How to log filtered values in Java Streams

Question

I have a requirement to log/sysout the filtered values in Java Streams. I am able to log/sysout the non-filtered value using peek() method

Answer 1

You could use

Map> map = persons.stream()
    .collect(Collectors.partitioningBy(p -> "John".equals(p.getName())));
System.out.println("filtered: " + map.get(true));
List result = map.get(false);

or, if you prefer a single-statement form:

List result = persons.stream()
    .collect(Collectors.collectingAndThen(
        Collectors.partitioningBy(p -> "John".equals(p.getName())),
        map -> {
            System.out.println("filtered: " + map.get(true));
            return map.get(false);
        }));