No Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator

89

I am trying to consume an API using Retrofit and Jackson to deserialize. I am getting the onFailure error No Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator.

This question is tagged with android kotlin jackson retrofit2

~ Asked on 2018-11-07 14:29:25

The Best Answer is


81

I got here searching for this error:

No Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator

Nothing to do with Retrofit but if you are using Jackson this error got solved by adding a default constructor to the class throwing the error. More here: https://www.baeldung.com/jackson-exception

~ Answered on 2019-07-07 16:22:46


47

You need to use jackson-module-kotlin to deserialize to data classes. See here for details.

The error message above is what Jackson gives you if you try to deserialize some value into a data class when that module isn't enabled or, even if it is, when the ObjectMapper it uses doesn't have the KotlinModule registered. For example, take this code:

data class TestDataClass (val foo: String)

val jsonString = """{ "foo": "bar" }"""
val deserializedValue = ObjectMapper().readerFor(TestDataClass::class.java).readValue<TestDataClass>(jsonString)

This will fail with the following error:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `test.SerializationTests$TestDataClass` (although at least one Creator exists): cannot deserialize from Object value (no delegate- or property-based Creator)

If you change the code above and replace ObjectMapper with jacksonObjectMapper (which simply returns a normal ObjectMapper with the KotlinModule registered), it works. i.e.

val deserializedValue = jacksonObjectMapper().readerFor(TestDataClass::class.java).readValue<TestDataClass>(jsonString)

I'm not sure about the Android side of things, but it looks like you'll need to get the system to use the jacksonObjectMapper to do the deserialization.

~ Answered on 2018-11-07 14:34:34


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