Efficient way to iterate and copy the values of HashMap

Question

I want to convert:

Map<String, Map<String, List<Map<String, String>>>> inputMap 

to:

Map<String, Map<String, CustomObject>> customMap

inputMap is provided in the config and is ready but I need to customMap Format. CustomObject will be derived from List<Map<String, String>> using few lines of code in a function.

I have tried a normal way of iterating input map and copying key values in customMap. Is there any efficient way of doing that using Java 8 or some other shortcut?

Map<String, Map<String, List<Map<String, String>>>> configuredMap = new HashMap<>();
Map<String, Map<String, CustomObj>> finalMap = new HashMap<>();


for (Map.Entry<String, Map<String, List<Map<String, String>>>> attributeEntry : configuredMap.entrySet()) {
    Map<String, CustomObj> innerMap = new HashMap<>();
    for (Map.Entry<String, List<Map<String, String>>> valueEntry : attributeEntry.getValue().entrySet()) {
        innerMap.put(valueEntry.getKey(), getCustomeObj(valueEntry.getValue()));
    }
    finalMap.put(attributeEntry.getKey(), innerMap);
}

private CustomObj getCustomeObj(List<Map<String, String>> list) {
    return new CustomObj();
}

Answer 1

One solution is to stream the entrySet of inputMap, and then use Collectors#toMap twice (once for the outer Map, and once for the inner Map):

Map<String, Map<String, CustomObj>> customMap = inputMap.entrySet()
        .stream()
        .collect(Collectors.toMap(Function.identity(), entry -> {
            return entry.getValue()
                        .entrySet()
                        .stream()
                        .collect(Collectors.toMap(Function.identity(), 
                            entry -> getCustomeObj(entry.getValue())));
        }));