DATACMNS-859, DATACMNS-860 - Improvements to ResourceProcessor.

ResourceProcessor supports Streams now and adds a map(…) step to apply projections.

Also, the ProjectingConverter falls back to use a default ConversionService instance to make use of the object mapping functionality implemented in ObjectToObjectConverter, i.e. the ability to just map an object returned from the store to a DTO in case that latter exposes a constructor or factory methods taking the source instance as parameter.

Related tickets: DATAJPA-903.

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

@@ -23,11 +23,16 @@ import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Stream;
 
 import org.springframework.core.CollectionFactory;
+import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.converter.Converter;
+import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.data.domain.Slice;
 import org.springframework.data.projection.ProjectionFactory;
+import org.springframework.data.util.ReflectionUtils;
 import org.springframework.util.Assert;
 
 /**
@@ -127,7 +132,8 @@ public class ResultProcessor {
 
 		Assert.notNull(preparingConverter, "Preparing converter must not be null!");
 
-		ChainingConverter converter = ChainingConverter.of(type.getReturnedType(), preparingConverter).and(this.converter);
+		final ChainingConverter converter = ChainingConverter.of(type.getReturnedType(), preparingConverter)
+				.and(this.converter);
 
 		if (source instanceof Slice && method.isPageQuery() || method.isSliceQuery()) {
 			return (T) ((Slice<?>) source).map(converter);
@@ -145,6 +151,17 @@ public class ResultProcessor {
 			return (T) target;
 		}
 
+		if (ReflectionUtils.isJava8StreamType(source.getClass()) && method.isStreamQuery()) {
+
+			return (T) ((Stream<Object>) source).map(new Function<Object, T>() {
+
+				@Override
+				public T apply(Object t) {
+					return (T) (type.isInstance(t) ? t : converter.convert(t));
+				}
+			});
+		}
+
 		return (T) converter.convert(source);
 	}
 
@@ -211,6 +228,7 @@ public class ResultProcessor {
 
 		private final @NonNull ReturnedType type;
 		private final @NonNull ProjectionFactory factory;
+		private final ConversionService conversionService = new DefaultConversionService();
 
 		/* 
 		 * (non-Javadoc)
@@ -218,7 +236,14 @@ public class ResultProcessor {
 		 */
 		@Override
 		public Object convert(Object source) {
-			return factory.createProjection(type.getReturnedType(), getProjectionTarget(source));
+
+			Class<?> targetType = type.getReturnedType();
+
+			if (targetType.isInterface()) {
+				return factory.createProjection(targetType, getProjectionTarget(source));
+			}
+
+			return conversionService.convert(source, targetType);
 		}
 
 		private Object getProjectionTarget(Object source) {

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

@@ -25,6 +25,8 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import org.junit.Test;
 import org.springframework.beans.factory.annotation.Value;
@@ -183,11 +185,11 @@ public class ResultProcessorUnitTests {
 
 			@Override
 			public Object convert(Object source) {
-				return new SampleDTO();
+				return new SampleDto();
 			}
 		});
 
-		assertThat(result, is(instanceOf(SampleDTO.class)));
+		assertThat(result, is(instanceOf(SampleDto.class)));
 	}
 
 	/**
@@ -215,6 +217,34 @@ public class ResultProcessorUnitTests {
 		assertThat(content.get(0), is(instanceOf(SampleProjection.class)));
 	}
 
+	/**
+	 * @see DATACMNS-859
+	 */
+	@Test
+	public void supportsStreamAsReturnWrapper() throws Exception {
+
+		Stream<Sample> samples = Arrays.asList(new Sample("Dave", "Matthews")).stream();
+
+		Object result = getProcessor("findStreamProjection").processResult(samples);
+
+		assertThat(result, is(instanceOf(Stream.class)));
+		List<?> content = ((Stream<?>) result).collect(Collectors.toList());
+
+		assertThat(content, is(not(empty())));
+		assertThat(content.get(0), is(instanceOf(SampleProjection.class)));
+	}
+
+	/**
+	 * @see DATACMNS-860
+	 */
+	@Test
+	public void supportsWrappingDto() throws Exception {
+
+		Object result = getProcessor("findOneWrappingDto").processResult(new Sample("Dave", "Matthews"));
+
+		assertThat(result, is(instanceOf(WrappingDto.class)));
+	}
+
 	private static ResultProcessor getProcessor(String methodName, Class<?>... parameters) throws Exception {
 		return getQueryMethod(methodName, parameters).getResultProcessor();
 	}
@@ -230,13 +260,15 @@ public class ResultProcessorUnitTests {
 
 		List<Sample> findAll();
 
-		List<SampleDTO> findAllDtos();
+		List<SampleDto> findAllDtos();
 
 		List<SampleProjection> findAllProjection();
 
 		Sample findOne();
 
-		SampleDTO findOneDto();
+		SampleDto findOneDto();
+
+		WrappingDto findOneWrappingDto();
 
 		SampleProjection findOneProjection();
 
@@ -247,6 +279,8 @@ public class ResultProcessorUnitTests {
 		Slice<SampleProjection> findSliceProjection(Pageable pageable);
 
 		<T> T findOneDynamic(Class<T> type);
+
+		Stream<SampleProjection> findStreamProjection();
 	}
 
 	static class Sample {
@@ -258,10 +292,15 @@ public class ResultProcessorUnitTests {
 		}
 	}
 
-	static class SampleDTO {}
+	static class SampleDto {}
 
-	interface SampleProjection {
+	@lombok.Value
+	// Needs to be public until https://jira.spring.io/browse/SPR-14304 is resolved
+	public static class WrappingDto {
+		Sample sample;
+	}
 
+	interface SampleProjection {
 		String getLastname();
 	}