Scala BigInt is converted to Double when converting the object to Map[String, Any]

[Saransh0905]

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When using Jackson ObjectMapper to convert Scala objects to Map[String, Any], numeric fields defined as BigInt are converted to Double instead of BigInteger or remaining as BigInt, causing precision loss.

This issue is not about regression across versions, but about undesired numeric coercion from a large integer to a Double.

We were using jackson 2.13.2 and in that Scala BigInt is converted to Long while deserializing at this line
https://github.com/FasterXML/jackson-databind/blame/87014ed5f3dfc1dcc21b704c2ce117266780c166/src/main/java/com/fasterxml/jackson/databind/util/TokenBuffer.java#L1849

In Jackson 2.15.2, this has beed changed and the BigInt value is converted to Double type. The change is done here:
https://github.com/FasterXML/jackson-databind/blame/74a57b2f6cd3b6e0fe2a61ed16734f15ba2abc95/src/main/java/com/fasterxml/jackson/databind/util/TokenBuffer.java#L1936

The serialisation part is same in both the version. But diff is while deserialisations. I wanted to understand if this is intentional or not? How can I fix this?

Version Information

2.15.2

Reproduction

case class A(b: BigInt = BigInt("9223372036854775808"))
val obj = A()
val map = objectMapper.convertValue(obj, classOf[Map[String, Any]])
println(map("b")) // 9.223372036854776E18 (Double) instead of BigInt or BigInteger

Expected behavior

BigInt in Scala should be treated a BigInteger in Java.

Additional context

No response

[pjfanning]

If you use a generic map, you cannot expect us to guess that you want a BigInt. You can write a custom deserialize if you don't like the default behaviour.

[Saransh0905]

The behaviour is changed from 2.13.2 to 2.15.2, which is a minor version change. That's why I thought it might be a bug.
Can you provide a sample for custom deserialize and how to register it?

[pjfanning]

https://www.baeldung.com/jackson-custom-serialization

You can also just take the map returned and write a function call the .intValue() on the double.

I would recommend that you use a strongly typed case class instead of using a Map as your target.

[Saransh0905]

Thanks for the support @pjfanning.

[cowtowncoder]

Since this is related to Scala type(s), it belongs to jackson-module-scala repo (https://github.com/FasterXML/jackson-module-scala/): I will transfer.

[cowtowncoder]

@pjfanning I suspect you won't have much interest in making changes, but moved it here since it should have been filed here (feel free to close).