在 Springboot Java 中维护键值映射对的最佳方法

Question

I want to know the best way to handle key-value mapping in a Springboot API.

The request of the API is as:

{
  "a": "1",
  "b": "b"
}

This API then calls a downstream API. But before it does that I need to convert the values of the fields a and b. The conversion would be as per:

For field a:
1 -> One,
2 -> Two,
3 -> TATA

for fields b:
b -> beta,
a -> alpha,
c -> c

Both of the above mappings are constant(wont change throughout) and hence need to be initialized and maintained in our API. Now once the mapping takes place the request to the downstream API will look like.

{ 
  "a" : "One",
  "b" : "beta"
}

ie 1 is mapped to One for field a, and b is mapped to beta for field b; based on the key value mapping mentioned above.

Need to know the best practice in Java and Spring boot to achieve this. How do I maintain the mapping table, initialize it just once and convert incoming API requests to corresponding values at runtime.

Can't use enum because some keys are numerical. If Hash Map and Hast table are my best bets, then how do I initialize them and maintain them throughout, since the mapping is constant don't want to create them again and again for each API call? Where do I read the key-value pairs from to initialize the hashmap/table?

Answer 1

You could keep your translations in code in a private static final field, and initialize it in a static initialization block:

private static final Map<String, Map<String, String>> TRANSLATIONS_PER_KEY = new HashMap<>();

static {
    Map<String, String> translateForA = new HashMap<>();
    translateForA.put("1", "One");
    ...
    TRANSLATIONS_PER_KEY.put("a", translateForA);
    ...
}

Then you could do the translation using Guava Maps.transformEntries() :

    Map<String, String> translated =
            Maps.transformEntries(input, (key, value) ->
                    TRANSLATIONS_PER_KEY.get(key)
                            .getOrDefault(value));

If you want to avoid NullPointers, and return the original value if there is no translation, you could do it like this:

    Map<String, String> translated =
            Maps.transformEntries(input, (key, value) ->
                    TRANSLATIONS_PER_KEY.getOrDefault(key, emptyMap())
                            .getOrDefault(value, value));

Answer 2

You may create enum for all mappings with pares

@AllArgsConstructor
@Getter
public enum AType {
    ONE("One", "1"),
    TWO("Two", "2"),
    TATA("TATA", "3");

    private String translation;
    private String mapping;


    public String of(String v) {
        for (AType aType : values()) {
            if (aType.getMapping().equals(v)) {
                return translation;
            }
        }
        throw new IllegalArgumentException("try again");
    }
}

and new enum for b