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
        }
    ]
}

The JSON would help...

Boris the Spider
– Boris the Spider

2014-12-17 10:22:00 +00:00
Commented Dec 17, 2014 at 10:22 — Boris the Spider
– Boris the Spider, Commented Dec 17, 2014 at 10:22
I have added a sample JSON. Thanks.

Nihal Sharma
– Nihal Sharma

2014-12-17 10:34:34 +00:00
Commented Dec 17, 2014 at 10:34 — Nihal Sharma
– Nihal Sharma, Commented Dec 17, 2014 at 10:34
And how would that map to a Multimap?

Boris the Spider
– Boris the Spider

2014-12-17 10:35:15 +00:00
Commented Dec 17, 2014 at 10:35 — Boris the Spider
– Boris the Spider, Commented Dec 17, 2014 at 10:35

Ilya Ovesnov · Accepted Answer · 2014-12-17 23:00:33Z

24

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)

answered Dec 17, 2014 at 23:00

Ilya Ovesnov

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Comments

StaxMan · Accepted Answer · 2014-12-18 00:06:25Z

1

Unfortunately Class really can not express generic types; so if your value type is generic (like Set<String>), you need to pass JavaType instead. And that can be used to construct structured JavaType instances as well.

answered Dec 18, 2014 at 0:06

StaxMan

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