Merge branch '3.1.x'

Closes gh-37942

Author: wilkinsona

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/CollectionBinder.java

@@ -40,12 +40,11 @@ class CollectionBinder extends IndexedElementsBinder<Collection<Object>> {
 	@Override
 	protected Object bindAggregate(ConfigurationPropertyName name, Bindable<?> target,
 			AggregateElementBinder elementBinder) {
-		Class<?> collectionType = (target.getValue() != null) ? List.class : target.getType().resolve(Object.class);
 		ResolvableType aggregateType = ResolvableType.forClassWithGenerics(List.class,
 				target.getType().asCollection().getGenerics());
 		ResolvableType elementType = target.getType().asCollection().getGeneric();
 		IndexedCollectionSupplier result = new IndexedCollectionSupplier(
-				() -> CollectionFactory.createCollection(collectionType, elementType.resolve(), 0));
+				() -> CollectionFactory.createCollection(List.class, elementType.resolve(), 0));
 		bindIndexed(name, target, elementBinder, aggregateType, elementType, result);
 		if (result.wasSupplied()) {
 			return result.get();

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/ConfigurationPropertiesTests.java

@@ -1190,6 +1190,19 @@ void loadWhenBindingClasspathPatternToResourceCollectionShouldBindMultipleValues
 		assertThat(properties.getResources()).hasSizeGreaterThan(1);
 	}
 
+	@Test
+	void loadWhenBindingToConstructorParametersWithConversionToCustomListImplementation() {
+		load(ConstructorBoundCustomListPropertiesConfiguration.class, "test.values=a,b");
+		assertThat(this.context.getBean(ConstructorBoundCustomListProperties.class).getValues()).containsExactly("a",
+				"b");
+	}
+
+	@Test
+	void loadWhenBindingToJavaBeanWithConversionToCustomListImplementation() {
+		load(SetterBoundCustomListPropertiesConfiguration.class, "test.values=a,b");
+		assertThat(this.context.getBean(SetterBoundCustomListProperties.class).getValues()).containsExactly("a", "b");
+	}
+
 	private AnnotationConfigApplicationContext load(Class<?> configuration, String... inlinedProperties) {
 		return load(new Class<?>[] { configuration }, inlinedProperties);
 	}
@@ -3115,4 +3128,80 @@ void setResources(Collection<Resource> resources) {
 
 	}
 
+	@EnableConfigurationProperties(ConstructorBoundCustomListProperties.class)
+	static class ConstructorBoundCustomListPropertiesConfiguration {
+
+		@Bean
+		@ConfigurationPropertiesBinding
+		static Converter<ArrayList<?>, CustomList<?>> arrayListToCustomList() {
+			return new Converter<>() {
+
+				@Override
+				public CustomList<?> convert(ArrayList<?> source) {
+					return new CustomList<>(source);
+				}
+
+			};
+
+		}
+
+	}
+
+	@ConfigurationProperties("test")
+	static class ConstructorBoundCustomListProperties {
+
+		private final CustomList<String> values;
+
+		ConstructorBoundCustomListProperties(CustomList<String> values) {
+			this.values = values;
+		}
+
+		CustomList<String> getValues() {
+			return this.values;
+		}
+
+	}
+
+	@EnableConfigurationProperties(SetterBoundCustomListProperties.class)
+	static class SetterBoundCustomListPropertiesConfiguration {
+
+		@Bean
+		@ConfigurationPropertiesBinding
+		static Converter<ArrayList<?>, CustomList<?>> arrayListToCustomList() {
+			return new Converter<>() {
+
+				@Override
+				public CustomList<?> convert(ArrayList<?> source) {
+					return new CustomList<>(source);
+				}
+
+			};
+
+		}
+
+	}
+
+	@ConfigurationProperties("test")
+	static class SetterBoundCustomListProperties {
+
+		private CustomList<String> values;
+
+		CustomList<String> getValues() {
+			return this.values;
+		}
+
+		void setValues(CustomList<String> values) {
+			this.values = values;
+		}
+
+	}
+
+	static final class CustomList<E> extends ArrayList<E> {
+
+		CustomList(List<E> delegate) {
+			super(delegate);
+		}
+
+	}
+
 }