Spring Boot启动过程中的后置处理
在前一篇博文Spring Boot启动流程分析的调用 beanFactory 的后置处理小节中提到了beanFactory的后置处理。这部分是Spring IoC的重点，但是因为内容很长，所以在这里单独开一篇博文来分析。
调用beanFactoryPostProcessors
话不多说，继续从AbstractApplicationContext#refresh调用invokeBeanFactoryPostProcessors方法这里开始。
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// 重点
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
if (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null &&
beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
// PostProcessorRegistrationDelegate
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// WARNING: Although it may appear that the body of this method can be easily
// refactored to avoid the use of multiple loops and multiple lists, the use
// of multiple lists and multiple passes over the names of processors is
// intentional. We must ensure that we honor the contracts for PriorityOrdered
// and Ordered processors. Specifically, we must NOT cause processors to be
// instantiated (via getBean() invocations) or registered in the ApplicationContext
// in the wrong order.
//
// Before submitting a pull request (PR) to change this method, please review the
// list of all declined PRs involving changes to PostProcessorRegistrationDelegate
// to ensure that your proposal does not result in a breaking change:
// https://github.com/spring-projects/spring-framework/issues?q=PostProcessorRegistrationDelegate+is%3Aclosed+label%3A%22status%3A+declined%22
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
if (beanFactory instanceof BeanDefinitionRegistry registry) {
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor registryProcessor) {
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// Separate between BeanDefinitionRegistryPostProcessors that implement
// PriorityOrdered, Ordered, and the rest.
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
// 这里是重点
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
beanFactory.clearMetadataCache();
}
这一大段代码，实话说看得我云里雾里的，但站在巨人的肩膀上之后，我大概明白invokeBeanDefinitionRegistryPostProcessors这个方法调用是里面的重点，那接下来就随着巨人的指引看看这个方法。
private static void invokeBeanDefinitionRegistryPostProcessors(
Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {
for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
.tag("postProcessor", postProcessor::toString);
postProcessor.postProcessBeanDefinitionRegistry(registry);
postProcessBeanDefRegistry.end();
}
}
debug到postProcessBeanDefinitionRegistry这一行，发现postProcessors里面只有ConfigurationClassPostProcessor，那么就进去看看这个类的postProcessBeanDefinitionRegistry在干什么。
下面代码会大量提到configuration class这个概念，而所谓configuration class，就是带有@Configuration或者@Component注解的类。
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
int registryId = System.identityHashCode(registry);
if (this.registriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);
}
if (this.factoriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + registry);
}
this.registriesPostProcessed.add(registryId);
processConfigBeanDefinitions(registry);
}
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();
// 遍历所有的bean definition的名字
for (String beanName : candidateNames) {
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) {
if (logger.isDebugEnabled()) {
logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
}
}
// 检查这个bean definition是不是一个配置类
// 1. 取得bean definition的metadata
// 2. 设定configurationClass这个bean definition attribute的值，full或lite（暂不清楚是干什么用的）
// 3. 如果指定了这个配置类的生效顺序，那么将其记录到order这个attribute中
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
// Return immediately if no @Configuration classes were found
if (configCandidates.isEmpty()) {
return;
}
// Sort by previously determined @Order value, if applicable
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
// Detect any custom bean name generation strategy supplied through the enclosing application context
SingletonBeanRegistry sbr = null;
if (registry instanceof SingletonBeanRegistry _sbr) {
sbr = _sbr;
if (!this.localBeanNameGeneratorSet) {
BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(
AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR);
if (generator != null) {
this.componentScanBeanNameGenerator = generator;
this.importBeanNameGenerator = generator;
}
}
}
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// 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 {
StartupStep processConfig = this.applicationStartup.start("spring.context.config-classes.parse");
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);
alreadyParsed.addAll(configClasses);
processConfig.tag("classCount", () -> String.valueOf(configClasses.size())).end();
candidates.clear();
if (registry.getBeanDefinitionCount() > candidateNames.length) {
String[] newCandidateNames = registry.getBeanDefinitionNames();
Set<String> oldCandidateNames = Set.of(candidateNames);
Set<String> alreadyParsedClasses = new HashSet<>();
for (ConfigurationClass configurationClass : alreadyParsed) {
alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());
}
for (String candidateName : newCandidateNames) {
if (!oldCandidateNames.contains(candidateName)) {
BeanDefinition bd = registry.getBeanDefinition(candidateName);
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
!alreadyParsedClasses.contains(bd.getBeanClassName())) {
candidates.add(new BeanDefinitionHolder(bd, candidateName));
}
}
}
candidateNames = newCandidateNames;
}
}
while (!candidates.isEmpty());
// Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes
if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
}
// Store the PropertySourceDescriptors to contribute them Ahead-of-time if necessary
this.propertySourceDescriptors = parser.getPropertySourceDescriptors();
if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory cachingMetadataReaderFactory) {
// Clear cache in externally provided MetadataReaderFactory; this is a no-op
// for a shared cache since it'll be cleared by the ApplicationContext.
