Media types by Class for HttpMessageConverter

See gh-26212

spring-web/src/main/java/org/springframework/http/converter/HttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -17,6 +17,7 @@
 package org.springframework.http.converter;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.List;
 
 import org.springframework.http.HttpInputMessage;
@@ -53,11 +54,30 @@ public interface HttpMessageConverter<T> {
 	boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType);
 
 	/**
-	 * Return the list of {@link MediaType} objects supported by this converter.
-	 * @return the list of supported media types, potentially an immutable copy
+	 * Return the list of media types supported by this converter. The list may
+	 * not apply to every possible target element type and calls to this method
+	 * should typically be guarded via {@link #canWrite(Class, MediaType)
+	 * canWrite(clazz, null}. The list may also exclude MIME types supported
+	 * only for a specific class. Alternatively, use
+	 * {@link #getSupportedMediaTypes(Class)} for a more precise list.
+	 * @return the list of supported media types
 	 */
 	List<MediaType> getSupportedMediaTypes();
 
+	/**
+	 * Return the list of media types supported by this converter for the given
+	 * class. The list may differ from {@link #getSupportedMediaTypes()} if the
+	 * converter doesn't support given Class or if it support it only for a
+	 * subset of media types.
+	 * @param clazz the type of class to check
+	 * @return the list of media types supported for the given class
+	 * @since 5.3.4
+	 */
+	default List<MediaType> getSupportedMediaTypes(Class<?> clazz) {
+		return (canRead(clazz, null) || canWrite(clazz, null) ?
+				getSupportedMediaTypes() : Collections.emptyList());
+	}
+
 	/**
 	 * Read an object of the given type from the given input message, and returns it.
 	 * @param clazz the type of object to return. This type must have previously been passed to the

spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java

@@ -23,6 +23,7 @@ import java.io.Reader;
 import java.lang.reflect.Type;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
@@ -194,6 +195,18 @@ public abstract class AbstractJackson2HttpMessageConverter extends AbstractGener
 		return Collections.emptyMap();
 	}
 
+	@Override
+	public List<MediaType> getSupportedMediaTypes(Class<?> clazz) {
+		List<MediaType> result = null;
+		for (Map.Entry<Class<?>, Map<MediaType, ObjectMapper>> entry : getObjectMapperRegistrations().entrySet()) {
+			if (entry.getKey().isAssignableFrom(clazz)) {
+				result = (result != null ? result : new ArrayList<>(entry.getValue().size()));
+				result.addAll(entry.getValue().keySet());
+			}
+		}
+		return (CollectionUtils.isEmpty(result) ? getSupportedMediaTypes() : result);
+	}
+
 	private Map<Class<?>, Map<MediaType, ObjectMapper>> getObjectMapperRegistrations() {
 		return (this.objectMapperRegistrations != null ? this.objectMapperRegistrations : Collections.emptyMap());
 	}

spring-web/src/main/java/org/springframework/web/client/RestTemplate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -17,6 +17,7 @@
 package org.springframework.web.client;
 
 import java.io.IOException;
+import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.net.URI;
 import java.util.ArrayList;
@@ -885,7 +886,7 @@ public class RestTemplate extends InterceptingHttpAccessor implements RestOperat
 			if (this.responseType != null) {
 				List<MediaType> allSupportedMediaTypes = getMessageConverters().stream()
 						.filter(converter -> canReadResponse(this.responseType, converter))
-						.flatMap(this::getSupportedMediaTypes)
+						.flatMap((HttpMessageConverter<?> converter) -> getSupportedMediaTypes(this.responseType, converter))
 						.distinct()
 						.sorted(MediaType.SPECIFICITY_COMPARATOR)
 						.collect(Collectors.toList());
@@ -908,8 +909,10 @@ public class RestTemplate extends InterceptingHttpAccessor implements RestOperat
 			return false;
 		}
 
-		private Stream<MediaType> getSupportedMediaTypes(HttpMessageConverter<?> messageConverter) {
-			return messageConverter.getSupportedMediaTypes()
+		private Stream<MediaType> getSupportedMediaTypes(Type type, HttpMessageConverter<?> converter) {
+			Type rawType = (type instanceof ParameterizedType ? ((ParameterizedType) type).getRawType() : type);
+			Class<?> clazz = (rawType instanceof Class ? (Class<?>) rawType : null);
+			return (clazz != null ? converter.getSupportedMediaTypes(clazz) : converter.getSupportedMediaTypes())
 					.stream()
 					.map(mediaType -> {
 						if (mediaType.getCharset() != null) {