Split java.util.stream.Stream

Question

I have a text file that contains URLs and emails. I need to extract all of them from the file. Each URL and email can be found more then once, but result shouldn't contain duplicates. I can extract all URLs using the following code:

Files.lines(filePath).
    .map(urlPattern::matcher)
    .filter(Matcher::find)
    .map(Matcher::group)
    .distinct();

I can extract all emails using the following code:

Files.lines(filePath).
    .map(emailPattern::matcher)
    .filter(Matcher::find)
    .map(Matcher::group)
    .distinct();

Can I extract all URLs and emails reading the stream returned by Files.lines(filePath) only one time? Something like splitting stream of lines to stream of URLs and stream of emails.

Answer 1

You can use partitioningBy collector, though it's still not very elegant solution.

Map<Boolean, List<String>> map = Files.lines(filePath)
        .filter(str -> urlPattern.matcher(str).matches() ||
                       emailPattern.matcher(str).matches())
        .distinct()
        .collect(Collectors.partitioningBy(str -> urlPattern.matcher(str).matches()));
List<String> urls = map.get(true);
List<String> emails = map.get(false);

If you don't want to apply regexp twice, you can make it using the intermediate pair object (for example, SimpleEntry):

public static String classify(String str) {
    return urlPattern.matcher(str).matches() ? "url" : 
        emailPattern.matcher(str).matches() ? "email" : null;
}

Map<String, Set<String>> map = Files.lines(filePath)
        .map(str -> new AbstractMap.SimpleEntry<>(classify(str), str))
        .filter(e -> e.getKey() != null)
        .collect(Collectors.groupingBy(e -> e.getKey(),
            Collectors.mapping(e -> e.getValue(), Collectors.toSet())));

Using my free StreamEx library the last step would be shorter:

Map<String, Set<String>> map = StreamEx.of(Files.lines(filePath))
        .mapToEntry(str -> classify(str), Function.identity())
        .nonNullKeys()
        .grouping(Collectors.toSet());

Answer 2

You can perform the matching within a Collector:

Map<String,Set<String>> map=Files.lines(filePath)
    .collect(HashMap::new,
        (hm,line)-> {
            Matcher m=emailPattern.matcher(line);
            if(m.matches())
              hm.computeIfAbsent("mail", x->new HashSet<>()).add(line);
            else if(m.usePattern(urlPattern).matches())
              hm.computeIfAbsent("url", x->new HashSet<>()).add(line);
        },
        (m1,m2)-> m2.forEach((k,v)->m1.merge(k, v,
                                     (s1,s2)->{s1.addAll(s2); return s1;}))
    );
Set<String> mail=map.get("mail"), url=map.get("url");

Note that this can easily be adapted to find multiple matches within a line:

Map<String,Set<String>> map=Files.lines(filePath)
    .collect(HashMap::new,
        (hm,line)-> {
            Matcher m=emailPattern.matcher(line);
            while(m.find())
              hm.computeIfAbsent("mail", x->new HashSet<>()).add(m.group());
            m.usePattern(urlPattern).reset();
            while(m.find())
              hm.computeIfAbsent("url", x->new HashSet<>()).add(m.group());
        },
        (m1,m2)-> m2.forEach((k,v)->m1.merge(k, v,
                                     (s1,s2)->{s1.addAll(s2); return s1;}))
    );