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Jack9

•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?


        ObjectMapper mapper = new ObjectMapper();
        MapType collectionType = mapper.getTypeFactory().constructMapType(HashMap.class, String.class, String[].class);
        HashMap<String,Object> result = mapper.convertValue(exampleDto, collectionType);

This is an initialization that is needed to pass the test. It does not survive additional field types, but it does avoid the conversion to ArrayList succinctly.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

There's an approach of mapper.read out some json, then deserialize that with https://github.com/Pretius/pretius-jddl/

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

There are a lot of discussions around a polymorphic deserializer here: https://github.com/FasterXML/jackson-databind/issues/1627 There was never a formal method. Lots of little pieces for subtypes and such.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

If you can make due with the bytes as an Object[], rather than a String[] , mapper.configure(DeserializationFeature.USE_JAVA_ARRAY_FOR_JSON_ARRAY, true);

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

The following seems overkill, but it works (more or less, no float etc) added as:

        
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(HashMap.class, new CustomDeSerializer());
mapper.registerModule(module);
HashMap<String,Object> result = mapper.convertValue(exampleDto, new TypeReference<>(){});

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

This was a long-winded way of saying "I don't know and don't care". GL with whatever.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

They implement a defaultSerializer which does not involve json

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

This is incorrect. Jackson provides a conversion API via convertValue.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

@JsonSerialize addresses this same X/Y problem, from a different direction. I don't understand the avoidance.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

I have another API that needs a HashMap and it can only handle primitive members and primitive arrays.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

This isn't relevant. The question is about methodology, not circumstance. Why I care is that I am trying to figure out a way to do it, beyond my current solution. Let's just assume I can't control the source datastructure (it's part of another API in jar), does that matter? No.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

I don't understand.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

[1,2,3] is simpler datatype that exists in JSON than ArrayList(){{ 1,2,3 }}. The question remains, other than a fairly robust deserializer to a mapper as a module, is there a simpler way?

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

I believe what is happening is that the serializer is called to make json, which is then tokenized with a json parser. Then the jackson json parser is used to make the HashMap.class, which has a default jackson serializer. In order to ensure type safety of each element of an array, it uses an ArrayList. So the String[] type disappears. Making a ~50ln deserializer works to coerce the type back to String[] - but that seems overkill. Is there any other way? I would imagine this has come up before for Jackson.

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•Created by Jack9 on 11/14/2024 in #java-help

Jackson Mapper - String[] conversion possible?

The test is to demonstrate the conversion to ArrayList. The question is how to convert a String[] property into a Hashmap<String, Object> with a <String, String[]> entry instead of the coerced <String, ArrayList<String>> entry.

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