https://github.com/spring-projects/spring-framework: Spring Context (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2018 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.context.annotation;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.net.UnknownHostException;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.parsing.Location;
import org.springframework.beans.factory.parsing.Problem;
import org.springframework.beans.factory.parsing.ProblemReporter;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionReader;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.context.annotation.ConfigurationCondition.ConfigurationPhase;
import org.springframework.context.annotation.DeferredImportSelector.Group;
import org.springframework.core.NestedIOException;
import org.springframework.core.OrderComparator;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.core.env.CompositePropertySource;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.Environment;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.DefaultPropertySourceFactory;
import org.springframework.core.io.support.EncodedResource;
import org.springframework.core.io.support.PropertySourceFactory;
import org.springframework.core.io.support.ResourcePropertySource;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.core.type.MethodMetadata;
import org.springframework.core.type.StandardAnnotationMetadata;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.core.type.filter.AssignableTypeFilter;
import org.springframework.lang.Nullable;
import org.springframework.stereotype.Component;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StringUtils;


Parses a Configuration class definition, populating a collection of ConfigurationClass objects (parsing a single Configuration class may result in any number of ConfigurationClass objects because one Configuration class may import another using the Import annotation). 
This class helps separate the concern of parsing the structure of a Configuration class from the concern of registering BeanDefinition objects based on the content of that model (with the exception of @ComponentScan annotations which need to be registered immediately). 
This ASM-based implementation avoids reflection and eager class loading in order to
interoperate effectively with lazy class loading in a Spring ApplicationContext.

Author:Chris Beams, Juergen Hoeller, Phillip Webb, Sam Brannen, Stephane Nicoll
See Also:
Since:3.0
/**
 * Parses a {@link Configuration} class definition, populating a collection of
 * {@link ConfigurationClass} objects (parsing a single Configuration class may result in
 * any number of ConfigurationClass objects because one Configuration class may import
 * another using the {@link Import} annotation).
 *
 * <p>This class helps separate the concern of parsing the structure of a Configuration
 * class from the concern of registering BeanDefinition objects based on the content of
 * that model (with the exception of {@code @ComponentScan} annotations which need to be
 * registered immediately).
 *
 * <p>This ASM-based implementation avoids reflection and eager class loading in order to
 * interoperate effectively with lazy class loading in a Spring ApplicationContext.
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @author Phillip Webb
 * @author Sam Brannen
 * @author Stephane Nicoll
 * @since 3.0
 * @see ConfigurationClassBeanDefinitionReader
 */
class ConfigurationClassParser {

	private static final PropertySourceFactory DEFAULT_PROPERTY_SOURCE_FACTORY = new DefaultPropertySourceFactory();

	private static final Comparator<DeferredImportSelectorHolder> DEFERRED_IMPORT_COMPARATOR =
			(o1, o2) -> AnnotationAwareOrderComparator.INSTANCE.compare(o1.getImportSelector(), o2.getImportSelector());


	private final Log logger = LogFactory.getLog(getClass());

	private final MetadataReaderFactory metadataReaderFactory;

	private final ProblemReporter problemReporter;

	private final Environment environment;

	private final ResourceLoader resourceLoader;

	private final BeanDefinitionRegistry registry;

	private final ComponentScanAnnotationParser componentScanParser;

	private final ConditionEvaluator conditionEvaluator;

	private final Map<ConfigurationClass, ConfigurationClass> configurationClasses = new LinkedHashMap<>();

	private final Map<String, ConfigurationClass> knownSuperclasses = new HashMap<>();

	private final List<String> propertySourceNames = new ArrayList<>();

	private final ImportStack importStack = new ImportStack();

	private final DeferredImportSelectorHandler deferredImportSelectorHandler = new DeferredImportSelectorHandler();


	
Create a new ConfigurationClassParser instance that will be used to populate the set of configuration classes. 
/**
	 * Create a new {@link ConfigurationClassParser} instance that will be used
	 * to populate the set of configuration classes.
	 */
	public ConfigurationClassParser(MetadataReaderFactory metadataReaderFactory,
			ProblemReporter problemReporter, Environment environment, ResourceLoader resourceLoader,
			BeanNameGenerator componentScanBeanNameGenerator, BeanDefinitionRegistry registry) {

		this.metadataReaderFactory = metadataReaderFactory;
		this.problemReporter = problemReporter;
		this.environment = environment;
		this.resourceLoader = resourceLoader;
		this.registry = registry;
		this.componentScanParser = new ComponentScanAnnotationParser(
				environment, resourceLoader, componentScanBeanNameGenerator, registry);
		this.conditionEvaluator = new ConditionEvaluator(registry, environment, resourceLoader);
	}


