Transform and filter a Java Map with streams

Question

I have a Java Map that I\'d like to transform and filter. As a trivial example, suppose I want to convert all values to Integers then remove the odd entries.

Map         


        

Answer 1

Yes, you can map each entry to another temporary entry that will hold the key and the parsed integer value. Then you can filter each entry based on their value.

Map output =
    input.entrySet()
         .stream()
         .map(e -> new AbstractMap.SimpleEntry<>(e.getKey(), Integer.valueOf(e.getValue())))
         .filter(e -> e.getValue() % 2 == 0)
         .collect(Collectors.toMap(
             Map.Entry::getKey,
             Map.Entry::getValue
         ));

Note that I used Integer.valueOf instead of parseInt since we actually want a boxed int.

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If you have the luxury to use the StreamEx library, you can do it quite simply:

Map output =
    EntryStream.of(input).mapValues(Integer::valueOf).filterValues(v -> v % 2 == 0).toMap();