DATAREST-511 - Support for executing repository methods returning Optionals.

Added an UnwrappingRepositoryInvokerFactory that transparently unwraps JDK 8 and Guava Optionals to make sure the consuming code works with values or plain nulls correctly.

spring-data-rest-core/src/test/java/org/springframework/data/rest/core/support/UnwrappingRepositoryInvokerFactoryUnitTests.java

@@ -0,0 +1,105 @@
+/*
+ * Copyright 2015 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.rest.core.support;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
+
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Optional;
+
+import org.hamcrest.Matcher;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
+import org.springframework.data.repository.support.RepositoryInvoker;
+import org.springframework.data.repository.support.RepositoryInvokerFactory;
+import org.springframework.util.LinkedMultiValueMap;
+
+/**
+ * Unit tests for {@link UnwrappingRepositoryInvokerFactory}.
+ * 
+ * @author Oliver Gierke
+ */
+@RunWith(Parameterized.class)
+public class UnwrappingRepositoryInvokerFactoryUnitTests {
+
+	static final Object REFERENCE = new Object();
+
+	RepositoryInvokerFactory delegate = mock(RepositoryInvokerFactory.class);
+	RepositoryInvoker invoker = mock(RepositoryInvoker.class);
+
+	RepositoryInvokerFactory factory;
+	Method method;
+
+	public @Parameter(value = 0) Object source;
+	public @Parameter(value = 1) Matcher<Object> value;
+
+	@Before
+	public void setUp() throws Exception {
+
+		when(delegate.getInvokerFor(Object.class)).thenReturn(invoker);
+
+		this.factory = new UnwrappingRepositoryInvokerFactory(delegate);
+		this.method = Object.class.getMethod("toString");
+	}
+
+	@Parameters
+	public static Collection<Object[]> data() {
+		return Arrays.asList(new Object[][] { //
+				{ Optional.empty(), is(nullValue()) }, //
+						{ Optional.of(REFERENCE), is(REFERENCE) }, //
+						{ com.google.common.base.Optional.absent(), is(nullValue()) }, //
+						{ com.google.common.base.Optional.of(REFERENCE), is(REFERENCE) } //
+				});
+	}
+
+	/**
+	 * @see DATAREST-511
+	 */
+	@Test
+	public void unwrapsValuesForFindOne() {
+		assertFindOneValueForSource(source, value);
+	}
+
+	/**
+	 * @see DATAREST-511
+	 */
+	@Test
+	public void unwrapsValuesForQuery() {
+		assertQueryValueForSource(source, value);
+	}
+
+	private void assertFindOneValueForSource(Object source, Matcher<Object> value) {
+
+		when(invoker.invokeFindOne(1L)).thenReturn(source);
+		assertThat(factory.getInvokerFor(Object.class).invokeFindOne(1L), value);
+	}
+
+	private void assertQueryValueForSource(Object source, Matcher<Object> value) {
+
+		when(invoker.invokeQueryMethod(method, new LinkedMultiValueMap<String, Object>(), null, null)).thenReturn(source);
+		assertThat(
+				factory.getInvokerFor(Object.class).invokeQueryMethod(method, new LinkedMultiValueMap<String, Object>(), null,
+						null), value);
+	}
+}