Merge pull request #44040 from nosan

* pr/44040:
  Polish "Add property to configure Spring MVC default content types"
  Add property to configure Spring MVC default content types

Closes gh-44040

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration.java

@@ -76,6 +76,7 @@ import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.util.AntPathMatcher;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.CollectionUtils;
 import org.springframework.validation.DefaultMessageCodesResolver;
 import org.springframework.validation.MessageCodesResolver;
 import org.springframework.validation.Validator;
@@ -271,8 +272,12 @@ public class WebMvcAutoConfiguration {
 			if (contentnegotiation.getParameterName() != null) {
 				configurer.parameterName(contentnegotiation.getParameterName());
 			}
-			Map<String, MediaType> mediaTypes = this.mvcProperties.getContentnegotiation().getMediaTypes();
+			Map<String, MediaType> mediaTypes = contentnegotiation.getMediaTypes();
 			mediaTypes.forEach(configurer::mediaType);
+			List<MediaType> defaultContentTypes = contentnegotiation.getDefaultContentTypes();
+			if (!CollectionUtils.isEmpty(defaultContentTypes)) {
+				configurer.defaultContentType(defaultContentTypes.toArray(new MediaType[0]));
+			}
 		}
 
 		@Bean

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcProperties.java

@@ -17,7 +17,9 @@
 package org.springframework.boot.autoconfigure.web.servlet;
 
 import java.time.Duration;
+import java.util.ArrayList;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
@@ -306,6 +308,11 @@ public class WebMvcProperties {
 		 */
 		private boolean favorParameter = false;
 
+		/**
+		 * Query parameter name to use when "favor-parameter" is enabled.
+		 */
+		private String parameterName;
+
 		/**
 		 * Map file extensions to media types for content negotiation. For instance, yml
 		 * to text/yaml.
@@ -313,9 +320,10 @@ public class WebMvcProperties {
 		private Map<String, MediaType> mediaTypes = new LinkedHashMap<>();
 
 		/**
-		 * Query parameter name to use when "favor-parameter" is enabled.
+		 * List of default content types to be used when no specific content type is
+		 * requested.
 		 */
-		private String parameterName;
+		private List<MediaType> defaultContentTypes = new ArrayList<>();
 
 		public boolean isFavorParameter() {
 			return this.favorParameter;
@@ -325,6 +333,14 @@ public class WebMvcProperties {
 			this.favorParameter = favorParameter;
 		}
 
+		public String getParameterName() {
+			return this.parameterName;
+		}
+
+		public void setParameterName(String parameterName) {
+			this.parameterName = parameterName;
+		}
+
 		public Map<String, MediaType> getMediaTypes() {
 			return this.mediaTypes;
 		}
@@ -333,12 +349,12 @@ public class WebMvcProperties {
 			this.mediaTypes = mediaTypes;
 		}
 
-		public String getParameterName() {
-			return this.parameterName;
+		public List<MediaType> getDefaultContentTypes() {
+			return this.defaultContentTypes;
 		}
 
-		public void setParameterName(String parameterName) {
-			this.parameterName = parameterName;
+		public void setDefaultContentTypes(List<MediaType> defaultContentTypes) {
+			this.defaultContentTypes = defaultContentTypes;
 		}
 
 	}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -79,6 +79,7 @@ import org.springframework.format.Printer;
 import org.springframework.format.support.FormattingConversionService;
 import org.springframework.http.CacheControl;
 import org.springframework.http.HttpHeaders;
+import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.test.util.ReflectionTestUtils;
@@ -86,6 +87,7 @@ import org.springframework.util.StringUtils;
 import org.springframework.validation.Validator;
 import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
 import org.springframework.web.accept.ContentNegotiationManager;
+import org.springframework.web.accept.FixedContentNegotiationStrategy;
 import org.springframework.web.accept.ParameterContentNegotiationStrategy;
 import org.springframework.web.bind.annotation.ControllerAdvice;
 import org.springframework.web.bind.support.ConfigurableWebBindingInitializer;
@@ -577,6 +579,22 @@ class WebMvcAutoConfigurationTests {
 			});
 	}
 
+	@Test
+	void customDefaultContentTypes() {
+		this.contextRunner
+			.withPropertyValues("spring.mvc.contentnegotiation.default-content-types:application/json,application/xml")
+			.run((context) -> {
+				RequestMappingHandlerAdapter adapter = context.getBean(RequestMappingHandlerAdapter.class);
+				ContentNegotiationManager contentNegotiationManager = (ContentNegotiationManager) ReflectionTestUtils
+					.getField(adapter, "contentNegotiationManager");
+				assertThat(contentNegotiationManager).isNotNull();
+				assertThat(contentNegotiationManager.getStrategy(FixedContentNegotiationStrategy.class))
+					.extracting(FixedContentNegotiationStrategy::getContentTypes)
+					.asInstanceOf(InstanceOfAssertFactories.list(MediaType.class))
+					.containsExactly(MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML);
+			});
+	}
+
 	@Test
 	void formContentFilterIsAutoConfigured() {
 		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(OrderedFormContentFilter.class));