	public void parse(Set<BeanDefinitionHolder> configCandidates) {
		for (BeanDefinitionHolder holder : configCandidates) {
			BeanDefinition bd = holder.getBeanDefinition();
			try {
				if (bd instanceof AnnotatedBeanDefinition) {
					parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
				}
				else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
					parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
				}
				else {
					parse(bd.getBeanClassName(), holder.getBeanName());
				}
			}
			catch (BeanDefinitionStoreException ex) {
				throw ex;
			}
			catch (Throwable ex) {
				throw new BeanDefinitionStoreException(
						"Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
			}
		}

		this.deferredImportSelectorHandler.process();
	}

	protected final void parse(@Nullable String className, String beanName) throws IOException {
		Assert.notNull(className, "No bean class name for configuration class bean definition");
		MetadataReader reader = this.metadataReaderFactory.getMetadataReader(className);
		processConfigurationClass(new ConfigurationClass(reader, beanName));
	}

	protected final void parse(Class<?> clazz, String beanName) throws IOException {
		processConfigurationClass(new ConfigurationClass(clazz, beanName));
	}

	protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {
		processConfigurationClass(new ConfigurationClass(metadata, beanName));
	}

	
Validate each ConfigurationClass object. 
See Also:
/**
	 * Validate each {@link ConfigurationClass} object.
	 * @see ConfigurationClass#validate
	 */
	public void validate() {
		for (ConfigurationClass configClass : this.configurationClasses.keySet()) {
			configClass.validate(this.problemReporter);
		}
	}

	public Set<ConfigurationClass> getConfigurationClasses() {
		return this.configurationClasses.keySet();
	}


	protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
		if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
			return;
		}

		ConfigurationClass existingClass = this.configurationClasses.get(configClass);
		if (existingClass != null) {
			if (configClass.isImported()) {
				if (existingClass.isImported()) {
					existingClass.mergeImportedBy(configClass);
				}
				// Otherwise ignore new imported config class; existing non-imported class overrides it.
				return;
			}
			else {
				// Explicit bean definition found, probably replacing an import.
				// Let's remove the old one and go with the new one.
				this.configurationClasses.remove(configClass);
				this.knownSuperclasses.values().removeIf(configClass::equals);
			}
		}

		// Recursively process the configuration class and its superclass hierarchy.
		SourceClass sourceClass = asSourceClass(configClass);
		do {
			sourceClass = doProcessConfigurationClass(configClass, sourceClass);
		}
		while (sourceClass != null);

		this.configurationClasses.put(configClass, configClass);
	}

	
Apply processing and build a complete ConfigurationClass by reading the annotations, members and methods from the source class. This method can be called multiple times as relevant sources are discovered. 
Params:
  • configClass – the configuration class being build
  • sourceClass – a source class
Returns:the superclass, or null if none found or previously processed
/**
	 * Apply processing and build a complete {@link ConfigurationClass} by reading the
	 * annotations, members and methods from the source class. This method can be called
	 * multiple times as relevant sources are discovered.
	 * @param configClass the configuration class being build
	 * @param sourceClass a source class
	 * @return the superclass, or {@code null} if none found or previously processed
	 */
	@Nullable
	protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
			throws IOException {

		if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
			// Recursively process any member (nested) classes first
			processMemberClasses(configClass, sourceClass);
		}

		// Process any @PropertySource annotations
		for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
				sourceClass.getMetadata(), PropertySources.class,
				org.springframework.context.annotation.PropertySource.class)) {
			if (this.environment instanceof ConfigurableEnvironment) {
				processPropertySource(propertySource);
			}
			else {
				logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
						"]. Reason: Environment must implement ConfigurableEnvironment");
			}
		}

		// Process any @ComponentScan annotations
		Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
				sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
		if (!componentScans.isEmpty() &&
				!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
			for (AnnotationAttributes componentScan : componentScans) {
				// The config class is annotated with @ComponentScan -> perform the scan immediately
				Set<BeanDefinitionHolder> scannedBeanDefinitions =
						this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
				// Check the set of scanned definitions for any further config classes and parse recursively if needed
				for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
					BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
					if (bdCand == null) {
						bdCand = holder.getBeanDefinition();
					}
					if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
						parse(bdCand.getBeanClassName(), holder.getBeanName());
					}
				}
			}
		}

		// Process any @Import annotations
		processImports(configClass, sourceClass, getImports(sourceClass), true);

		// Process any @ImportResource annotations
		AnnotationAttributes importResource =
				AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
		if (importResource != null) {
			String[] resources = importResource.getStringArray("locations");
			Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
			for (String resource : resources) {
				String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
				configClass.addImportedResource(resolvedResource, readerClass);
			}
		}

