DATACMNS-764 - Java 8 polishing.

Use Streamable in configuration APIs for more efficient, lazy traversal of source lists. Introduced SelectionSet.of(…) to move away from constructors. Avoid the use of null in SelectionSet.

Original pull request: #201.

src/main/java/org/springframework/data/repository/config/AnnotationRepositoryConfigurationSource.java

@@ -18,7 +18,6 @@ package org.springframework.data.repository.config;
 import java.lang.annotation.Annotation;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
@@ -37,6 +36,7 @@ import org.springframework.core.type.filter.AspectJTypeFilter;
 import org.springframework.core.type.filter.AssignableTypeFilter;
 import org.springframework.core.type.filter.RegexPatternTypeFilter;
 import org.springframework.core.type.filter.TypeFilter;
+import org.springframework.data.util.Streamable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.StringUtils;
@@ -113,7 +113,7 @@ public class AnnotationRepositoryConfigurationSource extends RepositoryConfigura
 	 * (non-Javadoc)
 	 * @see org.springframework.data.repository.config.RepositoryConfigurationSource#getBasePackages()
 	 */
-	public Iterable<String> getBasePackages() {
+	public Streamable<String> getBasePackages() {
 
 		String[] value = attributes.getStringArray("value");
 		String[] basePackages = attributes.getStringArray(BASE_PACKAGES);
@@ -121,19 +121,20 @@ public class AnnotationRepositoryConfigurationSource extends RepositoryConfigura
 
 		// Default configuration - return package of annotated class
 		if (value.length == 0 && basePackages.length == 0 && basePackageClasses.length == 0) {
+
 			String className = configMetadata.getClassName();
-			return Collections.singleton(ClassUtils.getPackageName(className));
+			return Streamable.of(ClassUtils.getPackageName(className));
 		}
 
 		Set<String> packages = new HashSet<>();
 		packages.addAll(Arrays.asList(value));
 		packages.addAll(Arrays.asList(basePackages));
 
-		for (Class<?> typeName : basePackageClasses) {
-			packages.add(ClassUtils.getPackageName(typeName));
-		}
+		Arrays.stream(basePackageClasses)//
+				.map(ClassUtils::getPackageName)//
+				.forEach(it -> packages.add(it));
 
-		return packages;
+		return Streamable.of(packages);
 	}
 
 	/*
@@ -182,20 +183,15 @@ public class AnnotationRepositoryConfigurationSource extends RepositoryConfigura
 	 * @see org.springframework.data.repository.config.RepositoryConfigurationSourceSupport#getExcludeFilters()
 	 */
 	@Override
-	public Iterable<TypeFilter> getExcludeFilters() {
+	public Streamable<TypeFilter> getExcludeFilters() {
 		return parseFilters("excludeFilters");
 	}
 
-	private Set<TypeFilter> parseFilters(String attributeName) {
+	private Streamable<TypeFilter> parseFilters(String attributeName) {
 
-		Set<TypeFilter> result = new HashSet<>();
 		AnnotationAttributes[] filters = attributes.getAnnotationArray(attributeName);
 
-		for (AnnotationAttributes filter : filters) {
-			result.addAll(typeFiltersFor(filter));
-		}
-
-		return result;
+		return Streamable.of(() -> Arrays.stream(filters).flatMap(it -> typeFiltersFor(it).stream()));
 	}
 
 	/**

src/main/java/org/springframework/data/repository/config/CustomRepositoryImplementationDetector.java

@@ -13,16 +13,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.repository.config;
 
 import lombok.NonNull;
 import lombok.RequiredArgsConstructor;
 
-import java.util.ArrayList;
 import java.util.Collection;
-import java.util.HashSet;
-import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 import java.util.function.Function;
@@ -37,6 +33,7 @@ import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.type.classreading.MetadataReaderFactory;
 import org.springframework.core.type.filter.RegexPatternTypeFilter;
 import org.springframework.core.type.filter.TypeFilter;
+import org.springframework.data.util.Streamable;
 import org.springframework.util.Assert;
 
