Introduce hints support in advices

This commit introduces RequestBodyAdvice#determineReadHints and
ResponseBodyAdvice#determineWriteHints in order to be able to support
SmartHttpMessageConverter hints, as well as related `@JsonView`
support.

See gh-33798

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMappingJacksonResponseBodyAdvice.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -20,6 +20,7 @@ import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.http.MediaType;
+import org.springframework.http.converter.AbstractJacksonHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter;
 import org.springframework.http.converter.json.MappingJacksonValue;
@@ -39,7 +40,8 @@ public abstract class AbstractMappingJacksonResponseBodyAdvice implements Respon
 
 	@Override
 	public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
-		return AbstractJackson2HttpMessageConverter.class.isAssignableFrom(converterType);
+		return AbstractJacksonHttpMessageConverter.class.isAssignableFrom(converterType) ||
+				AbstractJackson2HttpMessageConverter.class.isAssignableFrom(converterType);
 	}
 
 	@Override
@@ -50,6 +52,9 @@ public abstract class AbstractMappingJacksonResponseBodyAdvice implements Respon
 		if (body == null) {
 			return null;
 		}
+		if (AbstractJacksonHttpMessageConverter.class.isAssignableFrom(converterType)) {
+			return body;
+		}
 		MappingJacksonValue container = getOrCreateContainer(body);
 		beforeBodyWriteInternal(container, contentType, returnType, request, response);
 		return container;

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -175,7 +175,7 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 			ResolvableType targetResolvableType = null;
 			message = new EmptyBodyCheckingHttpInputMessage(inputMessage);
 			for (HttpMessageConverter<?> converter : this.messageConverters) {
-				Class<HttpMessageConverter<?>> converterClass = (Class<HttpMessageConverter<?>>) converter.getClass();
+				Class<? extends HttpMessageConverter<?>> converterClass = (Class<? extends HttpMessageConverter<?>>) converter.getClass();
 				ConverterType converterTypeToUse = null;
 				if (converter instanceof GenericHttpMessageConverter<?> genericConverter) {
 					if (genericConverter.canRead(targetType, contextClass, contentType)) {
@@ -195,17 +195,17 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 				}
 				if (converterTypeToUse != null) {
 					if (message.hasBody()) {
-						HttpInputMessage msgToUse =
-								getAdvice().beforeBodyRead(message, parameter, targetType, converterClass);
+						HttpInputMessage msgToUse = this.advice.beforeBodyRead(message, parameter, targetType, converterClass);
 						body = switch (converterTypeToUse) {
 							case BASE -> ((HttpMessageConverter<T>) converter).read(targetClass, msgToUse);
 							case GENERIC -> ((GenericHttpMessageConverter<?>) converter).read(targetType, contextClass, msgToUse);
-							case SMART -> ((SmartHttpMessageConverter<?>) converter).read(targetResolvableType, msgToUse, null);
+							case SMART -> ((SmartHttpMessageConverter<?>) converter).read(targetResolvableType, msgToUse,
+									this.advice.determineReadHints(parameter, targetType, (Class<SmartHttpMessageConverter<?>>) converterClass));
 						};
-						body = getAdvice().afterBodyRead(body, msgToUse, parameter, targetType, converterClass);
+						body = this.advice.afterBodyRead(body, msgToUse, parameter, targetType, converterClass);
 					}
 					else {
-						body = getAdvice().handleEmptyBody(null, message, parameter, targetType, converterClass);
+						body = this.advice.handleEmptyBody(null, message, parameter, targetType, converterClass);
 					}
 					break;
 				}
@@ -213,7 +213,7 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 			}
 
 			if (body == NO_VALUE && noContentType && !message.hasBody()) {
-				body = getAdvice().handleEmptyBody(
+				body = this.advice.handleEmptyBody(
 						null, message, parameter, targetType, NoContentTypeHttpMessageConverter.class);
 			}
 		}