		// Process individual @Bean methods
		Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
		for (MethodMetadata methodMetadata : beanMethods) {
			configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
		}

		// Process default methods on interfaces
		processInterfaces(configClass, sourceClass);

		// Process superclass, if any
		if (sourceClass.getMetadata().hasSuperClass()) {
			String superclass = sourceClass.getMetadata().getSuperClassName();
			if (superclass != null && !superclass.startsWith("java") &&
					!this.knownSuperclasses.containsKey(superclass)) {
				this.knownSuperclasses.put(superclass, configClass);
				// Superclass found, return its annotation metadata and recurse
				return sourceClass.getSuperClass();
			}
		}

		// No superclass -> processing is complete
		return null;
	}

	
Register member (nested) classes that happen to be configuration classes themselves.

/**
	 * Register member (nested) classes that happen to be configuration classes themselves.
	 */
	private void processMemberClasses(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {
		Collection<SourceClass> memberClasses = sourceClass.getMemberClasses();
		if (!memberClasses.isEmpty()) {
			List<SourceClass> candidates = new ArrayList<>(memberClasses.size());
			for (SourceClass memberClass : memberClasses) {
				if (ConfigurationClassUtils.isConfigurationCandidate(memberClass.getMetadata()) &&
						!memberClass.getMetadata().getClassName().equals(configClass.getMetadata().getClassName())) {
					candidates.add(memberClass);
				}
			}
			OrderComparator.sort(candidates);
			for (SourceClass candidate : candidates) {
				if (this.importStack.contains(configClass)) {
					this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
				}
				else {
					this.importStack.push(configClass);
					try {
						processConfigurationClass(candidate.asConfigClass(configClass));
					}
					finally {
						this.importStack.pop();
					}
				}
			}
		}
	}

	
Register default methods on interfaces implemented by the configuration class.

/**
	 * Register default methods on interfaces implemented by the configuration class.
	 */
	private void processInterfaces(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {
		for (SourceClass ifc : sourceClass.getInterfaces()) {
			Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(ifc);
			for (MethodMetadata methodMetadata : beanMethods) {
				if (!methodMetadata.isAbstract()) {
					// A default method or other concrete method on a Java 8+ interface...
					configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
				}
			}
			processInterfaces(configClass, ifc);
		}
	}

	
Retrieve the metadata for all @Bean methods.

/**
	 * Retrieve the metadata for all <code>@Bean</code> methods.
	 */
	private Set<MethodMetadata> retrieveBeanMethodMetadata(SourceClass sourceClass) {
		AnnotationMetadata original = sourceClass.getMetadata();
		Set<MethodMetadata> beanMethods = original.getAnnotatedMethods(Bean.class.getName());
		if (beanMethods.size() > 1 && original instanceof StandardAnnotationMetadata) {
			// Try reading the class file via ASM for deterministic declaration order...
			// Unfortunately, the JVM's standard reflection returns methods in arbitrary
			// order, even between different runs of the same application on the same JVM.
			try {
				AnnotationMetadata asm =
						this.metadataReaderFactory.getMetadataReader(original.getClassName()).getAnnotationMetadata();
				Set<MethodMetadata> asmMethods = asm.getAnnotatedMethods(Bean.class.getName());
				if (asmMethods.size() >= beanMethods.size()) {
					Set<MethodMetadata> selectedMethods = new LinkedHashSet<>(asmMethods.size());
					for (MethodMetadata asmMethod : asmMethods) {
						for (MethodMetadata beanMethod : beanMethods) {
							if (beanMethod.getMethodName().equals(asmMethod.getMethodName())) {
								selectedMethods.add(beanMethod);
								break;
							}
						}
					}
					if (selectedMethods.size() == beanMethods.size()) {
						// All reflection-detected methods found in ASM method set -> proceed
						beanMethods = selectedMethods;
					}
				}
			}
			catch (IOException ex) {
				logger.debug("Failed to read class file via ASM for determining @Bean method order", ex);
				// No worries, let's continue with the reflection metadata we started with...
			}
		}
		return beanMethods;
	}


	
Process the given @PropertySource annotation metadata.

