Ensure conversion service actually converts to the correct type

Update `BindConverter` with a guard to ensure that the resulting object
is the correct type.

Fixes gh-28592

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -106,7 +106,10 @@ final class BindConverter {
 		for (ConversionService delegate : this.delegates) {
 			try {
 				if (delegate.canConvert(sourceType, targetType)) {
-					return delegate.convert(source, sourceType, targetType);
+					Object converted = delegate.convert(source, sourceType, targetType);
+					if (targetType.getType().isInstance(converted)) {
+						return converted;
+					}
 				}
 			}
 			catch (ConversionException ex) {

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

@@ -57,6 +57,7 @@ import org.springframework.boot.context.properties.bind.BindException;
 import org.springframework.boot.context.properties.bind.DefaultValue;
 import org.springframework.boot.context.properties.bind.validation.BindValidationException;
 import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
+import org.springframework.boot.convert.ApplicationConversionService;
 import org.springframework.boot.convert.DataSizeUnit;
 import org.springframework.boot.convert.DurationFormat;
 import org.springframework.boot.convert.DurationStyle;
@@ -1081,6 +1082,15 @@ class ConfigurationPropertiesTests {
 		assertThat(keys.stream().map(ConfigurationPropertyName::toString)).contains("name", "nested.name");
 	}
 
+	@Test // gh-28592
+	void loadWhenBindingWithCustomConverterAndObjectToObjectMethod() {
+		this.context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance());
+		load(WithCustomConverterAndObjectToObjectMethodConfiguration.class, "test.item=foo");
+		WithCustomConverterAndObjectToObjectMethodProperties bean = this.context
+				.getBean(WithCustomConverterAndObjectToObjectMethodProperties.class);
+		assertThat(bean.getItem().getValue()).isEqualTo("foo");
+	}
+
 	private AnnotationConfigApplicationContext load(Class<?> configuration, String... inlinedProperties) {
 		return load(new Class<?>[] { configuration }, inlinedProperties);
 	}
@@ -2710,4 +2720,40 @@ class ConfigurationPropertiesTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	@EnableConfigurationProperties(WithCustomConverterAndObjectToObjectMethodProperties.class)
+	static class WithCustomConverterAndObjectToObjectMethodConfiguration {
+
+		@Bean
+		@ConfigurationPropertiesBinding
+		WithObjectToObjectMethodConverter withObjectToObjectMethodConverter() {
+			return new WithObjectToObjectMethodConverter();
+		}
+
+	}
+
+	@ConfigurationProperties("test")
+	static class WithCustomConverterAndObjectToObjectMethodProperties {
+
+		private WithPublicObjectToObjectMethod item;
+
+		WithPublicObjectToObjectMethod getItem() {
+			return this.item;
+		}
+
+		void setItem(WithPublicObjectToObjectMethod item) {
+			this.item = item;
+		}
+
+	}
+
+	static class WithObjectToObjectMethodConverter implements Converter<String, WithPublicObjectToObjectMethod> {
+
+		@Override
+		public WithPublicObjectToObjectMethod convert(String source) {
+			return new WithPublicObjectToObjectMethod(source);
+		}
+
+	}
+
 }

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

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2012-2022 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.context.properties;
+
+import java.util.Optional;
+
+/**
+ * Data object with a pubic method picked up by the {@code ObjectToObjectConverter}. Used
+ * in {@link ConfigurationPropertiesTests}.
+ *
+ * @author Phillip Webb
+ */
+public class WithPublicObjectToObjectMethod {
+
+	private final String value;
+
+	WithPublicObjectToObjectMethod(String value) {
+		this.value = value;
+	}
+
+	String getValue() {
+		return this.value;
+	}
+
+	public static Optional<WithPublicObjectToObjectMethod> from(String value) {
+		return Optional.of(new WithPublicObjectToObjectMethod(value));
+	}
+
+}