DATACMNS-610 - Extracted QueryExecutionResultHandler from RepositoryFactorySupport.

To be able to verify the conversion of List based query execution results into Sets I extracted a QueryExecutionResultHandler that applies the already implemented handling for Optional types and eventually general prost processing in case the return type declared at the repository query method doesn't match the returned value.

Added additional unit tests for Optional handling.

src/test/java/org/springframework/data/repository/core/support/QueryExecutionResultHandlerUnitTests.java

@@ -0,0 +1,123 @@
+/*
+ * Copyright 2014 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
+ *
+ *      http://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.data.repository.core.support;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+
+import java.lang.reflect.Method;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+
+import org.junit.Test;
+import org.springframework.core.MethodParameter;
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.data.repository.Repository;
+
+/**
+ * Unit tests for {@link QueryExecutionResultHandler}.
+ * 
+ * @author Oliver Gierke
+ */
+public class QueryExecutionResultHandlerUnitTests {
+
+	QueryExecutionResultHandler handler = new QueryExecutionResultHandler();
+
+	/**
+	 * @see DATACMNS-610
+	 */
+	@Test
+	public void convertsListsToSet() throws Exception {
+
+		TypeDescriptor descriptor = getTypeDescriptorFor("set");
+		List<Entity> source = Collections.singletonList(new Entity());
+
+		assertThat(handler.postProcessInvocationResult(source, descriptor), is(instanceOf(Set.class)));
+	}
+
+	/**
+	 * @see DATACMNS-483
+	 */
+	@Test
+	public void turnsNullIntoJdk8Optional() throws Exception {
+
+		Object result = handler.postProcessInvocationResult(null, getTypeDescriptorFor("jdk8Optional"));
+		assertThat(result, is((Object) Optional.empty()));
+	}
+
+	/**
+	 * @see DATACMNS-483
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void wrapsValueIntoJdk8Optional() throws Exception {
+
+		Entity entity = new Entity();
+
+		Object result = handler.postProcessInvocationResult(entity, getTypeDescriptorFor("jdk8Optional"));
+		assertThat(result, is(instanceOf(Optional.class)));
+
+		Optional<Entity> optional = (Optional<Entity>) result;
+		assertThat(optional, is(Optional.of(entity)));
+	}
+
+	/**
+	 * @see DATACMNS-483
+	 */
+	@Test
+	public void turnsNullIntoGuavaOptional() throws Exception {
+
+		Object result = handler.postProcessInvocationResult(null, getTypeDescriptorFor("guavaOptional"));
+		assertThat(result, is((Object) com.google.common.base.Optional.absent()));
+	}
+
+	/**
+	 * @see DATACMNS-483
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void wrapsValueIntoGuavaOptional() throws Exception {
+
+		Entity entity = new Entity();
+
+		Object result = handler.postProcessInvocationResult(entity, getTypeDescriptorFor("guavaOptional"));
+		assertThat(result, is(instanceOf(com.google.common.base.Optional.class)));
+
+		com.google.common.base.Optional<Entity> optional = (com.google.common.base.Optional<Entity>) result;
+		assertThat(optional, is(com.google.common.base.Optional.of(entity)));
+	}
+
+	private static TypeDescriptor getTypeDescriptorFor(String methodName) throws Exception {
+
+		Method method = Sample.class.getMethod(methodName);
+		MethodParameter parameter = new MethodParameter(method, -1);
+
+		return TypeDescriptor.nested(parameter, 0);
+	}
+
+	static interface Sample extends Repository<Entity, Long> {
+
+		Set<Entity> set();
+
+		Optional<Entity> jdk8Optional();
+
+		com.google.common.base.Optional<Entity> guavaOptional();
+	}
+
+	static class Entity {}
+}