Params:
  • propertySource – metadata for the @PropertySource annotation found
Throws:
/**
	 * Process the given <code>@PropertySource</code> annotation metadata.
	 * @param propertySource metadata for the <code>@PropertySource</code> annotation found
	 * @throws IOException if loading a property source failed
	 */
	private void processPropertySource(AnnotationAttributes propertySource) throws IOException {
		String name = propertySource.getString("name");
		if (!StringUtils.hasLength(name)) {
			name = null;
		}
		String encoding = propertySource.getString("encoding");
		if (!StringUtils.hasLength(encoding)) {
			encoding = null;
		}
		String[] locations = propertySource.getStringArray("value");
		Assert.isTrue(locations.length > 0, "At least one @PropertySource(value) location is required");
		boolean ignoreResourceNotFound = propertySource.getBoolean("ignoreResourceNotFound");

		Class<? extends PropertySourceFactory> factoryClass = propertySource.getClass("factory");
		PropertySourceFactory factory = (factoryClass == PropertySourceFactory.class ?
				DEFAULT_PROPERTY_SOURCE_FACTORY : BeanUtils.instantiateClass(factoryClass));

		for (String location : locations) {
			try {
				String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);
				Resource resource = this.resourceLoader.getResource(resolvedLocation);
				addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));
			}
			catch (IllegalArgumentException | FileNotFoundException | UnknownHostException ex) {
				// Placeholders not resolvable or resource not found when trying to open it
				if (ignoreResourceNotFound) {
					if (logger.isInfoEnabled()) {
						logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
					}
				}
				else {
					throw ex;
				}
			}
		}
	}

	private void addPropertySource(PropertySource<?> propertySource) {
		String name = propertySource.getName();
		MutablePropertySources propertySources = ((ConfigurableEnvironment) this.environment).getPropertySources();

		if (this.propertySourceNames.contains(name)) {
			// We've already added a version, we need to extend it
			PropertySource<?> existing = propertySources.get(name);
			if (existing != null) {
				PropertySource<?> newSource = (propertySource instanceof ResourcePropertySource ?
						((ResourcePropertySource) propertySource).withResourceName() : propertySource);
				if (existing instanceof CompositePropertySource) {
					((CompositePropertySource) existing).addFirstPropertySource(newSource);
				}
				else {
					if (existing instanceof ResourcePropertySource) {
						existing = ((ResourcePropertySource) existing).withResourceName();
					}
					CompositePropertySource composite = new CompositePropertySource(name);
					composite.addPropertySource(newSource);
					composite.addPropertySource(existing);
					propertySources.replace(name, composite);
				}
				return;
			}
		}

		if (this.propertySourceNames.isEmpty()) {
			propertySources.addLast(propertySource);
		}
		else {
			String firstProcessed = this.propertySourceNames.get(this.propertySourceNames.size() - 1);
			propertySources.addBefore(firstProcessed, propertySource);
		}
		this.propertySourceNames.add(name);
	}


	
Returns @Import class, considering all meta-annotations. 
/**
	 * Returns {@code @Import} class, considering all meta-annotations.
	 */
	private Set<SourceClass> getImports(SourceClass sourceClass) throws IOException {
		Set<SourceClass> imports = new LinkedHashSet<>();
		Set<SourceClass> visited = new LinkedHashSet<>();
		collectImports(sourceClass, imports, visited);
		return imports;
	}

	
Recursively collect all declared @Import values. Unlike most meta-annotations it is valid to have several @Imports declared with different values; the usual process of returning values from the first meta-annotation on a class is not sufficient. 
For example, it is common for a @Configuration class to declare direct @Imports in addition to meta-imports originating from an @Enable annotation. 
Params:
  • sourceClass – the class to search
  • imports – the imports collected so far
  • visited – used to track visited classes to prevent infinite recursion
Throws:
  • IOException – if there is any problem reading metadata from the named class
/**
	 * Recursively collect all declared {@code @Import} values. Unlike most
	 * meta-annotations it is valid to have several {@code @Import}s declared with
	 * different values; the usual process of returning values from the first
	 * meta-annotation on a class is not sufficient.
	 * <p>For example, it is common for a {@code @Configuration} class to declare direct
	 * {@code @Import}s in addition to meta-imports originating from an {@code @Enable}
	 * annotation.
	 * @param sourceClass the class to search
	 * @param imports the imports collected so far
	 * @param visited used to track visited classes to prevent infinite recursion
	 * @throws IOException if there is any problem reading metadata from the named class
	 */
	private void collectImports(SourceClass sourceClass, Set<SourceClass> imports, Set<SourceClass> visited)
			throws IOException {

		if (visited.add(sourceClass)) {
			for (SourceClass annotation : sourceClass.getAnnotations()) {
				String annName = annotation.getMetadata().getClassName();
				if (!annName.startsWith("java") && !annName.equals(Import.class.getName())) {
					collectImports(annotation, imports, visited);
				}
			}
			imports.addAll(sourceClass.getAnnotationAttributes(Import.class.getName(), "value"));
		}
	}



	private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
			Collection<SourceClass> importCandidates, boolean checkForCircularImports) {

