About the problem that property names in Jackson and definitions in Kotlin are sometimes different.

[k163377]

About current problems

Currently, in jackson-module-kotlin, property names on Jackson (e.g., property names in serialization results) may differ from their definitions in Kotlin.
Also, annotations on parameters do not work in this situation(#603).

Below is a summary of the situations in which this problem occur.

When the result of converting the name of a getter does not match the property name

This problem is especially likely to occur when the string converted from the generated getter name according to the Java Beans specification is at variance with the property name on Kotlin.
This is the case if the property name starts with an uppercase letter (#173), or if use a property name that starts with a single lowercase letter (#570), etc.

If the property visibility is internal

In this case, it is due to the fact that the name of the generated getter is given a suffix generated by Kotlin (see #71).

If the property name contains -.

Field names containing hyphens are truncated when serialized(#434).
This is a side effect of removing the random suffix given to the name of the getter generated for the value class (see #383).

Regarding workarounds that users can do.

Basically, it is recommended to use JsonProperty.
As mentioned above, annotations on parameters do not work in this case, so they must be added to getter or field.

data class Data(
+ @get:JsonProperty("fFoo")
- @JsonProperty("fFoo")
  val fFoo: Int
)

There are other ways to use annotations such as JvmField or JvmName.

Proposed modification of jackson-module-kotlin.

It is counter-intuitive behavior that the definition on Kotlin and the serialization result are different.
Therefore, we are considering adding an option to use the name on Kotlin in preference to the getter name during serialization.
If this option is enabled, it changes the processing of KNAI.findImplicitPropertyName.

Additional context

Example implementation of this option:
#451

Enabling this option increases reflection processing and will probably decrease processing speed.
Also, if this option is enabled, several behaviors are changed destructively.
For example, getter name changes with JvmName will be disabled, and annotations that previously did not work during serialization will work.
Therefore, this option cannot be enabled by default for the time being.

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Amendment: behavior of is-getter

A fix for the is-getter problem as reported in #340 will be released in 2.15.

[k163377]

This feature will be available in 2.16.