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -324,7 +324,7 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 					}
 				}
 				else if (converter instanceof SmartHttpMessageConverter smartConverter) {
-					targetResolvableType = getNestedTypeIfNeeded(ResolvableType.forMethodParameter(returnType));
+					targetResolvableType = getNestedTypeIfNeeded(ResolvableType.forType(targetType));
 					if (smartConverter.canWrite(targetResolvableType, valueType, selectedMediaType)) {
 						converterTypeToUse = ConverterType.SMART;
 					}
@@ -343,7 +343,9 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 						switch (converterTypeToUse) {
 							case BASE -> converter.write(body, selectedMediaType, outputMessage);
 							case GENERIC -> ((GenericHttpMessageConverter) converter).write(body, targetType, selectedMediaType, outputMessage);
-							case SMART -> ((SmartHttpMessageConverter) converter).write(body, targetResolvableType, selectedMediaType, outputMessage, null);
+							case SMART -> ((SmartHttpMessageConverter) converter).write(body, targetResolvableType,
+									selectedMediaType, outputMessage, getAdvice().determineWriteHints(body, returnType,
+											selectedMediaType, (Class<? extends HttpMessageConverter<?>>) converter.getClass()));
 						}
 					}
 					else {

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/JsonViewRequestBodyAdvice.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -18,12 +18,17 @@ package org.springframework.web.servlet.mvc.method.annotation;
 
 import java.io.IOException;
 import java.lang.reflect.Type;
+import java.util.Collections;
+import java.util.Map;
 
 import com.fasterxml.jackson.annotation.JsonView;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.http.HttpInputMessage;
+import org.springframework.http.converter.AbstractJacksonHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.SmartHttpMessageConverter;
 import org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter;
 import org.springframework.http.converter.json.MappingJacksonInputMessage;
 import org.springframework.util.Assert;
@@ -52,14 +57,28 @@ public class JsonViewRequestBodyAdvice extends RequestBodyAdviceAdapter {
 	public boolean supports(MethodParameter methodParameter, Type targetType,
 			Class<? extends HttpMessageConverter<?>> converterType) {
 
-		return (AbstractJackson2HttpMessageConverter.class.isAssignableFrom(converterType) &&
-				methodParameter.getParameterAnnotation(JsonView.class) != null);
+		return methodParameter.getParameterAnnotation(JsonView.class) != null &&
+				(AbstractJacksonHttpMessageConverter.class.isAssignableFrom(converterType) ||
+						AbstractJackson2HttpMessageConverter.class.isAssignableFrom(converterType));
 	}
 
 	@Override
 	public HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter methodParameter,
 			Type targetType, Class<? extends HttpMessageConverter<?>> selectedConverterType) throws IOException {
 
+		if (AbstractJacksonHttpMessageConverter.class.isAssignableFrom(selectedConverterType)) {
+			return inputMessage;
+		}
+
+		return new MappingJacksonInputMessage(inputMessage.getBody(), inputMessage.getHeaders(), getJsonView(methodParameter));
+	}
+
+	@Override
+	public @Nullable Map<String, Object> determineReadHints(MethodParameter parameter, Type targetType, Class<? extends SmartHttpMessageConverter<?>> converterType) {
+		return Collections.singletonMap(JsonView.class.getName(), getJsonView(parameter));
+	}
+
+	private static Class<?> getJsonView(MethodParameter methodParameter) {
 		JsonView ann = methodParameter.getParameterAnnotation(JsonView.class);
 		Assert.state(ann != null, "No JsonView annotation");
 
@@ -68,8 +87,6 @@ public class JsonViewRequestBodyAdvice extends RequestBodyAdviceAdapter {
 			throw new IllegalArgumentException(
 					"@JsonView only supported for request body advice with exactly 1 class argument: " + methodParameter);
 		}
-
-		return new MappingJacksonInputMessage(inputMessage.getBody(), inputMessage.getHeaders(), classes[0]);
+		return classes[0];
 	}
-
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/JsonViewResponseBodyAdvice.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -16,7 +16,11 @@
 
 package org.springframework.web.servlet.mvc.method.annotation;
 