		if (importCandidates.isEmpty()) {
			return;
		}

		if (checkForCircularImports && isChainedImportOnStack(configClass)) {
			this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
		}
		else {
			this.importStack.push(configClass);
			try {
				for (SourceClass candidate : importCandidates) {
					if (candidate.isAssignable(ImportSelector.class)) {
						// Candidate class is an ImportSelector -> delegate to it to determine imports
						Class<?> candidateClass = candidate.loadClass();
						ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);
						ParserStrategyUtils.invokeAwareMethods(
								selector, this.environment, this.resourceLoader, this.registry);
						if (selector instanceof DeferredImportSelector) {
							this.deferredImportSelectorHandler.handle(
									configClass, (DeferredImportSelector) selector);
						}
						else {
							String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
							Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames);
							processImports(configClass, currentSourceClass, importSourceClasses, false);
						}
					}
					else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
						// Candidate class is an ImportBeanDefinitionRegistrar ->
						// delegate to it to register additional bean definitions
						Class<?> candidateClass = candidate.loadClass();
						ImportBeanDefinitionRegistrar registrar =
								BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);
						ParserStrategyUtils.invokeAwareMethods(
								registrar, this.environment, this.resourceLoader, this.registry);
						configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
					}
					else {
						// Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->
						// process it as an @Configuration class
						this.importStack.registerImport(
								currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
						processConfigurationClass(candidate.asConfigClass(configClass));
					}
				}
			}
			catch (BeanDefinitionStoreException ex) {
				throw ex;
			}
			catch (Throwable ex) {
				throw new BeanDefinitionStoreException(
						"Failed to process import candidates for configuration class [" +
						configClass.getMetadata().getClassName() + "]", ex);
			}
			finally {
				this.importStack.pop();
			}
		}
	}

	private boolean isChainedImportOnStack(ConfigurationClass configClass) {
		if (this.importStack.contains(configClass)) {
			String configClassName = configClass.getMetadata().getClassName();
			AnnotationMetadata importingClass = this.importStack.getImportingClassFor(configClassName);
			while (importingClass != null) {
				if (configClassName.equals(importingClass.getClassName())) {
					return true;
				}
				importingClass = this.importStack.getImportingClassFor(importingClass.getClassName());
			}
		}
		return false;
	}

	ImportRegistry getImportRegistry() {
		return this.importStack;
	}


	
Factory method to obtain a SourceClass from a ConfigurationClass. 
/**
	 * Factory method to obtain a {@link SourceClass} from a {@link ConfigurationClass}.
	 */
	private SourceClass asSourceClass(ConfigurationClass configurationClass) throws IOException {
		AnnotationMetadata metadata = configurationClass.getMetadata();
		if (metadata instanceof StandardAnnotationMetadata) {
			return asSourceClass(((StandardAnnotationMetadata) metadata).getIntrospectedClass());
		}
		return asSourceClass(metadata.getClassName());
	}

	
Factory method to obtain a SourceClass from a Class. 
/**
	 * Factory method to obtain a {@link SourceClass} from a {@link Class}.
	 */
	SourceClass asSourceClass(@Nullable Class<?> classType) throws IOException {
		if (classType == null) {
			return new SourceClass(Object.class);
		}
		try {
			// Sanity test that we can reflectively read annotations,
			// including Class attributes; if not -> fall back to ASM
			for (Annotation ann : classType.getAnnotations()) {
				AnnotationUtils.validateAnnotation(ann);
			}
			return new SourceClass(classType);
		}
		catch (Throwable ex) {
			// Enforce ASM via class name resolution
			return asSourceClass(classType.getName());
		}
	}

	
Factory method to obtain SourceClasss from class names. 
/**
	 * Factory method to obtain {@link SourceClass SourceClasss} from class names.
	 */
	private Collection<SourceClass> asSourceClasses(String... classNames) throws IOException {
		List<SourceClass> annotatedClasses = new ArrayList<>(classNames.length);
		for (String className : classNames) {
			annotatedClasses.add(asSourceClass(className));
		}
		return annotatedClasses;
	}

	
Factory method to obtain a SourceClass from a class name. 
/**
	 * Factory method to obtain a {@link SourceClass} from a class name.
	 */
	SourceClass asSourceClass(@Nullable String className) throws IOException {
		if (className == null) {
			return new SourceClass(Object.class);
		}
		if (className.startsWith("java")) {
			// Never use ASM for core java types
			try {
				return new SourceClass(ClassUtils.forName(className, this.resourceLoader.getClassLoader()));
			}
			catch (ClassNotFoundException ex) {
				throw new NestedIOException("Failed to load class [" + className + "]", ex);
			}
		}
		return new SourceClass(this.metadataReaderFactory.getMetadataReader(className));
	}


