How to convert a JSON string to a Map<String, Set<String>> with Jackson JSON

Question

I am aware of the implementation which converts JSON string to a Map<String, String> through :

public <T1, T2> HashMap<T1, T2> getMapFromJson(String json, Class<T1> keyClazz, Class<T2> valueClazz) throws TMMIDConversionException {
    if (StringUtils.isEmpty(json)) {
        return null;
    }
    try {
        ObjectMapper mapper = getObjectMapper();
        HashMap<T1, T2> map = mapper.readValue(json, TypeFactory.defaultInstance().constructMapType(HashMap.class, keyClazz, valueClazz));
        return map;
    } catch (Exception e) {
        Logger.error(e.getMessage(), e.getCause());
    }
} 

But I cannot extend it to convert my JSON to a Map<String, Set<String>>. The above method fails, obviously, as it breaks the Set items and puts in the list. Need some help here!! Thanks

Sample JSON String is as below. This JSOn has to converted to a Map<String, Set<CustomClass>>.

{
    "0": [
        {
            "cid": 100,
            "itemId": 0,
            "position": 0
        }
    ],
    "1": [
        {
            "cid": 100,
            "itemId": 1,
            "position": 0
        }
    ],
    "7": [
        {
            "cid": 100,
            "itemId": 7,
            "position": -1
        },
        {
            "cid": 140625,
            "itemId": 7,
            "position": 1
        }
    ],
    "8": [
        {
            "cid": 100,
            "itemId": 8,
            "position": 0
        }
    ],
    "9": [
        {
            "cid": 100,
            "itemId": 9,
            "position": 0
        }
    ]
}

Answer 1

Try this:

JavaType setType = mapper.getTypeFactory().constructCollectionType(Set.class, CustomClass.class);
JavaType stringType = mapper.getTypeFactory().constructType(String.class);
JavaType mapType = mapper.getTypeFactory().constructMapType(Map.class, stringType, setType);

String outputJson = mapper.readValue(json, mapType)