Merge branch '2.4.x' into 2.5.x

Closes gh-27361

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/HttpMessageConverters.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -20,8 +20,10 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Map;
 
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
@@ -63,6 +65,15 @@ public class HttpMessageConverters implements Iterable<HttpMessageConverter<?>>
 		NON_REPLACING_CONVERTERS = Collections.unmodifiableList(nonReplacingConverters);
 	}
 
+	private static final Map<Class<?>, Class<?>> EQUIVALENT_CONVERTERS;
+
+	static {
+		Map<Class<?>, Class<?>> equivalentConverters = new HashMap<>();
+		putIfExists(equivalentConverters, "org.springframework.http.converter.json.MappingJackson2HttpMessageConverter",
+				"org.springframework.http.converter.json.GsonHttpMessageConverter");
+		EQUIVALENT_CONVERTERS = Collections.unmodifiableMap(equivalentConverters);
+	}
+
 	private final List<HttpMessageConverter<?>> converters;
 
 	/**
@@ -132,7 +143,12 @@ public class HttpMessageConverters implements Iterable<HttpMessageConverter<?>>
 				return false;
 			}
 		}
-		return ClassUtils.isAssignableValue(defaultConverter.getClass(), candidate);
+		Class<?> converterClass = defaultConverter.getClass();
+		if (ClassUtils.isAssignableValue(converterClass, candidate)) {
+			return true;
+		}
+		Class<?> equivalentClass = EQUIVALENT_CONVERTERS.get(converterClass);
+		return equivalentClass != null && ClassUtils.isAssignableValue(equivalentClass, candidate);
 	}
 
 	private void configurePartConverters(AllEncompassingFormHttpMessageConverter formConverter,
@@ -220,4 +236,13 @@ public class HttpMessageConverters implements Iterable<HttpMessageConverter<?>>
 		}
 	}
 
+	private static void putIfExists(Map<Class<?>, Class<?>> map, String keyClassName, String valueClassName) {
+		try {
+			map.put(Class.forName(keyClassName), Class.forName(valueClassName));
+		}
+		catch (ClassNotFoundException | NoClassDefFoundError ex) {
+			// Ignore
+		}
+	}
+
 }

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersTests.java

@@ -19,6 +19,7 @@ package org.springframework.boot.autoconfigure.http;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.junit.jupiter.api.Test;
 
@@ -28,6 +29,7 @@ import org.springframework.http.converter.ResourceHttpMessageConverter;
 import org.springframework.http.converter.ResourceRegionHttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.cbor.MappingJackson2CborHttpMessageConverter;
+import org.springframework.http.converter.json.GsonHttpMessageConverter;
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.http.converter.smile.MappingJackson2SmileHttpMessageConverter;
 import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
@@ -80,6 +82,16 @@ class HttpMessageConvertersTests {
 		assertThat(converters.getConverters().indexOf(converter1)).isNotEqualTo(0);
 	}
 
+	@Test
+	void addBeforeExistingEquivalentConverter() {
+		GsonHttpMessageConverter converter1 = new GsonHttpMessageConverter();
+		HttpMessageConverters converters = new HttpMessageConverters(converter1);
+		List<Class<?>> converterClasses = converters.getConverters().stream().map(HttpMessageConverter::getClass)
+				.collect(Collectors.toList());
+		assertThat(converterClasses).containsSequence(GsonHttpMessageConverter.class,
+				MappingJackson2HttpMessageConverter.class);
+	}
+
 	@Test
 	void addNewConverters() {
 		HttpMessageConverter<?> converter1 = mock(HttpMessageConverter.class);