 /**
@@ -52,6 +49,7 @@ import org.springframework.util.Assert;
 public class CustomRepositoryImplementationDetector {
 
 	private static final String CUSTOM_IMPLEMENTATION_RESOURCE_PATTERN = "**/*%s.class";
+	private static final String AMBIGUOUS_CUSTOM_IMPLEMENTATIONS = "Ambiguous custom implementations detected! Found %s but expected a single implementation!";
 
 	private final @NonNull MetadataReaderFactory metadataReaderFactory;
 	private final @NonNull Environment environment;
@@ -94,12 +92,10 @@ public class CustomRepositoryImplementationDetector {
 
 		Set<BeanDefinition> definitions = findCandidateBeanDefinitions(className, basePackages, excludeFilters);
 
-		SelectionSet<BeanDefinition> selection = new SelectionSet<>( //
-				definitions, //
-				c -> c.isEmpty() ? null : throwAmbiguousCustomImplementationException(c) //
-		).filterIfNecessary(bd -> beanName != null && beanName.equals(beanNameGenerator.apply(bd)));
-
-		return Optional.ofNullable((AbstractBeanDefinition) selection.uniqueResult());
+		return SelectionSet //
+				.of(definitions, c -> c.isEmpty() ? Optional.empty() : throwAmbiguousCustomImplementationException(c)) //
+				.filterIfNecessary(bd -> beanName != null && beanName.equals(beanNameGenerator.apply(bd)))//
+				.uniqueResult().map(it -> AbstractBeanDefinition.class.cast(it));
 	}
 
 	Set<BeanDefinition> findCandidateBeanDefinitions(String className, Iterable<String> basePackages,
@@ -116,31 +112,20 @@ public class CustomRepositoryImplementationDetector {
 		provider.setMetadataReaderFactory(metadataReaderFactory);
 		provider.addIncludeFilter(new RegexPatternTypeFilter(pattern));
 
-		for (TypeFilter excludeFilter : excludeFilters) {
-			provider.addExcludeFilter(excludeFilter);
-		}
+		excludeFilters.forEach(it -> provider.addExcludeFilter(it));
 
-		Set<BeanDefinition> definitions = new HashSet<>();
-
-		for (String basePackage : basePackages) {
-			definitions.addAll(provider.findCandidateComponents(basePackage));
-		}
-
-		return definitions;
+		return Streamable.of(basePackages).stream()//
+				.flatMap(it -> provider.findCandidateComponents(it).stream())//
+				.collect(Collectors.toSet());
 	}
 
-	private static AbstractBeanDefinition throwAmbiguousCustomImplementationException(
+	private static Optional<BeanDefinition> throwAmbiguousCustomImplementationException(
 			Collection<BeanDefinition> definitions) {
 
-		List<String> implementationClassNames = new ArrayList<String>();
-		for (BeanDefinition bean : definitions) {
-			implementationClassNames.add(bean.getBeanClassName());
-		}
+		String implementationNames = definitions.stream()//
+				.map(BeanDefinition::getBeanClassName)//
+				.collect(Collectors.joining(", "));
 
-		throw new IllegalStateException(
-				String.format("Ambiguous custom implementations detected! Found %s but expected a single implementation!", //
-						definitions.stream()//
-								.map(BeanDefinition::getBeanClassName)//
-								.collect(Collectors.joining(", "))));
+		throw new IllegalStateException(String.format(AMBIGUOUS_CUSTOM_IMPLEMENTATIONS, implementationNames));
 	}
 }

src/main/java/org/springframework/data/repository/config/RepositoryBeanNameGenerator.java

@@ -15,10 +15,11 @@
  */
 package org.springframework.data.repository.config;
 
