Spring @ComponentScan注解扫描组件原理
xuguofeng2016 人气:0本文将通过阅读spring源码,分析@ComponentScan注解扫描组件的原理。
和@Bean注解一样,@ComponentScan注解也是通过ConfigurationClassPostProcessor后置处理器完成扫描工作的。
在《Spring-@Bean注解源码分析》中,详细介绍了spring注册、调用ConfigurationClassPostProcessor后置处理器的流程,本文不再重复记录。
ConfigurationClassPostProcessor类
ConfigurationClassPostProcessor实现了BeanDefinitionRegistryPostProcessor接口,spring容器在refresh过程中,会调用所有BeanDefinitionRegistryPostProcessor处理器的postProcessBeanDefinitionRegistry方法:
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) { processConfigBeanDefinitions(registry); } public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { // ... // Parse each @Configuration class ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates); Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size()); do { parser.parse(candidates); parser.validate(); Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses()); configClasses.removeAll(alreadyParsed); // Read the model and create bean definitions based on its content if (this.reader == null) { this.reader = new ConfigurationClassBeanDefinitionReader( registry, this.sourceExtractor, this.resourceLoader, this.environment, this.importBeanNameGenerator, parser.getImportRegistry()); } this.reader.loadBeanDefinitions(configClasses); // ...
重点逻辑在parser.parse(candidates)处,作用是解析@Configuration类。
Parse each @Configuration class
parser.parse(candidates);
最终调用到:
protected final SourceClass doProcessConfigurationClass( ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter) throws IOException { // ... // 1. 解析@ComponentScan注解元数据 Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable( sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class); // 2. 判断标注了@ComponentScan注解且不skip该类 if (!componentScans.isEmpty() && !this.conditionEvaluator.shouldSkip( sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) { // 可能标注多个@ComponentScan注解 for (AnnotationAttributes componentScan : componentScans) { // 3. 通过@ComponentScan解析组件BeanDefinition集 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 // 4. 递归解析 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()); } } } } // ... }
重点在第3点,通过@ComponentScan解析组件BeanDefinition集:
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
componentScanParser是ComponentScanAnnotationParser类型对象,parse方法解析ComponentScan注解,扫描组件。
ComponentScanAnnotationParser类
parse方法解析ComponentScan注解,扫描组件:
public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) { ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry, componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader); Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator"); boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass); scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator : BeanUtils.instantiateClass(generatorClass)); ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy"); if (scopedProxyMode != ScopedProxyMode.DEFAULT) { scanner.setScopedProxyMode(scopedProxyMode); } else { Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver"); scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass)); } scanner.setResourcePattern(componentScan.getString("resourcePattern")); for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) { for (TypeFilter typeFilter : typeFiltersFor(filter)) { scanner.addIncludeFilter(typeFilter); } } for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) { for (TypeFilter typeFilter : typeFiltersFor(filter)) { scanner.addExcludeFilter(typeFilter); } } boolean lazyInit = componentScan.getBoolean("lazyInit"); if (lazyInit) { scanner.getBeanDefinitionDefaults().setLazyInit(true); } Set<String> basePackages = new LinkedHashSet<>(); String[] basePackagesArray = componentScan.getStringArray("basePackages"); for (String pkg : basePackagesArray) { String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg), ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); Collections.addAll(basePackages, tokenized); } for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) { basePackages.add(ClassUtils.getPackageName(clazz)); } if (basePackages.isEmpty()) { basePackages.add(ClassUtils.getPackageName(declaringClass)); } scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) { @Override protected boolean matchClassName(String className) { return declaringClass.equals(className); } }); return scanner.doScan(StringUtils.toStringArray(basePackages)); }
ClassPathBeanDefinitionScanner类
doScan方法扫描指定包下面的组件:
protected Set<BeanDefinitionHolder> doScan(String... basePackages) { Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>(); for (String basePackage : basePackages) { // 扫描组件 Set<BeanDefinition> candidates = findCandidateComponents(basePackage); for (BeanDefinition candidate : candidates) { 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); } if (checkCandidate(beanName, candidate)) { BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName); definitionHolder = AnnotationConfigUtils .applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); beanDefinitions.add(definitionHolder); // 注册到容器 registerBeanDefinition(definitionHolder, this.registry); } } } return beanDefinitions; } public Set<BeanDefinition> findCandidateComponents(String basePackage) { if (this.componentsIndex != null && indexSupportsIncludeFilters()) { return addCandidateComponentsFromIndex(this.componentsIndex, basePackage); } else { return scanCandidateComponents(basePackage); } } private Set<BeanDefinition> scanCandidateComponents(String basePackage) { Set<BeanDefinition> candidates = new LinkedHashSet<>(); try { String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + resolveBasePackage(basePackage) + '/' + this.resourcePattern; Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath); for (Resource resource : resources) { if (resource.isReadable()) { try { MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource); // 判断是否是需要扫描的spring组件,遍历excludeFilters和includeFilters集来进行判断 if (isCandidateComponent(metadataReader)) { ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader); sbd.setSource(resource); if (isCandidateComponent(sbd)) { candidates.add(sbd); } } } catch (Throwable ex) { throw new BeanDefinitionStoreException(""); } } } } catch (IOException ex) { throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex); } return candidates; }
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