From 993fbb3a0dc42603d4844c47b983374d6bd11edd Mon Sep 17 00:00:00 2001
From: Dmytro Nosan <dimanosan@gmail.com>
Date: Tue, 22 Oct 2024 23:54:56 +0300
Subject: [PATCH] Retain existing modules in JacksonAutoConfiguration

Previously, the default Jackson2ObjectMapperBuilderCustomizer
implementation did set the list of modules to use. This had the effect
of removing any modules that were registered programmatically by a
customizer with higher precedence.

This commit uses the variant of modulesToInstall that retain any
existing modules. It also adds a note in the documentation as this
behavior can be easily missed.

See gh-42836
---
 .../jackson/JacksonAutoConfiguration.java     |  2 +-
 .../JacksonAutoConfigurationTests.java        | 23 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration.java
index e388f4c3e5..3bc23da13d 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration.java
@@ -307,7 +307,7 @@ public class JacksonAutoConfiguration {
 			}
 
 			private void configureModules(Jackson2ObjectMapperBuilder builder) {
-				builder.modulesToInstall(this.modules.toArray(new Module[0]));
+				builder.modulesToInstall((modules) -> modules.addAll(this.modules));
 			}
 
 			private void configureLocale(Jackson2ObjectMapperBuilder builder) {
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfigurationTests.java
index 29dde38a97..06a937bc7b 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfigurationTests.java
@@ -73,6 +73,8 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.Primary;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
 import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -324,6 +326,16 @@ class JacksonAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void customModulesRegisteredByBuilderCustomizerWithHighestPrecedenceShouldBeRetained() {
+		this.contextRunner.withUserConfiguration(ModuleConfig.class, CustomModuleBuilderCustomizerConfig.class)
+			.run((context) -> {
+				ObjectMapper objectMapper = context.getBean(Jackson2ObjectMapperBuilder.class).build();
+				assertThat(context.getBean(CustomModule.class).getOwners()).contains(objectMapper);
+				assertThat(objectMapper.getRegisteredModuleIds()).contains("customizer-module");
+			});
+	}
+
 	@Test
 	void defaultSerializationInclusion() {
 		this.contextRunner.run((context) -> {
@@ -592,6 +604,17 @@ class JacksonAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class CustomModuleBuilderCustomizerConfig {
+
+		@Bean
+		@Order(Ordered.HIGHEST_PRECEDENCE)
+		Jackson2ObjectMapperBuilderCustomizer customModuleCustomizer() {
+			return (builder) -> builder.modulesToInstall(new SimpleModule("customizer-module"));
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class ObjectMapperBuilderConsumerConfig {