Converting a map of string key-values to enum key-values in Java

Question

I have a map read from my static config in the following format: Map<String, Map<String, List<String>>> dependentPluginEntityMapString. The string values in this map are actually from ENUMs and the correct and required representation of the map is Map<ENUM_A, Map<ENUM_A, List<ENUM_B>>>.

ENUM_A {
 APPLE, BANANA
}

ENUM_B {
ONION, RADDISH
}

How can I convert the map of strings to the one with enums Map<ENUM_A, Map<ENUM_A, List<ENUM_B>>> for more type safety?

I know, I can iterate on the string map (using for or streams) and create a new map with enums as required but looking for a better/more efficient and an elegant way of doing that?

This is my brute solution. Can i do better?

final Map<ENUM_A, Map<ENUM_A, List<ENUM_B>>> dependentPluginEntityMap = new HashMap<>();

        for (Map.Entry<String, Map<String, List<String>>> dependentPluginEntry:
                dependentPluginEntityMapFromAppConfig.entrySet()) {
            final Map<ENUM_A, List<ENUM_B>> independentPluginMapForEntry = new HashMap<>();

            if (MapUtils.isNotEmpty(dependentPluginEntry.getValue())) {
                for (Map.Entry<String, List<String>> independentPluginEntry:
                        dependentPluginEntry.getValue().entrySet()) {
                    if (CollectionUtils.isNotEmpty(independentPluginEntry.getValue())) {
                        independentPluginMapForEntry.put(ENUM_A.valueOf(independentPluginEntry.getKey()),
                                independentPluginEntry.getValue().stream().map(value -> ENUM_B.valueOf(value))
                                        .collect(Collectors.toList()));
                    }
                }
            }
            dependentPluginEntityMap.put(ENUM_A.valueOf(dependentPluginEntry.getKey()),
                    independentPluginMapForEntry);
        }

Should I convert the map of strings to ENUMMAP , instead of map with enum keys? Will it work with my nested map structure?

Any leads apprecciated.

Your case is made complex because your enum constants are members of different types. In particular, EnumMap requires that the constants that serve as keys in the map all be members of the same enum class. It is not possible to create an EnumMap with a non-concrete type token, unfortunately. A workaround for your use case would be to make the enum types implement a common interface, and then to use the interface type as the map keys. You will not be able to use the EnumMap class in this solution,, though. — scottb
– scottb, Commented May 17, 2021 at 17:19
Okay thanks. I am also planning to use Maps only. My main question is actually the #1, on how I can convert the maps elegantly? — user2696258
– user2696258, Commented May 17, 2021 at 17:56

DuncG · Accepted Answer · 2021-11-15 11:21:59Z

1

Multi-level Map conversions are easier if you define simple utility methods to manage transformation from Map<K,V> to Map<X,Y> and List<X> to List<Y>:

static <X,Y> List<Y> toList(List<X> list, Function<X,Y> valueMapper) {
    return list.stream().map(valueMapper).toList();
}

static <K,V,X,Y> Map<X, Y> toMap(Map<K, V> map, Function<K,X> keyMapper, Function<V,Y> valueMapper) {
    return map.entrySet().stream()
              .collect(Collectors.toMap(entry -> keyMapper.apply(entry.getKey()),
                                        entry -> valueMapper.apply(entry.getValue())));
}

With these definitions your transformation is reduced to applications of the above:

Map<String, Map<String, List<String>>> in = Map.of(
        "APPLE",   Map.of("APPLE", List.of("RADDISH")
                         ,"BANANA", List.of("ONION", "RADDISH"))
        ,"BANANA", Map.of("APPLE", List.of("ONION", "RADDISH")
                         , "BANANA", List.of("ONION"))
        );

Map<ENUM_A, Map<ENUM_A, List<ENUM_B>>> map  
    = toMap(in, ENUM_A::valueOf,
                m -> toMap(m, ENUM_A::valueOf, 
                              list -> toList(list, ENUM_B::valueOf)));

=>
map ={BANANA={BANANA=[ONION]
             , APPLE=[ONION, RADDISH]}
    , APPLE={BANANA=[ONION, RADDISH]
             , APPLE=[RADDISH]}}

edited Nov 15, 2021 at 11:21

answered May 17, 2021 at 18:00

DuncG

16.3k3 gold badges31 silver badges44 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

user2696258 Over a year ago

is using streams better, always? I would want to have a more cleaner code with almost same performance as these map sizes will not be large for sure. Hence, clean and simple is what I am aiming.

user2696258 Over a year ago

Can I go more cleaner impl than what I have added, using streams?

DuncG Over a year ago

@user2696258 the answer is now refactored into simpler components to avoid duplicating the same code to deal with both maps.

Collectives™ on Stack Overflow

Converting a map of string key-values to enum key-values in Java

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related