fs = new ArrayList<>();
                        forums.put(c, fs);
                    }
                    fs.add(f);
                }
            }
        }
        return forums;
        
    }

First step – write unit tests

First, I wrote unit tests for the existing code to ensure I didn’t break anything. While doing that, I did some minor refactorings. (I didn’t do extract method to make the method shorter since I knew I’d be updating that later). What I did change:

  1. Removed BestTopicsDAO as a parameter. It comes from a factory and we have a mock framework setup for that factory already. So there was no reason it had to be a parameter
  2. Renamed bestThisYear to primaryBestList. (It doesn’t always represent the best for the year)

I couldn’t get 100% test coverage because a few of the null checks were unreachable due to early logic (in the helper methods.) I left them in to see the effect they’d have on conversion.

Refactoring to Java 8 – Getting started

There’s a lot of for loops here. And I suspect they are very similar. Let’s start with the first one:

for(Integer forumId: ratedForumIds){
  Integer r = ratings.get(forumId);
  if(r != null && r > 5){
    forumIds.add(forumId);
  }
}

I converted this to a helper method and a stream:

forumIds.addAll(ratedForumIds.stream().filter(id -> {
  Integer r = ratings.get(id);
  return r != null && r > 5;
}).collect(Collectors.toList()));

I’ll grant you that this code isn’t shorter than the original code. It is more similar in form to the code I expect to write next though.  Also, it’s not easier to read given I didn’t extract the two line lambda. I’m going to do that after I get rid of the similar for loops.

The next refactoring

The next one is interesting. It’s just a for loop and if statement which is easy to rewrite.

for(Topic topic: primaryBestList){
  int forumId = topic.getForumId();
  if(!forumIds.contains(forumId)){
    forumIds.add(forumId);
  }
}

which is equivalent to

forumIds.addAll(primaryBestList.stream()
  .map(Topic::getForumId)
  .filter(f -> ! forumIds.contains(f))
  .collect(Collectors.toList()));

However, it is interesting because it check if the forum is already in forumIds. This shouldn’t be necessary as it is something a data structure could do. We need a data structure that is both a list (preserves order) and a set (checks for uniqueness.) Enter LinkedHashSet. It’s a set and preserves the insertion order. The JavaDoc even specifies that if you add the same element again, the order doesn’t change. Perfect. Switching forumIds to a LinkedHashSet allows for getting rid of the filter intermediate operation. And the unit tests still work.  I used the same techniques for the next five for loops.

Time to use methods

I converted two methods that had to do with ratings and three that were straight conversions.  I could have one common method they all use with identities for the filter/map that don’t apply. Two methods would be clearer. Giving me:

private static void addForumIds(Collection<Integer> forumIds, List<Topic> candidates) {
  if (candidates != null) {
    List<Integer> toAdd = candidates.stream().map(Topic::getForumId).collect(Collectors.toList());
    forumIds.addAll(toAdd);
  }
}

private static void addForumIds(Collection<Integer> forumIds, Collection<Integer> candidates, Predicate<Integer> predicate) {
  if (candidates != null) {
    List<Integer> toAdd = candidates.stream().filter(predicate).collect(Collectors.toList());
    forumIds.addAll(toAdd);
  }
}

The last one

The last chunk of code needed more refactoring to take care of all the forum filtering logic first. It also needed a mutable object for the counter rather than a primitive so it could be updated inside a lambda.

Conclusion

I could refactor this more. There’s duplication in the two lambdas. And I could extract more code into separate methods. Interestingly, the total code base is about the same as before. (It’s actually three lines longer, but I have more than three lines of comments.) But the method with the main logic is shorter and far less complicated:

public static Map<Category, List<Forum>> getBetaTopForums(int userId, List<Topic> primaryBestList, List<Topic> secondaryBestList){
        BestTopicsDAO bestTopicDAO = DataAccessDriver.newBestTopicDAO();
        Map<Integer, Integer> ratings = bestTopicDAO.selectForumRatingsByUserId(userId);
        
        Collection<Integer> forumIds = new LinkedHashSet<>();
        List<Integer> ratedForumIds = CollectionCommon.getKeysSortedByValues(ratings, true);
        final int defaultUserId = SystemGlobals.getIntValue(ConfigKeys.BEST_TOPICS_DEFAULT_USER_ID);
        
        // Let's first add the forums that are rated above 5/10
         addForumIds(forumIds, ratedForumIds, id -> {
            Integer r = ratings.get(id);
            return r != null && r > 5;
        });
        
        // Now let's add the forums found in best topics.
        addForumIds(forumIds, primaryBestList);
        addForumIds(forumIds, secondaryBestList);
          
        // If this user is not the default-rating-user, let's add the top forums
        // rated by the default-rating-user.
        if(userId != defaultUserId) {
            Collection<Integer> fids = getTopRatedForumIds(bestTopicDAO);
            addForumIds(forumIds, fids, id -> id != null);
        }
        
        // Let's also add some forums found in hot topics.
        List<Topic> tmpTopics = TopicRepository.getHottestTopics();
        addForumIds(forumIds, tmpTopics);

        // Finally, let's add the forums that were rated below 6/10
       addForumIds(forumIds, ratedForumIds, id -> {
            Integer r = ratings.get(id);
            return r != null && r < 6;
        });
        
        Map<Category, List<Forum>> forums = new LinkedHashMap<>();
        
        PermissionControl pc = SecurityRepository.get(userId);
        
        final int maxTopForums = SystemGlobals.getIntValue(ConfigKeys.BETA_VIEW_MAX_TOP_FORUMS_IN_HOME);
        AtomicInteger countForumsToShow = new AtomicInteger(0);
        
        // We need to remove the forums that are not visible, or rated 0/10
        forumIds.stream()
             // skip if can't access forum
            .filter(id -> pc.canAccess(SecurityConstants.PERM_FORUM, String.valueOf(id)))
            // get forum
            .map(ForumRepository::getForum)
            // skip if forum not found or can't access
            .filter(f -> f != null && f.isShowInForumList())
            // get category
            .forEach(f -> addForumToCategory(forums, f, maxTopForums, countForumsToShow));
        
        return forums;
        
    }
    
    private static void addForumToCategory(Map<Category, List<Forum>> forums, Forum f, int maxTopForums,
            AtomicInteger countForumsToShow) {
        Category c = ForumRepository.getCategory(f.getCategoryId());
        if (c != null && countForumsToShow.incrementAndGet() <= maxTopForums) {
            List<Forum> fs;
            if (forums.containsKey(c)) {
                fs = forums.get(c);
            } else {
                fs = new ArrayList<>();
                forums.put(c, fs);
            }
            fs.add(f);
        }
    }

    private static void addForumIds(Collection<Integer> forumIds, List<Topic> candidates) {
        if (candidates != null) {
            List<Integer> toAdd = candidates.stream().map(Topic::getForumId).collect(Collectors.toList());
            forumIds.addAll(toAdd);
        }
    }
    
    private static void addForumIds(Collection<Integer> forumIds, Collection<Integer> candidates, Predicate<Integer> predicate) {
        if (candidates != null) {
            List<Integer> toAdd = candidates.stream().filter(predicate).collect(Collectors.toList());
            forumIds.addAll(toAdd);
        }    
    }

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