DATACMNS-1235 - Polishing.

Introduced BeanLookup to easily create a Lazy<T>-based lookup of a unique bean by type on a ListableBeanFactory. This is in support of making it easy for downstream Spring Data modules to consume the EntityPathResolver declared in an ApplicationContext using XML configuration.

QuerydslWebConfiguration now uses a plain ObjectProvider to access the bean defined falling back to our default.

Original pull request: #265.

src/test/java/org/springframework/data/util/BeanLookupUnitTests.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2018 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.util;
+
+import static org.assertj.core.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+import org.springframework.beans.factory.ListableBeanFactory;
+import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
+import org.springframework.data.querydsl.EntityPathResolver;
+import org.springframework.data.querydsl.SimpleEntityPathResolver;
+
+/**
+ * Unit tests for {@link BeanLookup}.
+ * 
+ * @author Oliver Gierke
+ * @soundtrack Dave Matthews Band - Shotgun (DMB Live 25)
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class BeanLookupUnitTests {
+
+	@Mock ListableBeanFactory beanFactory;
+	Map<String, EntityPathResolver> beans;
+
+	@Before
+	public void setUp() {
+
+		this.beans = new HashMap<>();
+
+		doReturn(beans).when(beanFactory).getBeansOfType(EntityPathResolver.class, false, false);
+	}
+
+	@Test // DATACMNS-1235
+	public void returnsUniqueBeanByType() {
+
+		beans.put("foo", SimpleEntityPathResolver.INSTANCE);
+
+		assertThat(BeanLookup.lazyIfAvailable(EntityPathResolver.class, beanFactory).get()) //
+				.isEqualTo(SimpleEntityPathResolver.INSTANCE);
+	}
+
+	@Test // DATACMNS-1235
+	public void returnsEmptyLazyIfNoBeanAvailable() {
+		assertThat(BeanLookup.lazyIfAvailable(EntityPathResolver.class, beanFactory).getOptional()).isEmpty();
+	}
+
+	@Test // DATACMNS-1235
+	public void throwsExceptionIfMultipleBeansAreAvailable() {
+
+		beans.put("foo", SimpleEntityPathResolver.INSTANCE);
+		beans.put("bar", SimpleEntityPathResolver.INSTANCE);
+
+		assertThatExceptionOfType(NoUniqueBeanDefinitionException.class) //
+				.isThrownBy(() -> BeanLookup.lazyIfAvailable(EntityPathResolver.class, beanFactory).get()) //
+				.withMessageContaining("foo") //
+				.withMessageContaining("bar") //
+				.withMessageContaining(EntityPathResolver.class.getName());
+	}
+}