DATAREST-394, DATAREST-408 - Projections now consider collections and maps.

The ProjectingMethodInterceptor now inspects collections and maps to apply projections to collection elements and map values. Test cases inspired by a contribution of Saulo Medeiros de Araujo.

Related pull request: #152.

spring-data-rest-core/src/main/java/org/springframework/data/rest/core/projection/ProjectingMethodInterceptor.java

@@ -15,8 +15,17 @@
  */
 package org.springframework.data.rest.core.projection;
 
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
+import java.util.Map.Entry;
+
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
+import org.springframework.core.CollectionFactory;
+import org.springframework.data.util.ClassTypeInformation;
+import org.springframework.data.util.TypeInformation;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
@@ -60,9 +69,77 @@ class ProjectingMethodInterceptor implements MethodInterceptor {
 			return null;
 		}
 
-		Class<?> returnType = invocation.getMethod().getReturnType();
+		TypeInformation<?> type = ClassTypeInformation.fromReturnTypeOf(invocation.getMethod());
 
+		if (type.isCollectionLike()) {
+			return projectCollectionElements(asCollection(result), type);
+		} else if (type.isMap()) {
+			return projectMapValues((Map<?, ?>) result, type);
+		} else {
+			return getProjection(result, type.getType());
+		}
+	}
+
+	/**
+	 * Creates projections of the given {@link Collection}'s elements if necessary and returns a new collection containing
+	 * the projection results.
+	 * 
+	 * @param sources must not be {@literal null}.
+	 * @param type must not be {@literal null}.
+	 * @return
+	 */
+	private Collection<Object> projectCollectionElements(Collection<?> sources, TypeInformation<?> type) {
+
+		Collection<Object> result = CollectionFactory.createCollection(type.getType(), sources.size());
+
+		for (Object source : sources) {
+			result.add(getProjection(source, type.getComponentType().getType()));
+		}
+
+		return result;
+	}
+
+	/**
+	 * Creates projections of the given {@link Map}'s values if necessary and returns an new {@link Map} with the handled
+	 * values.
+	 * 
+	 * @param sources must not be {@literal null}.
+	 * @param type must not be {@literal null}.
+	 * @return
+	 */
+	private Map<Object, Object> projectMapValues(Map<?, ?> sources, TypeInformation<?> type) {
+
+		Map<Object, Object> result = CollectionFactory.createMap(type.getType(), sources.size());
+
+		for (Entry<?, ?> source : sources.entrySet()) {
+			result.put(source.getKey(), getProjection(source.getValue(), type.getMapValueType().getType()));
+		}
+
+		return result;
+	}
+
+	private Object getProjection(Object result, Class<?> returnType) {
 		return ClassUtils.isAssignable(returnType, result.getClass()) ? result : factory.createProjection(result,
 				returnType);
 	}
+
+	/**
+	 * Turns the given value into a {@link Collection}. Will create an empty {@link Collection} for {@literal null}, turn
+	 * an array iinto a collection an wrap all other values into a single-element collection.
+	 * 
+	 * @param source can be {@literal null}.
+	 * @return
+	 */
+	private static Collection<?> asCollection(Object source) {
+
+		if (source == null) {
+			return Collections.emptySet();
+		} else if (source instanceof Collection) {
+			return (Collection<?>) source;
+		} else if (source.getClass().isArray()) {
+			return Arrays.asList((Object[]) source);
+		} else {
+			return Collections.singleton(source);
+		}
+	}
 }

spring-data-rest-core/src/test/java/org/springframework/data/rest/core/projection/ProjectingMethodInterceptorUnitTests.java

@@ -20,8 +20,16 @@ import static org.junit.Assert.*;
 import static org.mockito.Matchers.*;
 import static org.mockito.Mockito.*;
 
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
+import org.hamcrest.Matchers;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
@@ -31,6 +39,7 @@ import org.mockito.runners.MockitoJUnitRunner;
  * Unit tests for {@link ProjectingMethodInterceptor}.
  * 
  * @author Oliver Gierke
+ * @author Saulo Medeiros de Araujo
  */
 @RunWith(MockitoJUnitRunner.class)
 public class ProjectingMethodInterceptorUnitTests {
@@ -95,6 +104,96 @@ public class ProjectingMethodInterceptorUnitTests {
 		verify(factory, times(0)).createProjection(anyObject(), (Class<?>) anyObject());
 	}
 
