First two characters of property name must be lowercase due to Java restrictions

I discovered today by chance that an old restriction from Java means that you cannot have uppercase characters in the first two characters of a JSON/Kotlin property.

Consider this self-contained test case:

import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue
import org.junit.Assert
import org.junit.Test

class DataClassTest2 {

    data class DataClass1(val zName: String)

    data class DataClass2(val zname: String)

    private val jsonData1 = """
        {
            "zName": "my name"
        }
        """

    private val jsonData2 = """
        {
            "zname": "my name"
        }
        """

    @Test
    fun testJsonParsing1() {
        val mapper = jacksonObjectMapper()
        val dataClass1 = mapper.readValue<DataClass1>(jsonData1)
        Assert.assertEquals("my name", dataClass1.zName)
    }

    @Test
    fun testJsonParsing2() {
        val mapper = jacksonObjectMapper()
        val dataClass2 = mapper.readValue<DataClass2>(jsonData2)
        Assert.assertEquals("my name", dataClass2.zname)
    }
}

The first test fails and the second passes.

This is because of this and by reference this.

However in the world of Kotlin, we are several steps removed from Java beans or indeed the underlying setters/getters that Kotlin automatically generates, and this behaviour doesn’t make a great deal of sense. It was only by accident that I discovered it.

Please consider whether there’s an opportunity to bypass this issue via the Kotlin module.

[akosmenyhert]

Use the @JsonProperty annotation to the accessor methods.

For example: @get:JsonProperty("ID") val id: String = ""

[MaiconCanedo]

This can be useful: https://github.com/FasterXML/jackson-docs/wiki/JacksonMixInAnnotations