+import lombok.RequiredArgsConstructor;
+
 import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
 import org.springframework.beans.factory.annotation.AnnotatedGenericBeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinition;
-import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.beans.factory.support.BeanNameGenerator;
 import org.springframework.context.annotation.AnnotationBeanNameGenerator;
 import org.springframework.context.annotation.ScannedGenericBeanDefinition;
@@ -32,16 +33,13 @@ import org.springframework.util.ClassUtils;
  * @author Oliver Gierke
  * @author Jens Schauder
  */
+@RequiredArgsConstructor
 public class RepositoryBeanNameGenerator {
 
 	private static final BeanNameGenerator DELEGATE = new AnnotationBeanNameGenerator();
 
 	private final ClassLoader beanClassLoader;
 
-	public RepositoryBeanNameGenerator(ClassLoader beanClassLoader) {
-		this.beanClassLoader = beanClassLoader;
-	}
-
 	/**
 	 * Generate a bean name for the given bean definition.
 	 *
@@ -66,11 +64,13 @@ public class RepositoryBeanNameGenerator {
 	private Class<?> getRepositoryInterfaceFrom(BeanDefinition beanDefinition) {
 
 		if (beanDefinition instanceof ScannedGenericBeanDefinition) {
+
 			try {
 				return ((ScannedGenericBeanDefinition) beanDefinition).resolveBeanClass(beanClassLoader);
 			} catch (ClassNotFoundException e) {
 				throw new IllegalStateException("Could not resolve bean class.", e);
 			}
+
 		} else {
 			return getRepositoryInterfaceFromFactory(beanDefinition);
 		}
@@ -81,8 +81,11 @@ public class RepositoryBeanNameGenerator {
 		Object value = beanDefinition.getConstructorArgumentValues().getArgumentValue(0, Class.class).getValue();
 
 		if (value instanceof Class<?>) {
+
 			return (Class<?>) value;
+
 		} else {
+
 			try {
 				return ClassUtils.forName(value.toString(), beanClassLoader);
 			} catch (Exception o_O) {

src/main/java/org/springframework/data/repository/config/RepositoryConfigurationSource.java

@@ -15,13 +15,13 @@
  */
 package org.springframework.data.repository.config;
 
-import java.util.Collection;
 import java.util.Optional;
 
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.type.filter.TypeFilter;
 import org.springframework.data.repository.query.QueryLookupStrategy;
+import org.springframework.data.util.Streamable;
 
 /**
  * Interface containing the configurable options for the Spring Data repository subsystem.
@@ -46,7 +46,7 @@ public interface RepositoryConfigurationSource {
 	 * 
 	 * @return must not be {@literal null}.
 	 */
-	Iterable<String> getBasePackages();
+	Streamable<String> getBasePackages();
 
 	/**
 	 * Returns the {@link QueryLookupStrategy.Key} to define how query methods shall be resolved.
@@ -89,7 +89,7 @@ public interface RepositoryConfigurationSource {
 	 * @param loader
 	 * @return
 	 */
-	Collection<BeanDefinition> getCandidates(ResourceLoader loader);
+	Streamable<BeanDefinition> getCandidates(ResourceLoader loader);
 
 	/**
 	 * Returns the value for the {@link String} attribute with the given name. The name is expected to be handed in
@@ -115,12 +115,12 @@ public interface RepositoryConfigurationSource {
 	 *
 	 * @return must not be {@literal null}.
 	 */
-	Iterable<TypeFilter> getExcludeFilters();
+	Streamable<TypeFilter> getExcludeFilters();
 
 	/**
 	 * Returns a name for the beanDefinition.
 	 *
-	 * @param beanDefinition Must not be {@literal null}.
+	 * @param beanDefinition must not be {@literal null}.
 	 * @return
 	 * @since 2.0
 	 */

src/main/java/org/springframework/data/repository/config/RepositoryConfigurationSourceSupport.java

@@ -15,15 +15,13 @@
  */
 package org.springframework.data.repository.config;
 
-import java.util.Collection;
 import java.util.Collections;
-import java.util.HashSet;
-import java.util.Set;
 
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.core.env.Environment;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.type.filter.TypeFilter;
+import org.springframework.data.util.Streamable;
 import org.springframework.util.Assert;
 
 /**
@@ -58,27 +56,20 @@ public abstract class RepositoryConfigurationSourceSupport implements Repository
 
