Add fallback to pre-6.2.3 behavior for unresolvable generics

Closes gh-34535

Author: jhoeller

spring-core/src/main/java/org/springframework/core/convert/support/GenericConversionService.java

@@ -348,6 +348,13 @@ public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
 					conditionalConverter.matches(sourceType, targetType);
 		}
 
+		public boolean matchesFallback(TypeDescriptor sourceType, TypeDescriptor targetType) {
+			return (this.typeInfo.getTargetType() == targetType.getObjectType() &&
+					this.targetType.hasUnresolvableGenerics() &&
+					(!(this.converter instanceof ConditionalConverter conditionalConverter) ||
+							conditionalConverter.matches(sourceType, targetType)));
+		}
+
 		@Override
 		@Nullable
 		public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
@@ -622,12 +629,20 @@ public void add(GenericConverter converter) {
 
 		@Nullable
 		public GenericConverter getConverter(TypeDescriptor sourceType, TypeDescriptor targetType) {
+			// Look for proper match among all converters (taking full generics into account)
 			for (GenericConverter converter : this.converters) {
 				if (!(converter instanceof ConditionalGenericConverter genericConverter) ||
 						genericConverter.matches(sourceType, targetType)) {
 					return converter;
 				}
 			}
+			// Fallback to pre-6.2.3 behavior: accept Class match for unresolvable generics
+			for (GenericConverter converter : this.converters) {
+				if (converter instanceof ConverterAdapter converterAdapter &&
+						converterAdapter.matchesFallback(sourceType, targetType)) {
+					return converter;
+				}
+			}
 			return null;
 		}
 

spring-core/src/test/java/org/springframework/core/convert/support/GenericConversionServiceTests.java

@@ -581,6 +581,18 @@ void stringListToListOfSubclassOfUnboundGenericClass() {
 		assertThat(bList).allMatch(e -> e instanceof BRaw);
 	}
 
+	@Test
+	void stringToListOfMapConverterWithFallbackMatch() {
+		conversionService.addConverter(new StringToListOfMapConverter());
+
+		List<Map<String, Object>> result = (List<Map<String, Object>>) conversionService.convert("foo",
+				TypeDescriptor.valueOf(String.class),
+				TypeDescriptor.collection(List.class, TypeDescriptor.valueOf(Map.class))
+		);
+
+		assertThat("foo").isEqualTo(result.get(0).get("bar"));
+	}
+
 
 	@ExampleAnnotation(active = true)
 	public String annotatedString;
@@ -971,4 +983,13 @@ public List<BRaw> convert(List<String> source) {
 		}
 	}
 
+
+	private static class StringToListOfMapConverter implements Converter<String, List<? extends Map<String, ?>>> {
+
+		@Override
+		public List<? extends Map<String, ?>> convert(String source) {
+			return List.of(Map.of("bar", source));
+		}
+	}
+
 }