feat : GraphQL 에서 기본적으로 지원하지 않는 Long, java.time 관련 타입 Scalars 생성 훅 설정 추가

놀이터(예제 코드 작성)/graphql-kotlin/src/main/kotlin/com/banjjoknim/graphqlkotlin/configuration/ExtendedScalarsConfiguration.kt

@@ -0,0 +1,107 @@
+package com.banjjoknim.graphqlkotlin.configuration
+
+import com.expediagroup.graphql.generator.hooks.SchemaGeneratorHooks
+import graphql.language.StringValue
+import graphql.scalars.ExtendedScalars
+import graphql.scalars.util.Kit.typeName
+import graphql.schema.Coercing
+import graphql.schema.CoercingParseLiteralException
+import graphql.schema.CoercingParseValueException
+import graphql.schema.CoercingSerializeException
+import graphql.schema.GraphQLScalarType
+import graphql.schema.GraphQLType
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+import java.time.LocalDate
+import java.time.LocalDateTime
+import java.time.LocalTime
+import java.time.format.DateTimeFormatter
+import kotlin.reflect.KClass
+import kotlin.reflect.KType
+
+/**
+ * - [Extended Scalars for graphql-java](https://github.com/graphql-java/graphql-java-extended-scalars)
+ *
+ * - [Cannot use java.util.Date](https://github.com/ExpediaGroup/graphql-kotlin/discussions/1198)
+ *
+ * - [GraphQL Kotlin - Extended Scalars](https://opensource.expediagroup.com/graphql-kotlin/docs/schema-generator/writing-schemas/scalars/#common-issues)
+ *
+ * - [GraphQL Kotlin - Generator Configuration & Hooks](https://opensource.expediagroup.com/graphql-kotlin/docs/schema-generator/customizing-schemas/generator-config)
+ */
+@Configuration
+class ExtendedScalarsConfiguration {
+    /**
+     * 아래와 같이 Bean으로 Hook을 등록해주면 Schema Generator가 Schema를 생성할 때 이 Bean에 정의된 Hook을 이용해서 Schema를 만든다.
+     */
+    @Bean
+    fun extendedScalarsHooks(): SchemaGeneratorHooks {
+        return object : SchemaGeneratorHooks {
+            override fun willGenerateGraphQLType(type: KType): GraphQLType? {
+                return when (type.classifier as? KClass<*>) {
+                    Long::class -> ExtendedScalars.GraphQLLong
+                    LocalDateTime::class -> localDateTimeScalar()
+                    LocalTime::class -> ExtendedScalars.LocalTime
+                    LocalDate::class -> ExtendedScalars.Date
+                    else -> null
+                }
+            }
+        }
+    }
+
+    /**
+     * Bean으로 ScalarType을 등록해주지 않으면 어플리케이션 실행시 스키마를 구성하는 단계(스키마에 포함될 타입중에서 LocalDateTime 이 포함되어 있는 경우)에서 아래와 같은 예외가 발생한다.
+     *
+     * ```
+     * graphql.AssertException: All types within a GraphQL schema must have unique names. No two provided types may have the same name.
+     * No provided type may have a name which conflicts with any built in types (including Scalar and Introspection types). You have redefined the type 'LocalDateTime' from being a 'GraphQLScalarType' to a 'GraphQLScalarType'
+     * ```
+     *
+     * @see graphql.scalars.datetime.DateTimeScalar
+     */
+    @Bean
+    fun localDateTimeScalar(): GraphQLScalarType? {
+        val coercing = object : Coercing<LocalDateTime, String> {
+            override fun serialize(dataFetcherResult: Any): String {
+                return when (dataFetcherResult) {
+                    is LocalDateTime -> DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(
+                        LocalDateTime.from(dataFetcherResult)
+                    )
+                    is String -> DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(
+                        LocalDateTime.parse(dataFetcherResult)
+                    )
+                    else -> throw CoercingSerializeException(
+                        "Expected something we can convert to 'java.time.LocalDateTime' but was '" +
+                            "${typeName(dataFetcherResult)}'."
+                    )
+                }
+            }
+
+            override fun parseValue(input: Any): LocalDateTime {
+                return when (input) {
+                    is LocalDateTime -> input
+                    is String -> LocalDateTime.parse(
+                        input.toString(),
+                        DateTimeFormatter.ISO_LOCAL_DATE_TIME
+                    )
+                    else -> throw CoercingParseValueException(
+                        "Expected a 'String' but was '" + "${typeName(input)}'."
+                    )
+                }
+            }
+
+            override fun parseLiteral(input: Any): LocalDateTime {
+                if (input !is StringValue) {
+                    throw CoercingParseLiteralException(
+                        "Expected AST type 'StringValue' but was '${typeName(input)}'."
+                    )
+                }
+                return LocalDateTime.parse(input.toString(), DateTimeFormatter.ISO_LOCAL_DATE_TIME)
+            }
+        }
+        return GraphQLScalarType.newScalar()
+            .name("LocalDateTime")
+            .description("Custom LocalDateTime Scalar")
+            .coercing(coercing)
+            .build()
+    }
+}