Add KotlinModule support and tests for schema generation in BeanOutputConverter (#3900)

Fixes #3900

Auto-cherry-pick to 1.0.x

Signed-off-by: Dmitry Sulman <[email protected]>

Author: dmitrysulman

spring-ai-model/src/main/java/org/springframework/ai/converter/BeanOutputConverter.java

@@ -37,7 +37,9 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import org.springframework.ai.model.KotlinModule;
 import org.springframework.ai.util.JacksonUtils;
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.lang.NonNull;
 
@@ -136,6 +138,11 @@ private void generateSchema() {
 				com.github.victools.jsonschema.generator.OptionPreset.PLAIN_JSON)
 			.with(jacksonModule)
 			.with(Option.FORBIDDEN_ADDITIONAL_PROPERTIES_BY_DEFAULT);
+
+		if (KotlinDetector.isKotlinReflectPresent()) {
+			configBuilder.with(new KotlinModule());
+		}
+
 		SchemaGeneratorConfig config = configBuilder.build();
 		SchemaGenerator generator = new SchemaGenerator(config);
 		JsonNode jsonNode = generator.generateSchema(this.type);

spring-ai-model/src/test/kotlin/org/springframework/ai/converter/BeanOutputConverterTests.kt

@@ -0,0 +1,58 @@
+package org.springframework.ai.converter
+
+import com.fasterxml.jackson.databind.ObjectMapper
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+class KotlinBeanOutputConverterTests {
+
+	private data class Foo(val bar: String, val baz: String?)
+	private data class FooWithDefault(val bar: String, val baz: Int = 10)
+
+	private val objectMapper = ObjectMapper()
+
+	@Test
+	fun `test Kotlin data class schema generation using getJsonSchema`() {
+		val converter = BeanOutputConverter(Foo::class.java)
+
+		val schemaJson = converter.jsonSchema
+
+		val schemaNode = objectMapper.readTree(schemaJson)
+
+		val required = schemaNode["required"]
+		assertThat(required).isNotNull
+		assertThat(required.toString()).contains("bar")
+		assertThat(required.toString()).doesNotContain("baz")
+
+		val properties = schemaNode["properties"]
+		assertThat(properties["bar"]["type"].asText()).isEqualTo("string")
+
+		val bazTypeNode = properties["baz"]["type"]
+		if (bazTypeNode.isArray) {
+			assertThat(bazTypeNode.toString()).contains("string")
+			assertThat(bazTypeNode.toString()).contains("null")
+		} else {
+			assertThat(bazTypeNode.asText()).isEqualTo("string")
+		}
+	}
+
+	@Test
+	fun `test Kotlin data class with default values`() {
+		val converter = BeanOutputConverter(FooWithDefault::class.java)
+
+		val schemaJson = converter.jsonSchema
+
+		val schemaNode = objectMapper.readTree(schemaJson)
+
+		val required = schemaNode["required"]
+		assertThat(required).isNotNull
+		assertThat(required.toString()).contains("bar")
+		assertThat(required.toString()).doesNotContain("baz")
+
+		val properties = schemaNode["properties"]
+		assertThat(properties["bar"]["type"].asText()).isEqualTo("string")
+
+		val bazTypeNode = properties["baz"]["type"]
+		assertThat(bazTypeNode.asText()).isEqualTo("integer")
+	}
+}