fix(kotlin-client): use Jackson 3 builder API in Serializer template

Jackson 3 ObjectMapper is immutable — no more chaining .configure()
and .setSerializationInclusion(). Use jsonMapper {} builder DSL with:
- changeDefaultPropertyInclusion for NON_ABSENT inclusion
- enable/disable for DateTimeFeature, EnumFeature, DeserializationFeature
- addModule(kotlinModule()) instead of jacksonObjectMapper()

Author: yonatankarp

modules/openapi-generator/src/main/resources/kotlin-client/jvm-common/infrastructure/Serializer.kt.mustache

@@ -30,19 +30,24 @@ import kotlinx.datetime.LocalTime
 import java.util.UUID
 {{/gson}}
 {{#jackson}}
+{{^useJackson3}}
 import {{jacksonPackage}}.databind.DeserializationFeature
 import {{jacksonPackage}}.databind.ObjectMapper
-{{^useJackson3}}
 import {{jacksonPackage}}.databind.SerializationFeature
+import com.fasterxml.jackson.annotation.JsonInclude
+import {{jacksonPackage}}.module.kotlin.jacksonObjectMapper
 {{/useJackson3}}
 {{#useJackson3}}
+import {{jacksonPackage}}.databind.DeserializationFeature
+import {{jacksonPackage}}.databind.ObjectMapper
 import {{jacksonPackage}}.databind.cfg.DateTimeFeature
 {{#enumUnknownDefaultCase}}
 import {{jacksonPackage}}.databind.cfg.EnumFeature
 {{/enumUnknownDefaultCase}}
-{{/useJackson3}}
 import com.fasterxml.jackson.annotation.JsonInclude
-import {{jacksonPackage}}.module.kotlin.jacksonObjectMapper
+import {{jacksonPackage}}.module.kotlin.jsonMapper
+import {{jacksonPackage}}.module.kotlin.kotlinModule
+{{/useJackson3}}
 {{/jackson}}
 {{#kotlinx_serialization}}
 import java.math.BigDecimal
@@ -128,27 +133,34 @@ import java.util.concurrent.atomic.AtomicLong
     }
 {{/gson}}
 {{#jackson}}
+{{^useJackson3}}
     @JvmStatic
     val jacksonObjectMapper: ObjectMapper = jacksonObjectMapper()
-        {{^useJackson3}}
         .findAndRegisterModules()
-        {{/useJackson3}}
         .setSerializationInclusion(JsonInclude.Include.NON_ABSENT)
         {{#enumUnknownDefaultCase}}
-        {{#useJackson3}}
-        .configure(EnumFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE, true)
-        {{/useJackson3}}
-        {{^useJackson3}}
         .configure(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE, true)
-        {{/useJackson3}}
         {{/enumUnknownDefaultCase}}
-        {{#useJackson3}}
-        .configure(DateTimeFeature.WRITE_DATES_AS_TIMESTAMPS, false)
-        {{/useJackson3}}
-        {{^useJackson3}}
         .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
-        {{/useJackson3}}
         .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, {{failOnUnknownProperties}})
+{{/useJackson3}}
+{{#useJackson3}}
+    @JvmStatic
+    val jacksonObjectMapper: ObjectMapper = jsonMapper {
+        addModule(kotlinModule())
+        changeDefaultPropertyInclusion { it.withValueInclusion(JsonInclude.Include.NON_ABSENT) }
+        {{#enumUnknownDefaultCase}}
+        enable(EnumFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE)
+        {{/enumUnknownDefaultCase}}
+        disable(DateTimeFeature.WRITE_DATES_AS_TIMESTAMPS)
+        {{#failOnUnknownProperties}}
+        enable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
+        {{/failOnUnknownProperties}}
+        {{^failOnUnknownProperties}}
+        disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
+        {{/failOnUnknownProperties}}
+    }
+{{/useJackson3}}
 {{/jackson}}
 {{#kotlinx_serialization}}
     private var isAdaptersInitialized = false

modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinClientCodegenModelTest.java

@@ -956,7 +956,7 @@ public void shouldGenerateJackson3Imports() throws IOException {
 
         Path serializerPath = Paths.get(outputPath + "/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt");
         TestUtils.assertFileContains(serializerPath, "import tools.jackson.databind.ObjectMapper");
-        TestUtils.assertFileContains(serializerPath, "import tools.jackson.module.kotlin.jacksonObjectMapper");
+        TestUtils.assertFileContains(serializerPath, "import tools.jackson.module.kotlin.jsonMapper");
         TestUtils.assertFileNotContains(serializerPath, "com.fasterxml.jackson.databind");
     }
 

samples/client/petstore/kotlin-jackson3/gradlew

@@ -5,13 +5,16 @@ import tools.jackson.databind.ObjectMapper
 import tools.jackson.databind.cfg.DateTimeFeature
 import tools.jackson.databind.cfg.EnumFeature
 import com.fasterxml.jackson.annotation.JsonInclude
-import tools.jackson.module.kotlin.jacksonObjectMapper
+import tools.jackson.module.kotlin.jsonMapper
+import tools.jackson.module.kotlin.kotlinModule
 
 object Serializer {
     @JvmStatic
-    val jacksonObjectMapper: ObjectMapper = jacksonObjectMapper()
-        .setSerializationInclusion(JsonInclude.Include.NON_ABSENT)
-        .configure(EnumFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE, true)
-        .configure(DateTimeFeature.WRITE_DATES_AS_TIMESTAMPS, false)
-        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
+    val jacksonObjectMapper: ObjectMapper = jsonMapper {
+        addModule(kotlinModule())
+        changeDefaultPropertyInclusion { it.withValueInclusion(JsonInclude.Include.NON_ABSENT) }
+        enable(EnumFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE)
+        disable(DateTimeFeature.WRITE_DATES_AS_TIMESTAMPS)
+        disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
+    }
 }