	@SuppressWarnings("serial")
	private static class ImportStack extends ArrayDeque<ConfigurationClass> implements ImportRegistry {

		private final MultiValueMap<String, AnnotationMetadata> imports = new LinkedMultiValueMap<>();

		public void registerImport(AnnotationMetadata importingClass, String importedClass) {
			this.imports.add(importedClass, importingClass);
		}

		@Override
		@Nullable
		public AnnotationMetadata getImportingClassFor(String importedClass) {
			return CollectionUtils.lastElement(this.imports.get(importedClass));
		}

		@Override
		public void removeImportingClass(String importingClass) {
			for (List<AnnotationMetadata> list : this.imports.values()) {
				for (Iterator<AnnotationMetadata> iterator = list.iterator(); iterator.hasNext();) {
					if (iterator.next().getClassName().equals(importingClass)) {
						iterator.remove();
						break;
					}
				}
			}
		}

		
Given a stack containing (in order)

    

  • com.acme.Foo
    • 

  • com.acme.Bar
    • 

  • com.acme.Baz
    • 


return "[Foo->Bar->Baz]".

/**
		 * Given a stack containing (in order)
		 * <ul>
		 * <li>com.acme.Foo</li>
		 * <li>com.acme.Bar</li>
		 * <li>com.acme.Baz</li>
		 * </ul>
		 * return "[Foo->Bar->Baz]".
		 */
		@Override
		public String toString() {
			StringBuilder builder = new StringBuilder("[");
			Iterator<ConfigurationClass> iterator = iterator();
			while (iterator.hasNext()) {
				builder.append(iterator.next().getSimpleName());
				if (iterator.hasNext()) {
					builder.append("->");
				}
			}
			return builder.append(']').toString();
		}
	}


	private class DeferredImportSelectorHandler {

		@Nullable
		private List<DeferredImportSelectorHolder> deferredImportSelectors = new ArrayList<>();

		
Handle the specified DeferredImportSelector. If deferred import selectors are being collected, this registers this instance to the list. If they are being processed, the DeferredImportSelector is also processed immediately according to its Group. 
Params:
  • configClass – the source configuration class
  • importSelector – the selector to handle
/**
		 * Handle the specified {@link DeferredImportSelector}. If deferred import
		 * selectors are being collected, this registers this instance to the list. If
		 * they are being processed, the {@link DeferredImportSelector} is also processed
		 * immediately according to its {@link DeferredImportSelector.Group}.
		 * @param configClass the source configuration class
		 * @param importSelector the selector to handle
		 */
		public void handle(ConfigurationClass configClass, DeferredImportSelector importSelector) {
			DeferredImportSelectorHolder holder = new DeferredImportSelectorHolder(
					configClass, importSelector);
			if (this.deferredImportSelectors == null) {
				DeferredImportSelectorGroupingHandler handler = new DeferredImportSelectorGroupingHandler();
				handler.register(holder);
				handler.processGroupImports();
			}
			else {
				this.deferredImportSelectors.add(holder);
			}
		}

		public void process() {
			List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;
			this.deferredImportSelectors = null;
			try {
				if (deferredImports != null) {
					DeferredImportSelectorGroupingHandler handler = new DeferredImportSelectorGroupingHandler();
					deferredImports.sort(DEFERRED_IMPORT_COMPARATOR);
					deferredImports.forEach(handler::register);
					handler.processGroupImports();
				}
			}
			finally {
				this.deferredImportSelectors = new ArrayList<>();
			}
		}

	}


	private class DeferredImportSelectorGroupingHandler {

		private final Map<Object, DeferredImportSelectorGrouping> groupings = new LinkedHashMap<>();

		private final Map<AnnotationMetadata, ConfigurationClass> configurationClasses = new HashMap<>();

		public void register(DeferredImportSelectorHolder deferredImport) {
			Class<? extends Group> group = deferredImport.getImportSelector()
					.getImportGroup();
			DeferredImportSelectorGrouping grouping = this.groupings.computeIfAbsent(
					(group != null ? group : deferredImport),
					key -> new DeferredImportSelectorGrouping(createGroup(group)));
			grouping.add(deferredImport);
			this.configurationClasses.put(deferredImport.getConfigurationClass().getMetadata(),
					deferredImport.getConfigurationClass());
		}

