Convert type X to Y in Map<K, Map<V, X>> using Java Stream API

Question

I want to convert inner map from map of maps.

Old map: Map<String, Map<LocalDate, Integer>> Integer means seconds

New map: Map<String, Map<LocalDate, Duration>>

I have tried created new inner map, but got an error

Error: java: no suitable method found for putAll(java.util.stream.Stream<java.lang.Object>) method java.util.Map.putAll(java.util.Map<? extends java.time.LocalDate,? extends java.time.Duration>) is not applicable

oldMap.entrySet().stream()
            .collect(Collectors.toMap(Map.Entry::getKey,
                e -> new HashMap<LocalDate, Duration>() {{
                    putAll(
                        e.getValue().entrySet().stream()
                            .map(x -> new HashMap.SimpleEntry<LocalDate, Duration>
                                (x.getKey(), Duration.ofSeconds(x.getValue())))
                    );
                }}
            ));

Answer 1

If you want compact code, you may use

Map<String, Map<LocalDate, Duration>> newMap = new HashMap<>();
oldMap.forEach((s,o) -> o.forEach((d, i) ->
    newMap.computeIfAbsent(s, x->new HashMap<>()).put(d, Duration.ofSeconds(i))));

If you want to avoid unnecessary hash operations, you may expand it a bit

Map<String, Map<LocalDate, Duration>> newMap = new HashMap<>();
oldMap.forEach((s,o) -> {
    Map<LocalDate, Duration> n = new HashMap<>();
    newMap.put(s, n);
    o.forEach((d, i) -> n.put(d, Duration.ofSeconds(i)));
});