 	/* 
 	 * (non-Javadoc)
-	 * @see org.springframework.data.repository.config.RepositoryConfiguration#getCandidates(org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider)
+	 * @see org.springframework.data.repository.config.RepositoryConfigurationSource#getCandidates(org.springframework.core.io.ResourceLoader)
 	 */
-	public Collection<BeanDefinition> getCandidates(ResourceLoader loader) {
+	@Override
+	public Streamable<BeanDefinition> getCandidates(ResourceLoader loader) {
 
 		RepositoryComponentProvider scanner = new RepositoryComponentProvider(getIncludeFilters());
 		scanner.setConsiderNestedRepositoryInterfaces(shouldConsiderNestedRepositories());
 		scanner.setResourceLoader(loader);
 		scanner.setEnvironment(environment);
 
-		for (TypeFilter filter : getExcludeFilters()) {
-			scanner.addExcludeFilter(filter);
-		}
+		getExcludeFilters().forEach(it -> scanner.addExcludeFilter(it));
 
-		Set<BeanDefinition> result = new HashSet<>();
-
-		for (String basePackage : getBasePackages()) {
-			Set<BeanDefinition> candidate = scanner.findCandidateComponents(basePackage);
-			result.addAll(candidate);
-		}
-
-		return result;
+		return Streamable.of(() -> getBasePackages().stream()//
+				.flatMap(it -> scanner.findCandidateComponents(it).stream()));
 	}
 
 	/**
@@ -87,8 +78,18 @@ public abstract class RepositoryConfigurationSourceSupport implements Repository
 	 *
 	 * @return must not be {@literal null}.
 	 */
-	public Iterable<TypeFilter> getExcludeFilters() {
-		return Collections.emptySet();
+	@Override
+	public Streamable<TypeFilter> getExcludeFilters() {
+		return Streamable.empty();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.repository.config.RepositoryConfigurationSource#getBeanNameGenerator()
+	 */
+	@Override
+	public String generateBeanName(BeanDefinition beanDefinition) {
+		return beanNameGenerator.generateBeanName(beanDefinition);
 	}
 
 	/**
@@ -110,13 +111,4 @@ public abstract class RepositoryConfigurationSourceSupport implements Repository
 	public boolean shouldConsiderNestedRepositories() {
 		return false;
 	}
-
-	/*
-	 * (non-Javadoc)
-	 * @see org.springframework.data.repository.config.RepositoryConfigurationSource#getBeanNameGenerator()
-	 */
-	@Override
-	public String generateBeanName(BeanDefinition beanDefinition) {
-		return beanNameGenerator.generateBeanName(beanDefinition);
-	}
 }

src/main/java/org/springframework/data/repository/config/SelectionSet.java

@@ -15,8 +15,10 @@
  */
 package org.springframework.data.repository.config;
 
+import lombok.RequiredArgsConstructor;
+
 import java.util.Collection;
-import java.util.List;
+import java.util.Optional;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
@@ -26,41 +28,35 @@ import java.util.stream.Collectors;
  * filters are ignored.
  *
  * @author Jens Schauder
+ * @author Oliver Gierke
+ * @since 2.0
  */
+@RequiredArgsConstructor(staticName = "of")
 class SelectionSet<T> {
 
 	private final Collection<T> collection;
-	private final Function<Collection<T>, T> fallback;
+	private final Function<Collection<T>, Optional<T>> fallback;
 
 	/**
 	 * creates a {@link SelectionSet} with a default fallback of {@literal null}, when no element is found and an
 	 * {@link IllegalStateException} when no element is found.
 	 */
-	SelectionSet(Collection<T> collection) {
-		this(collection, defaultFallback());
+	static <T> SelectionSet<T> of(Collection<T> collection) {
+		return new SelectionSet<>(collection, defaultFallback());
 	}
 