+import java.util.Collections;
+import java.util.Map;
+
 import com.fasterxml.jackson.annotation.JsonView;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.http.MediaType;
@@ -55,6 +59,15 @@ public class JsonViewResponseBodyAdvice extends AbstractMappingJacksonResponseBo
 	protected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer, MediaType contentType,
 			MethodParameter returnType, ServerHttpRequest request, ServerHttpResponse response) {
 
+		bodyContainer.setSerializationView(getJsonView(returnType));
+	}
+
+	@Override
+	public @Nullable Map<String, Object> determineWriteHints(@Nullable Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType) {
+		return Collections.singletonMap(JsonView.class.getName(), getJsonView(returnType));
+	}
+
+	private static Class<?> getJsonView(MethodParameter returnType) {
 		JsonView ann = returnType.getMethodAnnotation(JsonView.class);
 		Assert.state(ann != null, "No JsonView annotation");
 
@@ -63,8 +76,6 @@ public class JsonViewResponseBodyAdvice extends AbstractMappingJacksonResponseBo
 			throw new IllegalArgumentException(
 					"@JsonView only supported for response body advice with exactly 1 class argument: " + returnType);
 		}
-
-		bodyContainer.setSerializationView(classes[0]);
+		return classes[0];
 	}
-
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestBodyAdvice.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -18,12 +18,14 @@ package org.springframework.web.servlet.mvc.method.annotation;
 
 import java.io.IOException;
 import java.lang.reflect.Type;
+import java.util.Map;
 
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.SmartHttpMessageConverter;
 
 /**
  * Allows customizing the request before its body is read and converted into an
@@ -36,6 +38,7 @@ import org.springframework.http.converter.HttpMessageConverter;
  * {@code @ControllerAdvice} in which case they are auto-detected.
  *
  * @author Rossen Stoyanchev
+ * @author Sebastien Deleuze
  * @since 4.2
  */
 public interface RequestBodyAdvice {
@@ -63,6 +66,20 @@ public interface RequestBodyAdvice {
 	HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter,
 			Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException;
 
+	/**
+	 * Invoked to determine read hints if the converter is a {@link SmartHttpMessageConverter}.
+	 * @param parameter the target method parameter
+	 * @param targetType the target type, not necessarily the same as the method
+	 * parameter type, for example, for {@code HttpEntity<String>}.
+	 * @param converterType the selected converter type
+	 * @return the hints determined otherwise {@code null}
+	 * @since 7.0
+	 */
+	default @Nullable Map<String, Object> determineReadHints(MethodParameter parameter,
+			Type targetType, Class<? extends SmartHttpMessageConverter<?>> converterType) {
+		return null;
+	}
+
 	/**
 	 * Invoked third (and last) after the request body is converted to an Object.
 	 * @param body set to the converter Object before the first advice is called
@@ -90,5 +107,4 @@ public interface RequestBodyAdvice {
 	@Nullable Object handleEmptyBody(@Nullable Object body, HttpInputMessage inputMessage, MethodParameter parameter,
 			Type targetType, Class<? extends HttpMessageConverter<?>> converterType);
 
-
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyAdviceChain.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -20,7 +20,9 @@ import java.io.IOException;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 import org.jspecify.annotations.Nullable;
 
@@ -28,6 +30,7 @@ import org.springframework.core.MethodParameter;
 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.SmartHttpMessageConverter;
 import org.springframework.http.server.ServerHttpRequest;
 import org.springframework.http.server.ServerHttpResponse;
 import org.springframework.util.CollectionUtils;
@@ -36,7 +39,7 @@ import org.springframework.web.method.ControllerAdviceBean;
 /**
  * Invokes {@link RequestBodyAdvice} and {@link ResponseBodyAdvice} where each
  * instance may be (and is most likely) wrapped with
- * {@link org.springframework.web.method.ControllerAdviceBean ControllerAdviceBean}.
+ * {@link ControllerAdviceBean ControllerAdviceBean}.
  *
  * @author Rossen Stoyanchev
  * @since 4.2
@@ -176,4 +179,38 @@ class RequestResponseBodyAdviceChain implements RequestBodyAdvice, ResponseBodyA
 		}
 	}
 
