Spring组件扫描原理解析一、概述用一幅图来对两种方式配置Bean的组件扫描进行一个总结二、原理剖析通过之前的学习我们知道只要是将Bean放到了BeanDefinitionMap中那么就势必会经过Spring的那套Bean的生命周期就势必会创建Bean。2.1xml组件扫描方式首先我们在xml中是通过这段代码来进行组件扫描的扫描指定的基本包及其子包下的类识别使用Component注解context:component-scan base-packagecom.itheima/依据之前学习的命名空间的知识我们知道通过命名空间是可以找到它对应的Handler处理器的命名空间xmlns:contexthttp://www.springframework.org/schema/context对应的Handler处理器http\://www.springframework.org/schema/contextorg.springframework.context.config.ContextNamespaceHandlerhttp\://www.springframework.org/schema/jeeorg.springframework.ejb.config.JeeNamespaceHandlerhttp\://www.springframework.org/schema/langorg.springframework.scripting.config.LangNamespaceHandlerhttp\://www.springframework.org/schema/taskorg.springframework.scheduling.config.TaskNamespaceHandlerhttp\://www.springframework.org/schema/cacheorg.springframework.cache.config.CacheNamespaceHandler进入ContextNamespaceHandler//// Source code recreated from a .class file by IntelliJ IDEA// (powered by FernFlower decompiler)//packageorg.springframework.context.config;importorg.springframework.beans.factory.xml.NamespaceHandlerSupport;importorg.springframework.context.annotation.AnnotationConfigBeanDefinitionParser;importorg.springframework.context.annotation.ComponentScanBeanDefinitionParser;publicclassContextNamespaceHandlerextendsNamespaceHandlerSupport{publicContextNamespaceHandler(){}publicvoidinit(){this.registerBeanDefinitionParser(property-placeholder,newPropertyPlaceholderBeanDefinitionParser());this.registerBeanDefinitionParser(property-override,newPropertyOverrideBeanDefinitionParser());this.registerBeanDefinitionParser(annotation-config,newAnnotationConfigBeanDefinitionParser());this.registerBeanDefinitionParser(component-scan,newComponentScanBeanDefinitionParser());this.registerBeanDefinitionParser(load-time-weaver,newLoadTimeWeaverBeanDefinitionParser());this.registerBeanDefinitionParser(spring-configured,newSpringConfiguredBeanDefinitionParser());this.registerBeanDefinitionParser(mbean-export,newMBeanExportBeanDefinitionParser());this.registerBeanDefinitionParser(mbean-server,newMBeanServerBeanDefinitionParser());}}进入component-scan对应的ComponentScanBeanDefinitionParser看它的parse解析方法NullablepublicBeanDefinitionparse(Elementelement,ParserContextparserContext){StringbasePackageelement.getAttribute(base-package);basePackageparserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);String[]basePackagesStringUtils.tokenizeToStringArray(basePackage,,; \t\n);ClassPathBeanDefinitionScannerscannerthis.configureScanner(parserContext,element);SetBeanDefinitionHolderbeanDefinitionsscanner.doScan(basePackages);this.registerComponents(parserContext.getReaderContext(),beanDefinitions,element);returnnull;}进入ClassPathBeanDefinitionScanner的doScan方法重点看这if(this.checkCandidate(beanName,candidate)){BeanDefinitionHolderdefinitionHoldernewBeanDefinitionHolder(candidate,beanName);definitionHolderAnnotationConfigUtils.applyScopedProxyMode(scopeMetadata,definitionHolder,this.registry);beanDefinitions.add(definitionHolder);this.registerBeanDefinition(definitionHolder,this.registry);}执行到BeanDefinitionHolder definitionHolder new BeanDefinitionHolder(candidate, beanName);时可以看到BeanName是OtherBean3BeanDefinitionMap为空执行完this.registerBeanDefinition(definitionHolder, this.registry);OtherBean3就注入了BeanDefinitionMap由此可见xml组件扫描方式是将Bean直接放到BeanDefinitionMap中实现创建Bean的并没有通过BeanFactoryPostProcessor。2.2注解方式主键扫描首先先是进入AnnotationConfigApplicationContext类publicclassAnnotationConfigApplicationContextextendsGenericApplicationContextimplementsAnnotationConfigRegistry{privatefinalAnnotatedBeanDefinitionReaderreader;privatefinalClassPathBeanDefinitionScannerscanner;publicAnnotationConfigApplicationContext(){StartupStepcreateAnnotatedBeanDefReaderthis.getApplicationStartup().start(spring.context.annotated-bean-reader.create);this.readernewAnnotatedBeanDefinitionReader(this);createAnnotatedBeanDefReader.end();this.scannernewClassPathBeanDefinitionScanner(this);}publicAnnotationConfigApplicationContext(DefaultListableBeanFactorybeanFactory){super(beanFactory);this.readernewAnnotatedBeanDefinitionReader(this);this.scannernewClassPathBeanDefinitionScanner(this);}publicAnnotationConfigApplicationContext(Class?...componentClasses){this();this.register(componentClasses);this.refresh();}publicAnnotationConfigApplicationContext(String...basePackages){this();this.scan(basePackages);this.refresh();}直接进入this()publicAnnotationConfigApplicationContext(){StartupStepcreateAnnotatedBeanDefReaderthis.getApplicationStartup().start(spring.context.annotated-bean-reader.create);this.readernewAnnotatedBeanDefinitionReader(this);createAnnotatedBeanDefReader.end();this.scannernewClassPathBeanDefinitionScanner(this);}进入AnnotatedBeanDefinitionReader之前xml的形式是XmlBeanDefinitionReaderpublicAnnotatedBeanDefinitionReader(BeanDefinitionRegistryregistry){this(registry,getOrCreateEnvironment(registry));}publicAnnotatedBeanDefinitionReader(BeanDefinitionRegistryregistry,Environmentenvironment){this.beanNameGeneratorAnnotationBeanNameGenerator.INSTANCE;this.scopeMetadataResolvernewAnnotationScopeMetadataResolver();Assert.notNull(registry,BeanDefinitionRegistry