 	/**
-	 * @param collection The collection from which a unique element will get picked.
-	 * @param fallback Will get called once {@literal #uniqueResult} gets called if no unique result can be determined.
-	 */
-	SelectionSet(Collection<T> collection, Function<Collection<T>, T> fallback) {
-
-		this.collection = collection;
-		this.fallback = fallback;
-	}
-
-	/**
-	 * If this <code>SelectionSet</code> contains exactly one element it gets returned. If no unique result can
-	 * be identified the fallback function passed in at the constructor gets called and its return value becomes
-	 * the return value of this method.
+	 * If this {@code SelectionSet} contains exactly one element it gets returned. If no unique result can be identified
+	 * the fallback function passed in at the constructor gets called and its return value becomes the return value of
+	 * this method.
 	 *
 	 * @return a unique result, or the result of the callback provided in the constructor.
 	 */
-	T uniqueResult() {
-		T uniqueResult = findUniqueResult();
+	Optional<T> uniqueResult() {
 
-		return uniqueResult != null ? uniqueResult : fallback.apply(collection);
+		Optional<T> uniqueResult = findUniqueResult();
+
+		return uniqueResult.isPresent() ? uniqueResult : fallback.apply(collection);
 	}
 
 	/**
@@ -70,26 +66,22 @@ class SelectionSet<T> {
 	 */
 	SelectionSet<T> filterIfNecessary(Predicate<T> predicate) {
 
-		if (findUniqueResult() != null) {
-			return this;
-		}
-
-		List<T> fillteredList = collection.stream().filter(predicate).collect(Collectors.toList());
-		return new SelectionSet<T>(fillteredList, fallback);
+		return findUniqueResult().map(it -> this).orElseGet(
+				() -> new SelectionSet<T>(collection.stream().filter(predicate).collect(Collectors.toList()), fallback));
 	}
 
-	private static <S> Function<Collection<S>, S> defaultFallback() {
+	private static <S> Function<Collection<S>, Optional<S>> defaultFallback() {
 
 		return c -> {
 			if (c.isEmpty()) {
-				return null;
+				return Optional.empty();
 			} else {
 				throw new IllegalStateException("More then one element in collection.");
 			}
 		};
 	}
 
-	private T findUniqueResult() {
-		return collection.size() == 1 ? collection.iterator().next() : null;
+	private Optional<T> findUniqueResult() {
+		return Optional.ofNullable(collection.size() == 1 ? collection.iterator().next() : null);
 	}
 }

src/main/java/org/springframework/data/repository/config/XmlRepositoryConfigurationSource.java

@@ -15,7 +15,6 @@
  */
 package org.springframework.data.repository.config;
 
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Optional;
 
@@ -26,6 +25,7 @@ import org.springframework.data.config.TypeFilterParser;
 import org.springframework.data.config.TypeFilterParser.Type;
 import org.springframework.data.repository.query.QueryLookupStrategy.Key;
 import org.springframework.data.util.ParsingUtils;
+import org.springframework.data.util.Streamable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 import org.w3c.dom.Element;
@@ -89,10 +89,11 @@ public class XmlRepositoryConfigurationSource extends RepositoryConfigurationSou
 	 * (non-Javadoc)
 	 * @see org.springframework.data.repository.config.RepositoryConfigurationSource#getBasePackages()
 	 */
-	public Iterable<String> getBasePackages() {
+	public Streamable<String> getBasePackages() {
 
 		String attribute = element.getAttribute(BASE_PACKAGE);
-		return Arrays.asList(StringUtils.delimitedListToStringArray(attribute, ",", " "));
+
+		return Streamable.of(StringUtils.delimitedListToStringArray(attribute, ",", " "));
 	}
 
 	/* 
@@ -125,8 +126,8 @@ public class XmlRepositoryConfigurationSource extends RepositoryConfigurationSou
 	 * @see org.springframework.data.repository.config.RepositoryConfigurationSourceSupport#getExcludeFilters()
 	 */
 	@Override
-	public Iterable<TypeFilter> getExcludeFilters() {
-		return excludeFilters;
+	public Streamable<TypeFilter> getExcludeFilters() {
+		return Streamable.of(excludeFilters);
 	}
 
 	/*