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# Module Configuration
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Core module setup and configuration with extensive customization options through feature flags and builder patterns.
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## Capabilities
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### KotlinModule
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Main Jackson module class that integrates Kotlin support with Jackson's core functionality.
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```kotlin { .api }
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/**
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 * Main Jackson module class for Kotlin support
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 * @property reflectionCacheSize Size of the caches used for mapping objects (default: 512)
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 * @property nullToEmptyCollection Whether to deserialize null collections as empty
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 * @property nullToEmptyMap Whether to deserialize null maps as empty
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 * @property nullIsSameAsDefault Whether null values use Kotlin default values
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 * @property singletonSupport Whether to support Kotlin object singletons
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 * @property strictNullChecks Whether to check collection nullability
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 * @property kotlinPropertyNameAsImplicitName Whether to use Kotlin property names
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 * @property useJavaDurationConversion Whether to convert kotlin.time.Duration
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 */
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class KotlinModule private constructor(
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    val reflectionCacheSize: Int = 512,
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    val nullToEmptyCollection: Boolean = false,
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    val nullToEmptyMap: Boolean = false,
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    val nullIsSameAsDefault: Boolean = false,
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    val singletonSupport: Boolean = false,
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    val strictNullChecks: Boolean = false,
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    val kotlinPropertyNameAsImplicitName: Boolean = false,
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    val useJavaDurationConversion: Boolean = false
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) : SimpleModule
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```
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**Usage Examples:**
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```kotlin
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import com.fasterxml.jackson.module.kotlin.KotlinModule
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import com.fasterxml.jackson.databind.ObjectMapper
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// Create module with default settings
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val module = KotlinModule.Builder().build()
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val mapper = ObjectMapper().registerModule(module)
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// Create module with custom configuration
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val customModule = KotlinModule.Builder()
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    .enable(KotlinFeature.NullToEmptyCollection)
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    .enable(KotlinFeature.SingletonSupport)
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    .withReflectionCacheSize(1024)
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    .build()
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```
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### KotlinModule.Builder
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Builder class for configuring KotlinModule instances with method chaining.
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```kotlin { .api }
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/**
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 * Builder for configuring KotlinModule instances
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 */
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class Builder {
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    /** Set the size of reflection caches */
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    fun withReflectionCacheSize(size: Int): Builder
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    /** Enable a specific Kotlin feature */
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    fun enable(feature: KotlinFeature): Builder
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    /** Disable a specific Kotlin feature */
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    fun disable(feature: KotlinFeature): Builder
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    /** Configure a feature as enabled or disabled */
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    fun configure(feature: KotlinFeature, enabled: Boolean): Builder
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    /** Check if a feature is currently enabled */
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    fun isEnabled(feature: KotlinFeature): Boolean
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    /** Build the final KotlinModule instance */
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    fun build(): KotlinModule
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}
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```
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### KotlinFeature
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Enum defining all configurable features available in the Kotlin module.
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```kotlin { .api }
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/**
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 * Configurable features for the Kotlin module
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 */
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enum class KotlinFeature(internal val enabledByDefault: Boolean) {
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    /** Convert null collections to empty collections */
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    NullToEmptyCollection(enabledByDefault = false),
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    /** Convert null maps to empty maps */
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    NullToEmptyMap(enabledByDefault = false),
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    /** Use Kotlin default values for null parameters */
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    NullIsSameAsDefault(enabledByDefault = false),
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    /** Handle Kotlin object singletons properly */
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    SingletonSupport(enabledByDefault = false),
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    /** Check collection nullability (deprecated, use NewStrictNullChecks) */
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    StrictNullChecks(enabledByDefault = false),
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    /** Improved null checking with better performance */
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    NewStrictNullChecks(enabledByDefault = false),
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    /** Use Kotlin property names for serialization */
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    KotlinPropertyNameAsImplicitName(enabledByDefault = false),
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    /** Convert kotlin.time.Duration via java.time.Duration */
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    UseJavaDurationConversion(enabledByDefault = false)
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}
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```
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**Feature Configuration Examples:**
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```kotlin
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import com.fasterxml.jackson.module.kotlin.KotlinModule
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import com.fasterxml.jackson.module.kotlin.KotlinFeature
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// Enable null-to-empty collection conversion
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val module = KotlinModule.Builder()
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    .enable(KotlinFeature.NullToEmptyCollection)
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    .enable(KotlinFeature.NullToEmptyMap)
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    .build()
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// Configure strict null checking
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val strictModule = KotlinModule.Builder()
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    .enable(KotlinFeature.NewStrictNullChecks)
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    .build()
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// Support for Kotlin singletons
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val singletonModule = KotlinModule.Builder()
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    .enable(KotlinFeature.SingletonSupport)
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    .build()
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```
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### Class Extension
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Utility function for detecting Kotlin classes.
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```kotlin { .api }
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/**
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 * Extension function to check if a class is a Kotlin class
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 * @return true if the class is annotated with Kotlin's @Metadata annotation
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 */
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fun Class<*>.isKotlinClass(): Boolean
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```
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**Usage Examples:**
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```kotlin
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import com.fasterxml.jackson.module.kotlin.isKotlinClass
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data class KotlinClass(val name: String)
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class JavaClass { String name; }
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val isKotlin = KotlinClass::class.java.isKotlinClass() // true
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val isJava = JavaClass::class.java.isKotlinClass()     // false
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```
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## Exception Handling
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### MissingKotlinParameterException
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Specialized exception for missing Kotlin constructor parameters (deprecated in favor of more general Jackson exceptions).
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```kotlin { .api }
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/**
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 * Specialized exception for missing Kotlin constructor parameters
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 * @param parameter The missing Kotlin parameter (deprecated - not serializable)
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 * @param processor JsonParser instance where error occurred
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 * @param msg Error message
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 * @deprecated Use MismatchedInputException instead
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 */
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@Deprecated("Use MismatchedInputException instead")
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class MissingKotlinParameterException(
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    @Deprecated("KParameter is not serializable")
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    @Transient
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    val parameter: KParameter,
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    processor: JsonParser? = null,
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    msg: String
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) : InvalidNullException
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```