Isolate Jackson2ObjectMapperBuilder mutation

Previously, Jackson2ObjectMapperBuilder was a singleton bean. This
meant that if it was injected and mutated in one injection point,
usage in a subsequent injection point would see the previous
injection point's mutation which can lead to unexpected failures.

This commit updates the auto-configuration of the builder to make it
a protoype bean. Mutation of the builder that is intended to apply
globally should be made using a customizer.

Closes gh-17477

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration.java

@@ -54,6 +54,7 @@ import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Primary;
+import org.springframework.context.annotation.Scope;
 import org.springframework.core.Ordered;
 import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
 import org.springframework.util.Assert;
@@ -168,6 +169,7 @@ public class JacksonAutoConfiguration {
 	static class JacksonObjectMapperBuilderConfiguration {
 
 		@Bean
+		@Scope("prototype")
 		@ConditionalOnMissingBean
 		Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder(ApplicationContext applicationContext,
 				List<Jackson2ObjectMapperBuilderCustomizer> customizers) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfigurationTests.java

@@ -391,6 +391,16 @@ class JacksonAutoConfigurationTests {
 				});
 	}
 
+	@Test
+	void builderIsNotSharedAcrossMultipleInjectionPoints() {
+		this.contextRunner.withUserConfiguration(ObjectMapperBuilderConsumerConfig.class).run((context) -> {
+			ObjectMapperBuilderConsumerConfig consumer = context.getBean(ObjectMapperBuilderConsumerConfig.class);
+			assertThat(consumer.builderOne).isNotNull();
+			assertThat(consumer.builderTwo).isNotNull();
+			assertThat(consumer.builderOne).isNotSameAs(consumer.builderTwo);
+		});
+	}
+
 	private void assertParameterNamesModuleCreatorBinding(Mode expectedMode, Class<?>... configClasses) {
 		this.contextRunner.withUserConfiguration(configClasses).run((context) -> {
 			DeserializationConfig deserializationConfig = context.getBean(ObjectMapper.class)
@@ -479,6 +489,27 @@ class JacksonAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class ObjectMapperBuilderConsumerConfig {
+
+		Jackson2ObjectMapperBuilder builderOne;
+
+		Jackson2ObjectMapperBuilder builderTwo;
+
+		@Bean
+		String consumerOne(Jackson2ObjectMapperBuilder builder) {
+			this.builderOne = builder;
+			return "one";
+		}
+
+		@Bean
+		String consumerTwo(Jackson2ObjectMapperBuilder builder) {
+			this.builderTwo = builder;
+			return "two";
+		}
+
+	}
+
 	protected static final class Foo {
 
 		private String name;