[java] Ignore duplicates when producing map using streams

I have encountered such a problem when grouping object, i always resolved them by a simple way: perform a custom filter using a java.util.Set to remove duplicate object with whatever attribute of your choice as bellow

Set<String> uniqueNames = new HashSet<>();
Map<String, String> phoneBook = people
                  .stream()
                  .filter(person -> person != null && !uniqueNames.add(person.getName()))
                  .collect(toMap(Person::getName, Person::getAddress));

Hope this helps anyone having the same problem !

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