spring源码分析之@ImportSelector、@Import、ImportResource工作原理分析

2024-04-08 12:48
文章标签 java 分析 源码 工作 spring 原理 import importresource importselector

本文主要是介绍spring源码分析之@ImportSelector、@Import、ImportResource工作原理分析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1. @importSelector定义：

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/*** Interface to be implemented by types that determine which @{@link Configuration}* class(es) should be imported based on a given selection criteria, usually one or more* annotation attributes.** <p>An {@link ImportSelector} may implement any of the following* {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective* methods will be called prior to {@link #selectImports}:* <ul>* <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>* <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}</li>* <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}</li>* <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}</li>* </ul>** <p>ImportSelectors are usually processed in the same way as regular {@code @Import}* annotations, however, it is also possible to defer selection of imports until all* {@code @Configuration} classes have been processed (see {@link DeferredImportSelector}* for details).** @author Chris Beams* @since 3.1* @see DeferredImportSelector* @see Import* @see ImportBeanDefinitionRegistrar* @see Configuration*/
public interface ImportSelector {/*** Select and return the names of which class(es) should be imported based on* the {@link AnnotationMetadata} of the importing @{@link Configuration} class.*/String[] selectImports(AnnotationMetadata importingClassMetadata);}
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实现线索：

具体代码实现：

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    private void processDeferredImportSelectors() {List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;this.deferredImportSelectors = null;Collections.sort(deferredImports, DEFERRED_IMPORT_COMPARATOR);for (DeferredImportSelectorHolder deferredImport : deferredImports) {ConfigurationClass configClass = deferredImport.getConfigurationClass();try {String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());processImports(configClass, asSourceClass(configClass), asSourceClasses(imports), false);}catch (BeanDefinitionStoreException ex) {throw ex;}catch (Throwable ex) {throw new BeanDefinitionStoreException("Failed to process import candidates for configuration class [" +configClass.getMetadata().getClassName() + "]", ex);}}}
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2、@Import和@ImportResource的实现如下：

ConfigurationClassParser.java

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/*** 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*/protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {// Recursively process any member (nested) classes first
        processMemberClasses(configClass, sourceClass);// Process any @PropertySource annotationsfor (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(sourceClass.getMetadata(), PropertySources.class, org.springframework.context.annotation.PropertySource.class)) {if (this.environment instanceof ConfigurableEnvironment) {processPropertySource(propertySource);}else {logger.warn("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 immediatelySet<BeanDefinitionHolder> scannedBeanDefinitions =this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());// Check the set of scanned definitions for any further config classes and parse recursively if necessaryfor (BeanDefinitionHolder holder : scannedBeanDefinitions) {if (ConfigurationClassUtils.checkConfigurationClassCandidate(holder.getBeanDefinition(), this.metadataReaderFactory)) {parse(holder.getBeanDefinition().getBeanClassName(), holder.getBeanName());}}}}// Process any @Import annotationsprocessImports(configClass, sourceClass, getImports(sourceClass), true);// Process any @ImportResource annotationsif (sourceClass.getMetadata().isAnnotated(ImportResource.class.getName())) {AnnotationAttributes importResource =AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);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 methodsSet<MethodMetadata> beanMethods = sourceClass.getMetadata().getAnnotatedMethods(Bean.class.getName());for (MethodMetadata methodMetadata : beanMethods) {configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));}// Process default methods on interfaces
        processInterfaces(configClass, sourceClass);// Process superclass, if anyif (sourceClass.getMetadata().hasSuperClass()) {String superclass = sourceClass.getMetadata().getSuperClassName();if (!superclass.startsWith("java") && !this.knownSuperclasses.containsKey(superclass)) {this.knownSuperclasses.put(superclass, configClass);// Superclass found, return its annotation metadata and recursereturn sourceClass.getSuperClass();}}// No superclass -> processing is completereturn null;}
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 3.三种方式：

ImportSelector 
ImportBeanDefinitionRegistrar 
Configuration

ConfigurationClassParser.java

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private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,Collection<SourceClass> importCandidates, boolean checkForCircularImports) throws IOException {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 importsClass<?> candidateClass = candidate.loadClass();ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);ParserStrategyUtils.invokeAwareMethods(selector, this.environment, this.resourceLoader, this.registry);if (this.deferredImportSelectors != null && selector instanceof DeferredImportSelector) {this.deferredImportSelectors.add(new DeferredImportSelectorHolder(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 definitionsClass<?> 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 classthis.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();}}}

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