		public void processGroupImports() {
			for (DeferredImportSelectorGrouping grouping : this.groupings.values()) {
				grouping.getImports().forEach(entry -> {
					ConfigurationClass configurationClass = this.configurationClasses.get(
							entry.getMetadata());
					try {
						processImports(configurationClass, asSourceClass(configurationClass),
								asSourceClasses(entry.getImportClassName()), false);
					}
					catch (BeanDefinitionStoreException ex) {
						throw ex;
					}
					catch (Throwable ex) {
						throw new BeanDefinitionStoreException(
								"Failed to process import candidates for configuration class [" +
										configurationClass.getMetadata().getClassName() + "]", ex);
					}
				});
			}
		}

		private Group createGroup(@Nullable Class<? extends Group> type) {
			Class<? extends Group> effectiveType = (type != null ? type
					: DefaultDeferredImportSelectorGroup.class);
			Group group = BeanUtils.instantiateClass(effectiveType);
			ParserStrategyUtils.invokeAwareMethods(group,
					ConfigurationClassParser.this.environment,
					ConfigurationClassParser.this.resourceLoader,
					ConfigurationClassParser.this.registry);
			return group;
		}

	}


	private static class DeferredImportSelectorHolder {

		private final ConfigurationClass configurationClass;

		private final DeferredImportSelector importSelector;

		public DeferredImportSelectorHolder(ConfigurationClass configClass, DeferredImportSelector selector) {
			this.configurationClass = configClass;
			this.importSelector = selector;
		}

		public ConfigurationClass getConfigurationClass() {
			return this.configurationClass;
		}

		public DeferredImportSelector getImportSelector() {
			return this.importSelector;
		}
	}


	private static class DeferredImportSelectorGrouping {

		private final DeferredImportSelector.Group group;

		private final List<DeferredImportSelectorHolder> deferredImports = new ArrayList<>();

		DeferredImportSelectorGrouping(Group group) {
			this.group = group;
		}

		public void add(DeferredImportSelectorHolder deferredImport) {
			this.deferredImports.add(deferredImport);
		}

		
Return the imports defined by the group.

Returns:each import with its associated configuration class
/**
		 * Return the imports defined by the group.
		 * @return each import with its associated configuration class
		 */
		public Iterable<Group.Entry> getImports() {
			for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {
				this.group.process(deferredImport.getConfigurationClass().getMetadata(),
						deferredImport.getImportSelector());
			}
			return this.group.selectImports();
		}
	}


	private static class DefaultDeferredImportSelectorGroup implements Group {

		private final List<Entry> imports = new ArrayList<>();

		@Override
		public void process(AnnotationMetadata metadata, DeferredImportSelector selector) {
			for (String importClassName : selector.selectImports(metadata)) {
				this.imports.add(new Entry(metadata, importClassName));
			}
		}

		@Override
		public Iterable<Entry> selectImports() {
			return this.imports;
		}
	}


	
Simple wrapper that allows annotated source classes to be dealt with
in a uniform manner, regardless of how they are loaded.

/**
	 * Simple wrapper that allows annotated source classes to be dealt with
	 * in a uniform manner, regardless of how they are loaded.
	 */
	private class SourceClass implements Ordered {

		private final Object source;  // Class or MetadataReader

		private final AnnotationMetadata metadata;

		public SourceClass(Object source) {
			this.source = source;
			if (source instanceof Class) {
				this.metadata = new StandardAnnotationMetadata((Class<?>) source, true);
			}
			else {
				this.metadata = ((MetadataReader) source).getAnnotationMetadata();
			}
		}

		public final AnnotationMetadata getMetadata() {
			return this.metadata;
		}

		@Override
		public int getOrder() {
			Integer order = ConfigurationClassUtils.getOrder(this.metadata);
			return (order != null ? order : Ordered.LOWEST_PRECEDENCE);
		}

		public Class<?> loadClass() throws ClassNotFoundException {
			if (this.source instanceof Class) {
				return (Class<?>) this.source;
			}
			String className = ((MetadataReader) this.source).getClassMetadata().getClassName();
			return ClassUtils.forName(className, resourceLoader.getClassLoader());
		}

		public boolean isAssignable(Class<?> clazz) throws IOException {
			if (this.source instanceof Class) {
				return clazz.isAssignableFrom((Class<?>) this.source);
			}
			return new AssignableTypeFilter(clazz).match((MetadataReader) this.source, metadataReaderFactory);
		}

		public ConfigurationClass asConfigClass(ConfigurationClass importedBy) throws IOException {
			if (this.source instanceof Class) {
				return new ConfigurationClass((Class<?>) this.source, importedBy);
			}
			return new ConfigurationClass((MetadataReader) this.source, importedBy);
		}

		public Collection<SourceClass> getMemberClasses() throws IOException {
			Object sourceToProcess = this.source;
			if (sourceToProcess instanceof Class) {
				Class<?> sourceClass = (Class<?>) sourceToProcess;
				try {
					Class<?>[] declaredClasses = sourceClass.getDeclaredClasses();
					List<SourceClass> members = new ArrayList<>(declaredClasses.length);
					for (Class<?> declaredClass : declaredClasses) {
						members.add(asSourceClass(declaredClass));
					}
					return members;
				}
				catch (NoClassDefFoundError err) {
					// getDeclaredClasses() failed because of non-resolvable dependencies
					// -> fall back to ASM below
					sourceToProcess = metadataReaderFactory.getMetadataReader(sourceClass.getName());
				}
			}

