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.

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

@@ -219,6 +219,10 @@ public class ResultProcessor {
 
 			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.assertj.core.api.Assertions.*;
 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 @@ class ResultProcessorUnitTests {
 		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 @@ class ResultProcessorUnitTests {
 		Observable<SampleProjection> findObservableProjection();
 
 		Flowable<SampleProjection> findFlowableProjection();
+
+		List<AbstractDto> findAllAbstractDtos();
+
+		Stream<AbstractDto> streamAllAbstractDtos();
+
+		Flux<AbstractDto> findFluxOfAbstractDtos();
 	}
 
 	static class Sample {
@@ -367,6 +406,23 @@ class ResultProcessorUnitTests {
 		}
 	}
 
+	@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