Field order mismatch after serialization and deserialization

[arvgord]

Search before asking

• I searched in the issues and found nothing similar.
• I searched in the issues of databind and other modules used and found nothing similar.
• I have confirmed that the problem only occurs when using Kotlin.

Describe the bug

I am encountering a problem where the field order is not preserved after serializing and deserializing objects in Jackson.

I need access to only one specific field (transactionId), while I want to pass the remaining fields as they are, preserving the order in which they appear. I expected the transactionId field order might change, but I did not expect the order of the other fields (a, b, c) to change, especially in the second and third tests (SecondObject and ThirdObject). The data inside the c array is preserved in the expected order, but the surrounding fields are re-ordered.

To Reproduce

Tested Objects:

@JsonAutoDetect(
    fieldVisibility = JsonAutoDetect.Visibility.ANY,
    getterVisibility = JsonAutoDetect.Visibility.NONE
)
class FirstObject {
    @field:JsonAnySetter
    @field:JsonAnyGetter
    val data: Map<String, Any?> = LinkedHashMap()

    val transactionId: String
        get() = data["transactionId"] as String
}

@JsonAutoDetect(
    fieldVisibility = JsonAutoDetect.Visibility.ANY,
    getterVisibility = JsonAutoDetect.Visibility.NONE
)
class SecondObject(
    val transactionId: String
) {
    @field:JsonAnySetter
    @field:JsonAnyGetter
    val data: Map<String, Any?> = LinkedHashMap()
}

@JsonAutoDetect(
    fieldVisibility = JsonAutoDetect.Visibility.ANY,
    getterVisibility = JsonAutoDetect.Visibility.NONE
)
class ThirdObject(
    val transactionId: String,
    @field:JsonAnySetter
    @field:JsonAnyGetter
    val data: Map<String, Any?> = LinkedHashMap()
)

Input JSON for tests:

{
  "b": 2,
  "a": 1,
  "transactionId": "test",
  "c": [
    {
      "id": "3",
      "value": "c"
    },
    {
      "id": "1",
      "value": "a"
    },
    {
      "id": "2",
      "value": "b"
    }
  ]
}

Test Case:

Here’s a test case to reproduce the issue. The following Kotlin test serializes and deserializes three different classes (FirstObject, SecondObject, and ThirdObject), comparing the serialized JSON with the original input JSON.
JacksonSortingTest.kt.

First Test Result (Passes):

The first test for FirstObject passes as expected, with the field order being preserved.

Failing Test Results:

Expected:

{
  "b": 2,
  "a": 1,
  "transactionId": "test",
  "c": [
    {
      "id": "3",
      "value": "c"
    },
    {
      "id": "1",
      "value": "a"
    },
    {
      "id": "2",
      "value": "b"
    }
  ]
}

For SecondObject was:

{
  "transactionId": "test",
  "a": 1,
  "b": 2,
  "c": [
    {
      "id": "3",
      "value": "c"
    },
    {
      "id": "1",
      "value": "a"
    },
    {
      "id": "2",
      "value": "b"
    }
  ]
}

For ThirdObject was:

{
  "transactionId": "test",
  "c": [
    {
      "id": "3",
      "value": "c"
    },
    {
      "id": "1",
      "value": "a"
    },
    {
      "id": "2",
      "value": "b"
    }
  ],
  "a": 1,
  "b": 2
}

Repository for Reproduction:
You can find a repository with the full reproduction of the issue at jackson-databind-sorting-issue.

Expected behavior

For SecondObject and ThirdObject, after serializing the object back to JSON, I expect the transactionId field to appear at the top, followed by the fields b, a, and c, in the exact order they were present when the JSON was deserialized into SecondObject and ThirdObject.

Versions

Kotlin: 2.0.0
Jackson-module-kotlin: 2.17.2
Jackson-databind: 2.17.2

Additional context

This issue is a duplicate of 4751. I'm trying to reproduce it with Java, but it seems like all the described cases are specific to Kotlin

[cowtowncoder]

Quick question: version affected is listed as 2.17.2 -- but how about 2.18.0.

Or, assuming 2.18.0 affected, would it be possible to test with 2.18.1-SNAPSHOT (of both jackson-databind and jackson-module-kotlin -- from Sonatype OSS Snapshots or locally built from 2.18 branches).
The reason I suggest this is because there have now been multiple small but significant fixes in 2.18 branch wrt any-setters so there is non-trivial chance this might be of one of fixes from:

https://github.com/FasterXML/jackson/wiki/Jackson-Release-2.18.1

and in particular, one of:

• deserialized JsonAnySetter field is null  jackson-databind#4508
• @JsonAnySetter on field ignoring unrecognized properties if they are declared before the last recognized properties in JSON jackson-databind#4639

[arvgord]

Quick question: version affected is listed as 2.17.2 -- but how about 2.18.0.

For version 2.18.0 I created another issue #843 where serialization was broken.

[k163377]

@arvgord
Like comment #843, could you please check if it is possible to reproduce it only with Java?

[arvgord]

@k163377, thank you! I was able to fully reproduce the incorrect sorting behavior in Java using your code (test file). I reopened the issue in jackson-databind. I close this issue.