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/main/java/org/springframework/data/util/BeanLookup.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 lombok.experimental.UtilityClass;
+
+import java.util.Map;
+
+import javax.annotation.Nullable;
+
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.ListableBeanFactory;
+import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
+import org.springframework.util.Assert;
+
+/**
+ * Simple helper to allow lenient lookup of beans of a given type from a {@link ListableBeanFactory}. This is not user
+ * facing API but a mere helper for Spring Data configuration code.
+ * 
+ * @author Oliver Gierke
+ * @since 2.1
+ * @soundtrack Dave Matthews Band - Bartender (DMB Live 25)
+ */
+@UtilityClass
+public class BeanLookup {
+
+	/**
+	 * Returns a {@link Lazy} for the unique bean of the given type from the given {@link BeanFactory} (which needs to be
+	 * a {@link ListableBeanFactory}). The lookup will produce a {@link NoUniqueBeanDefinitionException} in case multiple
+	 * beans of the given type are available in the given {@link BeanFactory}.
+	 * 
+	 * @param type must not be {@literal null}.
+	 * @param beanFactory the {@link BeanFactory} to lookup the bean from.
+	 * @return a {@link Lazy} for the unique bean of the given type or the instance provided by the fallback in case no
+	 *         bean of the given type can be found.
+	 */
+	public static <T> Lazy<T> lazyIfAvailable(Class<T> type, BeanFactory beanFactory) {
+
+		Assert.notNull(type, "Type must not be null!");
+		Assert.isInstanceOf(ListableBeanFactory.class, beanFactory);
+
+		return Lazy.of(() -> lookupBean(type, (ListableBeanFactory) beanFactory));
+	}
+
+	/**
+	 * Looks up the unique bean of the given type from the given {@link ListableBeanFactory}.
+	 * 
+	 * @param type must not be {@literal null}.
+	 * @param beanFactory must not be {@literal null}.
+	 * @return
+	 */
+	@Nullable
+	private static <T> T lookupBean(Class<T> type, ListableBeanFactory beanFactory) {
+
+		Map<String, T> names = beanFactory.getBeansOfType(type, false, false);
+
+		switch (names.size()) {
+
+			case 0:
+				return null;
+			case 1:
+				return names.values().iterator().next();
+			default:
+				throw new NoUniqueBeanDefinitionException(type, names.keySet());
+		}
+	}
+}

src/main/java/org/springframework/data/web/config/QuerydslWebConfiguration.java

@@ -19,12 +19,14 @@ import java.util.List;
 import java.util.Optional;
 
 import org.springframework.beans.factory.ObjectFactory;
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.core.convert.ConversionService;
+import org.springframework.data.querydsl.EntityPathResolver;
 import org.springframework.data.querydsl.SimpleEntityPathResolver;
 import org.springframework.data.querydsl.binding.QuerydslBindingsFactory;
 import org.springframework.data.web.querydsl.QuerydslPredicateArgumentResolver;
@@ -45,6 +47,7 @@ import com.querydsl.core.types.Predicate;
 public class QuerydslWebConfiguration implements WebMvcConfigurer {
 
 	@Autowired @Qualifier("mvcConversionService") ObjectFactory<ConversionService> conversionService;
+	@Autowired ObjectProvider<EntityPathResolver> resolver;
 
 	/**
 	 * Default {@link QuerydslPredicateArgumentResolver} to create Querydsl {@link Predicate} instances for Spring MVC
@@ -61,7 +64,7 @@ public class QuerydslWebConfiguration implements WebMvcConfigurer {
 	@Lazy
 	@Bean
 	public QuerydslBindingsFactory querydslBindingsFactory() {
-		return new QuerydslBindingsFactory(SimpleEntityPathResolver.INSTANCE);
+		return new QuerydslBindingsFactory(resolver.getIfUnique(() -> SimpleEntityPathResolver.INSTANCE));
 	}
 
 	/*

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());
+	}
+}

src/test/java/org/springframework/data/web/config/EnableSpringDataWebSupportIntegrationTests.java

@@ -30,6 +30,9 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.data.classloadersupport.HidingClassLoader;
 import org.springframework.data.geo.Distance;
 import org.springframework.data.geo.Point;
+import org.springframework.data.querydsl.EntityPathResolver;
+import org.springframework.data.querydsl.SimpleEntityPathResolver;
+import org.springframework.data.querydsl.binding.QuerydslBindingsFactory;
 import org.springframework.data.web.PageableHandlerMethodArgumentResolver;
 import org.springframework.data.web.PagedResourcesAssemblerArgumentResolver;
 import org.springframework.data.web.ProxyingHandlerMethodArgumentResolver;
@@ -88,6 +91,18 @@ public class EnableSpringDataWebSupportIntegrationTests {
 		}
 	}
 
+	@Configuration
+	@EnableSpringDataWebSupport
+	static class CustomEntityPathResolver {
+
+		static SimpleEntityPathResolver resolver = new SimpleEntityPathResolver("suffix");
+
+		@Bean
+		SimpleEntityPathResolver entityPathResolver() {
+			return resolver;
+		}
+	}
+
 	@Test // DATACMNS-330
 	public void registersBasicBeanDefinitions() throws Exception {
 
@@ -215,6 +230,16 @@ public class EnableSpringDataWebSupportIntegrationTests {
 		assertThat(adapter.getArgumentResolvers().get(0)).isInstanceOf(ProxyingHandlerMethodArgumentResolver.class);
 	}
 
+	@Test // DATACMNS-1235
+	public void picksUpEntityPathResolverIfRegistered() {
+
+		WebApplicationContext context = WebTestUtils.createApplicationContext(CustomEntityPathResolver.class);
+
+		assertThat(context.getBean(EntityPathResolver.class)).isEqualTo(CustomEntityPathResolver.resolver);
+		assertThat(context.getBean(QuerydslBindingsFactory.class).getEntityPathResolver())
+				.isEqualTo(CustomEntityPathResolver.resolver);
+	}
+
 	private static void assertResolversRegistered(ApplicationContext context, Class<?>... resolverTypes) {
 
 		RequestMappingHandlerAdapter adapter = context.getBean(RequestMappingHandlerAdapter.class);