Back-off in ResultProcessor if the result object is an instance of the target type.

We now do not attempt to convert the object if it is an instance of the declared target type.

Closes #2347.

Author: mp911de

src/main/java/org/springframework/data/repository/query/ResultProcessor.java

@@ -219,6 +219,10 @@ public ChainingConverter and(final Converter<Object, Object> converter) {
 
 			return new ChainingConverter(targetType, source -> {
 
+				if (source == null || targetType.isInstance(source)) {
+					return source;
+				}
+
 				Object intermediate = ChainingConverter.this.convert(source);
 
 				return intermediate == null || targetType.isInstance(intermediate) ? intermediate

src/test/java/org/springframework/data/repository/query/ResultProcessorUnitTests.java

@@ -19,8 +19,10 @@
 import static org.mockito.Mockito.*;
 
 import io.reactivex.Flowable;
+import lombok.Getter;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
 import rx.Observable;
 import rx.Single;
 
@@ -308,6 +310,37 @@ void supportsFlowableProjections() throws Exception {
 		assertThat(content.get(0)).isInstanceOf(SampleProjection.class);
 	}
 
+	@Test // GH-2347
+	void findByListSkipsConversionIfTypeAlreadyMatches() throws Exception {
+
+		List<AbstractDto> result = getProcessor("findAllAbstractDtos")
+				.processResult(Collections.singletonList(new ConcreteDto("Walter", "White")));
+
+		assertThat(result.get(0)).isInstanceOf(ConcreteDto.class);
+	}
+
+	@Test // GH-2347
+	void streamBySkipsConversionIfTypeAlreadyMatches() throws Exception {
+
+		Stream<AbstractDto> result = getProcessor("streamAllAbstractDtos")
+				.processResult(Stream.of(new ConcreteDto("Walter", "White")));
+
+		assertThat(result.findFirst().get()).isInstanceOf(ConcreteDto.class);
+	}
+
+	@Test // GH-2347
+	void findFluxSkipsConversionIfTypeAlreadyMatches() throws Exception {
+
+		Flux<AbstractDto> result = getProcessor("findFluxOfAbstractDtos")
+				.processResult(Flux.just(new ConcreteDto("Walter", "White")));
+
+		result.as(StepVerifier::create) //
+				.consumeNextWith(actual -> {
+
+					assertThat(actual).isInstanceOf(ConcreteDto.class);
+				}).verifyComplete();
+	}
+
 	private static ResultProcessor getProcessor(String methodName, Class<?>... parameters) throws Exception {
 		return getQueryMethod(methodName, parameters).getResultProcessor();
 	}
@@ -356,6 +389,12 @@ interface SampleRepository extends Repository<Sample, Long> {
 		Observable<SampleProjection> findObservableProjection();
 
 		Flowable<SampleProjection> findFlowableProjection();
+
+		List<AbstractDto> findAllAbstractDtos();
+
+		Stream<AbstractDto> streamAllAbstractDtos();
+
+		Flux<AbstractDto> findFluxOfAbstractDtos();
 	}
 
 	static class Sample {
@@ -367,6 +406,23 @@ public Sample(String firstname, String lastname) {
 		}
 	}
 
+	@Getter
+	static abstract class AbstractDto {
+		final String firstname, lastname;
+
+		public AbstractDto(String firstname, String lastname) {
+			this.firstname = firstname;
+			this.lastname = lastname;
+		}
+	}
+
+	static class ConcreteDto extends AbstractDto {
+
+		public ConcreteDto(String firstname, String lastname) {
+			super(firstname, lastname);
+		}
+	}
+
 	static class SampleDto {}
 
 	@lombok.Value