+	@Override
+	public @Nullable Map<String, Object> determineReadHints(MethodParameter parameter, Type targetType, Class<? extends SmartHttpMessageConverter<?>> converterType) {
+		Map<String, Object> hints = null;
+		for (RequestBodyAdvice advice : getMatchingAdvice(parameter, RequestBodyAdvice.class)) {
+			if (advice.supports(parameter, targetType, converterType)) {
+				Map<String, Object> adviceHints = advice.determineReadHints(parameter, targetType, converterType);
+				if (adviceHints != null) {
+					if (hints == null) {
+						hints = new HashMap<>(adviceHints.size());
+					}
+					hints.putAll(adviceHints);
+				}
+			}
+		}
+		return hints;
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public @Nullable Map<String, Object> determineWriteHints(@Nullable Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType) {
+		Map<String, Object> hints = null;
+		for (ResponseBodyAdvice<?> advice : getMatchingAdvice(returnType, ResponseBodyAdvice.class)) {
+			if (advice.supports(returnType, selectedConverterType)) {
+				Map<String, Object> adviceHints = ((ResponseBodyAdvice<Object>) advice).determineWriteHints(body, returnType, selectedContentType, selectedConverterType);
+				if (adviceHints != null) {
+					if (hints == null) {
+						hints = new HashMap<>(adviceHints.size());
+					}
+					hints.putAll(adviceHints);
+				}
+			}
+		}
+		return hints;
+	}
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyAdvice.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -16,11 +16,14 @@
 
 package org.springframework.web.servlet.mvc.method.annotation;
 
+import java.util.Map;
+
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.SmartHttpMessageConverter;
 import org.springframework.http.server.ServerHttpRequest;
 import org.springframework.http.server.ServerHttpResponse;
 
@@ -35,6 +38,7 @@ import org.springframework.http.server.ServerHttpResponse;
  * will be auto-detected by both.
  *
  * @author Rossen Stoyanchev
+ * @author Sebastien Deleuze
  * @since 4.1
  * @param <T> the body type
  */
@@ -65,4 +69,18 @@ public interface ResponseBodyAdvice<T> {
 			Class<? extends HttpMessageConverter<?>> selectedConverterType,
 			ServerHttpRequest request, ServerHttpResponse response);
 
+	/**
+	 * Invoked to determine write hints if the converter is a {@link SmartHttpMessageConverter}.
+	 * @param body the body to be written
+	 * @param returnType the return type of the controller method
+	 * @param selectedContentType the content type selected through content negotiation
+	 * @param selectedConverterType the converter type selected to write to the response
+	 * @return the hints determined otherwise {@code null}
+	 * @since 7.0
+	 */
+	default @Nullable Map<String, Object> determineWriteHints(@Nullable T body, MethodParameter returnType, MediaType selectedContentType,
+			Class<? extends HttpMessageConverter<?>> selectedConverterType) {
+		return null;
+	}
+
 }

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyAdviceChainTests.java

@@ -17,10 +17,14 @@
 package org.springframework.web.servlet.mvc.method.annotation;
 
 import java.io.IOException;
+import java.lang.reflect.Type;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
+import java.util.Objects;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.context.support.StaticApplicationContext;
@@ -29,7 +33,9 @@ import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.SmartHttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
+import org.springframework.http.converter.json.JacksonJsonHttpMessageConverter;
 import org.springframework.http.server.ServerHttpRequest;
 import org.springframework.http.server.ServerHttpResponse;
 import org.springframework.http.server.ServletServerHttpRequest;
@@ -52,6 +58,7 @@ import static org.mockito.Mockito.mock;
  * Tests for {@link RequestResponseBodyAdviceChain}.
  *
  * @author Rossen Stoyanchev
+ * @author Sebastien Deleuze
  * @since 4.2
  */
 class RequestResponseBodyAdviceChainTests {
@@ -131,6 +138,20 @@ class RequestResponseBodyAdviceChainTests {
 		assertThat(actual).isEqualTo(this.body);
 	}
 
