Creating map from list, where key is in part of inner and outer object

user_4743869 0
Viewed 103

Is it possible (in simple way) to change it into java8 Stream? (Please do not comment/answer if you want to tell me that two for are better and not all loops should be changed to streams, it's not a point)

final Map<String, String> map = new HashMap<>();

for(final Person person: list) {
    for(final Internal internal: person.getInternals()) {
        final String key = person.getName() + internal.getKey();
        map.put(key, internal.getValue());
    }
}

The main problem is that I can't use flatMap because I will lose previous information. Each created key is unique.

java-stream java-8 java
2 Answers

Well you could pass those along via a Pair (I have not compiled this though, but the idea should be there)

 list.stream()
    .flatMap(person -> person.getInternals()
                       .stream()
                       .map(internal -> 
                           Pair.of(person.getName() + internal.getKey(), internal.getValue()))
    .collect(Collectors.toMap(Pair::getLeft, Pair::getRight));
user_10593720

You can use collect directly and if you are sure that each created key is unique, as you mentioned, the accumulator and combiner are simple to write:

Map<String, String> map =
    list.stream().collect(HashMap::new,
                          (m, p) -> p.getInternals().forEach(i -> m.put(p.getName() + i.getKey(), i.getValue())),
                          Map::putAll);
user_15870460
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