Is there any way to extract Map's values?

Question

I try to extract values from the below data type. Map<String, Map<String, Integer>>, The sample data is like this.

1. ("aaa", Map("bbb",333) )
2. ("ddd", Map("ccc",444) )

Result that I want

HashMap 
key : bbb, value : 333 
key : ccc, value : 444

I tried

mapData.values().stream()
       .collect(Collectors.toMap(Map.Entry::getKey,Map.Entry::getValue))

but got failed. Is there any good way to extract the values part as Map in the nested Map ?

Answer 1

You need to flatMap your entries of the inner map -

Map<String, Integer> output = map.values().stream()
        .flatMap(m -> m.entrySet().stream())
        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

Answer 2

Simple way is:

Map<String,Integer> map = new HashMap<>();
mapData.values().forEach(map::putAll);

or

mapData.values().stream().collect(HashMap::new, HashMap::putAll,Map::putAll);