must not be null);Assert.notNull(environment,Environment must not be null);this.registryregistry;this.conditionEvaluatornewConditionEvaluator(registry,environment,(ResourceLoader)null);AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);}再是进入**AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);**中的registerAnnotationConfigProcessorspublicstaticSetBeanDefinitionHolderregisterAnnotationConfigProcessors(BeanDefinitionRegistryregistry,NullableObjectsource){DefaultListableBeanFactorybeanFactoryunwrapDefaultListableBeanFactory(registry);if(beanFactory!null){if(!(beanFactory.getDependencyComparator()instanceofAnnotationAwareOrderComparator)){beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);}if(!(beanFactory.getAutowireCandidateResolver()instanceofContextAnnotationAutowireCandidateResolver)){beanFactory.setAutowireCandidateResolver(newContextAnnotationAutowireCandidateResolver());}}SetBeanDefinitionHolderbeanDefsnewLinkedHashSet(8);if(!registry.containsBeanDefinition(org.springframework.context.annotation.internalConfigurationAnnotationProcessor)){RootBeanDefinitiondefnewRootBeanDefinition(ConfigurationClassPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry,def,org.springframework.context.annotation.internalConfigurationAnnotationProcessor));}if(!registry.containsBeanDefinition(org.springframework.context.annotation.internalAutowiredAnnotationProcessor)){RootBeanDefinitiondefnewRootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry,def,org.springframework.context.annotation.internalAutowiredAnnotationProcessor));}if(jsr250Present!registry.containsBeanDefinition(org.springframework.context.annotation.internalCommonAnnotationProcessor)){RootBeanDefinitiondefnewRootBeanDefinition(CommonAnnotationBeanPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry,def,org.springframework.context.annotation.internalCommonAnnotationProcessor));}if(jpaPresent!registry.containsBeanDefinition(org.springframework.context.annotation.internalPersistenceAnnotationProcessor)){RootBeanDefinitiondefnewRootBeanDefinition();try{def.setBeanClass(ClassUtils.forName(org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor,AnnotationConfigUtils.class.getClassLoader()));}catch(ClassNotFoundExceptionex){thrownewIllegalStateException(Cannot load optional framework class: org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor,ex);}def.setSource(source);beanDefs.add(registerPostProcessor(registry,def,org.springframework.context.annotation.internalPersistenceAnnotationProcessor));}if(!registry.containsBeanDefinition(org.springframework.context.event.internalEventListenerProcessor)){RootBeanDefinitiondefnewRootBeanDefinition(EventListenerMethodProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry,def,org.springframework.context.event.internalEventListenerProcessor));}if(!registry.containsBeanDefinition(org.springframework.context.event.internalEventListenerFactory)){RootBeanDefinitiondefnewRootBeanDefinition(DefaultEventListenerFactory.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry,def,org.springframework.context.event.internalEventListenerFactory));}returnbeanDefs;}在这里会注册六个if中的Bean进入BeanDefinitionMap当中每执行完一次return beanDefs就是注册一个。再进入ConfigurationClassPostProcessor.class因为是注解形式的组件扫描看到postProcessBeanDefinitionRegistry中的parser.parse(candidates);的parse方法关注与parse相关的for(BeanDefinitionHolderholder:this.componentScanParser.parse(componentScan,sourceClass.getMetadata().getClassName())){继续推进看componentScanParser的parse方法ClassPathBeanDefinitionScannerscannernewClassPathBeanDefinitionScanner(this.registry,componentScan.getBoolean(useDefaultFilters),this.environment,this.resourceLoader);是否有一种似曾相识燕归来的感觉呢哈哈实际上这是和xml配置组件扫描是一致的啦接下来就是老套路了继续看doscan由此进入returnscanner.doScan(StringUtils.toStringArray(basePackages));if(this.checkCandidate(beanName,candidate)){BeanDefinitionHolderdefinitionHoldernewBeanDefinitionHolder(candidate,beanName);definitionHolderAnnotationConfigUtils.applyScopedProxyMode(scopeMetadata,definitionHolder,this.registry);beanDefinitions.add(definitionHolder);this.registerBeanDefinition(definitionHolder,this.registry);一样的逻辑定义definitionHolder使用BeanDefinitionRegistry的registerBeanDefinition(definitionHolder进行注册Bean到BeanDefinitionMap当中完结了。