			// ASM-based resolution - safe for non-resolvable classes as well
			MetadataReader sourceReader = (MetadataReader) sourceToProcess;
			String[] memberClassNames = sourceReader.getClassMetadata().getMemberClassNames();
			List<SourceClass> members = new ArrayList<>(memberClassNames.length);
			for (String memberClassName : memberClassNames) {
				try {
					members.add(asSourceClass(memberClassName));
				}
				catch (IOException ex) {
					// Let's skip it if it's not resolvable - we're just looking for candidates
					if (logger.isDebugEnabled()) {
						logger.debug("Failed to resolve member class [" + memberClassName +
								"] - not considering it as a configuration class candidate");
					}
				}
			}
			return members;
		}

		public SourceClass getSuperClass() throws IOException {
			if (this.source instanceof Class) {
				return asSourceClass(((Class<?>) this.source).getSuperclass());
			}
			return asSourceClass(((MetadataReader) this.source).getClassMetadata().getSuperClassName());
		}

		public Set<SourceClass> getInterfaces() throws IOException {
			Set<SourceClass> result = new LinkedHashSet<>();
			if (this.source instanceof Class) {
				Class<?> sourceClass = (Class<?>) this.source;
				for (Class<?> ifcClass : sourceClass.getInterfaces()) {
					result.add(asSourceClass(ifcClass));
				}
			}
			else {
				for (String className : this.metadata.getInterfaceNames()) {
					result.add(asSourceClass(className));
				}
			}
			return result;
		}

		public Set<SourceClass> getAnnotations() throws IOException {
			Set<SourceClass> result = new LinkedHashSet<>();
			for (String className : this.metadata.getAnnotationTypes()) {
				try {
					result.add(getRelated(className));
				}
				catch (Throwable ex) {
					// An annotation not present on the classpath is being ignored
					// by the JVM's class loading -> ignore here as well.
				}
			}
			return result;
		}

		public Collection<SourceClass> getAnnotationAttributes(String annType, String attribute) throws IOException {
			Map<String, Object> annotationAttributes = this.metadata.getAnnotationAttributes(annType, true);
			if (annotationAttributes == null || !annotationAttributes.containsKey(attribute)) {
				return Collections.emptySet();
			}
			String[] classNames = (String[]) annotationAttributes.get(attribute);
			Set<SourceClass> result = new LinkedHashSet<>();
			for (String className : classNames) {
				result.add(getRelated(className));
			}
			return result;
		}

		private SourceClass getRelated(String className) throws IOException {
			if (this.source instanceof Class) {
				try {
					Class<?> clazz = ClassUtils.forName(className, ((Class<?>) this.source).getClassLoader());
					return asSourceClass(clazz);
				}
				catch (ClassNotFoundException ex) {
					// Ignore -> fall back to ASM next, except for core java types.
					if (className.startsWith("java")) {
						throw new NestedIOException("Failed to load class [" + className + "]", ex);
					}
					return new SourceClass(metadataReaderFactory.getMetadataReader(className));
				}
			}
			return asSourceClass(className);
		}

		@Override
		public boolean equals(Object other) {
			return (this == other || (other instanceof SourceClass &&
					this.metadata.getClassName().equals(((SourceClass) other).metadata.getClassName())));
		}

		@Override
		public int hashCode() {
			return this.metadata.getClassName().hashCode();
		}

		@Override
		public String toString() {
			return this.metadata.getClassName();
		}
	}


	
Problem registered upon detection of a circular Import. 
/**
	 * {@link Problem} registered upon detection of a circular {@link Import}.
	 */
	private static class CircularImportProblem extends Problem {

		public CircularImportProblem(ConfigurationClass attemptedImport, Deque<ConfigurationClass> importStack) {
			super(String.format("A circular @Import has been detected: " +
					"Illegal attempt by @Configuration class '%s' to import class '%s' as '%s' is " +
					"already present in the current import stack %s", importStack.element().getSimpleName(),
					attemptedImport.getSimpleName(), attemptedImport.getSimpleName(), importStack),
					new Location(importStack.element().getResource(), attemptedImport.getMetadata()));
		}
	}

}