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一、Spring生命周期核心底层源码剖析—扫描

1.1、Spring底层扫描机制doScan方法源码剖析

其源代码如下：

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {Assert.notEmpty(basePackages, "At least one base package must be specified");Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();for (String basePackage : basePackages) {Set<BeanDefinition> candidates = findCandidateComponents(basePackage);//遍历其获取到的BeanDefinition对象for (BeanDefinition candidate : candidates) {//为其BeanDefinition对象进行属性赋值，例如scope，beanName等ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);candidate.setScope(scopeMetadata.getScopeName());String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);if (candidate instanceof AbstractBeanDefinition) {postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);}if (candidate instanceof AnnotatedBeanDefinition) {AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);}//判断当前的bean是否已经在Spring容器中存在，存在需封装为BeanDefinitionHolder对象if (checkCandidate(beanName, candidate)) {BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);definitionHolder =AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);beanDefinitions.add(definitionHolder);registerBeanDefinition(definitionHolder, this.registry);}}}return beanDefinitions;}

1、其主要是通过传入的包路径进行资源加载，加载时方法为上诉代码的for循环下的第一行代码的findCandidateComponents()方法，可以详细看此方法，是如何加载资源的，其方法代码如下（具体说明以及解析过程可参考注释）：

public Set<BeanDefinition> findCandidateComponents(String basePackage) {//此处主要是判断项目是否配置了相关的bean文件，若有，就不需要再逐个类进行扫描+判断是否为Beanif (this.componentsIndex != null && indexSupportsIncludeFilters()) {return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);}//大部分的业务都会走如下方法else {return scanCandidateComponents(basePackage);}}//scanCandidateComponents方法具体实现为
private Set<BeanDefinition> scanCandidateComponents(String basePackage) {Set<BeanDefinition> candidates = new LinkedHashSet<>();try {//1、资源路径组装解析String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +resolveBasePackage(basePackage) + '/' + this.resourcePattern;//2、利用类元数据读取器读取器路径下包含的资源数据Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);boolean traceEnabled = logger.isTraceEnabled();boolean debugEnabled = logger.isDebugEnabled();//3、遍历类元数据读取器获取到的资源数据（class资源文件数据）for (Resource resource : resources) {if (traceEnabled) {logger.trace("Scanning " + resource);}try {//4、获取当前类元数据(calss)具体资源信息MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);//5、判断当前的类（class）上包含的是否包含排除注解excludeFilters以及非排除注解includeFilters，以及是否包含相关的条件注解Conditionalif (isCandidateComponent(metadataReader)) {//6、创建一个BeanDefinition对象，用于封装其类特征信息，例如：beanClass、scope、lazyInit等属性ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);//7、将类资源数据加入到BeanDefinition中sbd.setSource(resource);//8、判断当前的类资源是否是独立的（例如是否是内部类等），除此歪，需要判断其是否为接口或者抽象类，如果是抽象类，那类中必须有被Lookup注解的方法，否则不会被当做beanif (isCandidateComponent(sbd)) {if (debugEnabled) {logger.debug("Identified candidate component class: " + resource);}//9、将封装好的BeanDefinition对象加入到返回的集合Set中candidates.add(sbd);}else {if (debugEnabled) {logger.debug("Ignored because not a concrete top-level class: " + resource);}}}else {if (traceEnabled) {logger.trace("Ignored because not matching any filter: " + resource);}}}catch (FileNotFoundException ex) {if (traceEnabled) {logger.trace("Ignored non-readable " + resource + ": " + ex.getMessage());}}catch (Throwable ex) {throw new BeanDefinitionStoreException("Failed to read candidate component class: " + resource, ex);}}}catch (IOException ex) {throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);}return candidates;}