+	@Test
+	void controllerAdviceWithHints() {
+		Object fooAdviceBean = createControllerAdviceBean(FooHintControllerAdvice.class);
+		Object barAdviceBean = createControllerAdviceBean(BarHintControllerAdvice.class);
+		RequestResponseBodyAdviceChain chain = new RequestResponseBodyAdviceChain(List.of(fooAdviceBean, barAdviceBean));
+
+		Map<String, Object> readHints = chain.determineReadHints(this.paramType, this.paramType.getGenericParameterType(),
+				JacksonJsonHttpMessageConverter.class);
+		assertThat(readHints).containsExactlyInAnyOrderEntriesOf(Map.of("foo", "String", "bar", "String"));
+
+		Map<String, Object> writeHints = chain.determineWriteHints(this.body, this.returnType, this.contentType, this.converterType);
+		assertThat(writeHints).containsExactlyInAnyOrderEntriesOf(Map.of("foo", "body", "bar", "body"));
+	}
+
 	private ControllerAdviceBean createControllerAdviceBean(Class<?> beanType) {
 		StaticApplicationContext applicationContext = new StaticApplicationContext();
 		applicationContext.registerSingleton(beanType.getSimpleName(), beanType);
@@ -174,6 +195,64 @@ class RequestResponseBodyAdviceChainTests {
 		}
 	}
 
+	@ControllerAdvice
+	private static class FooHintControllerAdvice extends RequestBodyAdviceAdapter implements ResponseBodyAdvice<String> {
+
+		@Override
+		public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
+			return true;
+		}
+
+		@Override
+		public @Nullable String beforeBodyWrite(@Nullable String body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
+			return body;
+		}
+
+		@Override
+		public @Nullable Map<String, Object> determineWriteHints(@Nullable String body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType) {
+			return Collections.singletonMap("foo", Objects.requireNonNull(body));
+		}
+
+		@Override
+		public boolean supports(MethodParameter methodParameter, Type targetType, Class<? extends HttpMessageConverter<?>> converterType) {
+			return true;
+		}
+
+		@Override
+		public @Nullable Map<String, Object> determineReadHints(MethodParameter parameter, Type targetType, Class<? extends SmartHttpMessageConverter<?>> converterType) {
+			return Collections.singletonMap("foo", parameter.getParameterType().getSimpleName());
+		}
+
+	}
+
+	@ControllerAdvice
+	private static class BarHintControllerAdvice extends RequestBodyAdviceAdapter implements ResponseBodyAdvice<String> {
+		@Override
+		public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
+			return true;
+		}
+
+		@Override
+		public @Nullable String beforeBodyWrite(@Nullable String body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
+			return body;
+		}
+
+		@Override
+		public @Nullable Map<String, Object> determineWriteHints(@Nullable String body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType) {
+			return Collections.singletonMap("bar", Objects.requireNonNull(body));
+		}
+
+		@Override
+		public boolean supports(MethodParameter methodParameter, Type targetType, Class<? extends HttpMessageConverter<?>> converterType) {
+			return true;
+		}
+
+		@Override
+		public @Nullable Map<String, Object> determineReadHints(MethodParameter parameter, Type targetType, Class<? extends SmartHttpMessageConverter<?>> converterType) {
+			return Collections.singletonMap("bar", parameter.getParameterType().getSimpleName());
+		}
+	}
+
 
 	@SuppressWarnings("unused")
 	@ResponseBody