+	/**
+	 * @see DATAREST-394, DATAREST-408
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void appliesProjectionToNonEmptySets() throws Throwable {
+
+		MethodInterceptor methodInterceptor = new ProjectingMethodInterceptor(new ProxyProjectionFactory(null), interceptor);
+		Object result = methodInterceptor.invoke(mockInvocationOf("getHelperCollection",
+				Collections.singleton(mock(Helper.class))));
+
+		assertThat(result, is(instanceOf(Set.class)));
+
+		Set<Object> projections = (Set<Object>) result;
+		assertThat(projections, hasSize(1));
+		assertThat(projections, hasItem(instanceOf(HelperProjection.class)));
+	}
+
+	/**
+	 * @see DATAREST-394, DATAREST-408
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void appliesProjectionToNonEmptyLists() throws Throwable {
+
+		MethodInterceptor methodInterceptor = new ProjectingMethodInterceptor(new ProxyProjectionFactory(null), interceptor);
+		Object result = methodInterceptor.invoke(mockInvocationOf("getHelperList",
+				Collections.singletonList(mock(Helper.class))));
+
+		assertThat(result, is(instanceOf(List.class)));
+
+		List<Object> projections = (List<Object>) result;
+
+		assertThat(projections, hasSize(1));
+		assertThat(projections, hasItem(instanceOf(HelperProjection.class)));
+	}
+
+	/**
+	 * @see DATAREST-394, DATAREST-408
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void allowsMaskingAnArrayIntoACollection() throws Throwable {
+
+		MethodInterceptor methodInterceptor = new ProjectingMethodInterceptor(new ProxyProjectionFactory(null), interceptor);
+		Object result = methodInterceptor.invoke(mockInvocationOf("getHelperArray", new Helper[] { mock(Helper.class) }));
+
+		assertThat(result, is(instanceOf(Collection.class)));
+
+		Collection<Object> projections = (Collection<Object>) result;
+
+		assertThat(projections, hasSize(1));
+		assertThat(projections, hasItem(instanceOf(HelperProjection.class)));
+	}
+
+	/**
+	 * @see DATAREST-394, DATAREST-408
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void appliesProjectionToNonEmptyMap() throws Throwable {
+
+		MethodInterceptor methodInterceptor = new ProjectingMethodInterceptor(new ProxyProjectionFactory(null), interceptor);
+
+		Object result = methodInterceptor.invoke(mockInvocationOf("getHelperMap",
+				Collections.singletonMap("foo", mock(Helper.class))));
+
+		assertThat(result, is(instanceOf(Map.class)));
+
+		Map<String, Object> projections = (Map<String, Object>) result;
+		assertThat(projections.entrySet(), is(Matchers.<Entry<String, Object>> iterableWithSize(1)));
+		assertThat(projections, hasEntry(is("foo"), instanceOf(HelperProjection.class)));
+	}
+
+	/**
+	 * Mocks the {@link Helper} method of the given name to return the given value.
+	 * 
+	 * @param methodName
+	 * @param returnValue
+	 * @return
+	 * @throws Throwable
+	 */
+	private MethodInvocation mockInvocationOf(String methodName, Object returnValue) throws Throwable {
+
+		when(invocation.getMethod()).thenReturn(Helper.class.getMethod(methodName));
+		when(interceptor.invoke(invocation)).thenReturn(returnValue);
+
+		return invocation;
+	}
+
 	interface Helper {
 
 		Helper getHelper();
@@ -102,5 +201,21 @@ public class ProjectingMethodInterceptorUnitTests {
 		String getString();
 
 		long getPrimitive();
+
+		Collection<HelperProjection> getHelperCollection();
+
+		List<HelperProjection> getHelperList();
+
+		Set<HelperProjection> getHelperSet();
+
+		Map<String, HelperProjection> getHelperMap();
+
+		Collection<HelperProjection> getHelperArray();
+	}
+
+	interface HelperProjection {
+		Helper getHelper();
+
+		String getString();
 	}
 }