cachingMetadataReaderFactory.clearCache();
}
}
首先这里会遍历所有的bean definition，找到其中的配置类，然后调用parse方法解析它们。
public void parse(Set<BeanDefinitionHolder> configCandidates) {
for (BeanDefinitionHolder holder : configCandidates) {
BeanDefinition bd = holder.getBeanDefinition();
try {
// 如果是从Spring Boot项目进来的，那么这里的bd就是主类封装成的AnnotatedGenericBeanDefinition
if (bd instanceof AnnotatedBeanDefinition annotatedBeanDef) {
parse(annotatedBeanDef.getMetadata(), holder.getBeanName());
}
else if (bd instanceof AbstractBeanDefinition abstractBeanDef && abstractBeanDef.hasBeanClass()) {
parse(abstractBeanDef.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);
}
}
// 加载默认的配置，即自动装配的入口
this.deferredImportSelectorHandler.process();
}
protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {
processConfigurationClass(new ConfigurationClass(metadata, beanName), DEFAULT_EXCLUSION_FILTER);
}
protected void processConfigurationClass(ConfigurationClass configClass, Predicate<String> filter) 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.
// 递归处理当前的configuration class及其父类
SourceClass sourceClass = null;
try {
sourceClass = asSourceClass(configClass, filter);
do {
sourceClass = doProcessConfigurationClass(configClass, sourceClass, filter);
}
while (sourceClass != null);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"I/O failure while processing configuration class [" + sourceClass + "]", ex);
}
this.configurationClasses.put(configClass, configClass);
}
// ConfigurationClassParser
@Nullable
protected final SourceClass doProcessConfigurationClass(
ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
throws IOException {
// 如果这个configuration class带有@Component注解
// 那么就递归处理其内部类
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass, filter);
}
// Process any @PropertySource annotations
// 针对@PropertySource注解的处理
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), org.springframework.context.annotation.PropertySource.class,
PropertySources.class, true)) {
if (this.propertySourceRegistry != null) {
this.propertySourceRegistry.processPropertySource(propertySource);
}
else {
logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
"]. Reason: Environment must implement ConfigurableEnvironment");
}
}
// Search for locally declared @ComponentScan annotations first.
// 根据@ComponentScan注解扫描项目中的bean
Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), ComponentScan.class, ComponentScans.class,
MergedAnnotation::isDirectlyPresent);
// Fall back to searching for @ComponentScan meta-annotations (which indirectly
// includes locally declared composed annotations).
// 如果没找到直接使用的@ComponentScan注解，那么就尝试找间接的引用
// 如 @SpringBootApplication -> @ComponentScan
if (componentScans.isEmpty()) {
componentScans = AnnotationConfigUtils.attributesForRepeatable(sourceClass.getMetadata(),
ComponentScan.class, ComponentScans.class, MergedAnnotation::isMetaPresent);
}
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
// 在这里立即开始扫描
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();
}
// 检查扫描到的这个bean是不是一个configuration class
// 如果是，那么递归查找与它关脸的configuration class，如@Bean定义的bean，或带有@Import注解的@Component类
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
// Process any @Import annotations
// 递归处理@Import注解
processImports(configClass, sourceClass, getImports(sourceClass), filter, 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
// 处理带有@Bean的方法
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;
}
Resource定位
这里的重点是Set<BeanDefinitionHolder> scannedBeanDefinitions = this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());这个方法调用，它负责处理扫描的具体过程，所以点进parse方法看它干了什么。
public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, String declaringClass) {
// 取得扫描器，并设置它的各个属性
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 includeFilterAttributes : componentScan.getAnnotationArray("includeFilters")) {
List<TypeFilter> typeFilters = TypeFilterUtils.createTypeFiltersFor(includeFilterAttributes, this.environment,
this.resourceLoader, this.registry);
for (TypeFilter typeFilter : typeFilters) {
scanner.addIncludeFilter(typeFilter);
}
}
for (AnnotationAttributes excludeFilterAttributes : componentScan.getAnnotationArray("excludeFilters")) {
List<TypeFilter> typeFilters = TypeFilterUtils.createTypeFiltersFor(excludeFilterAttributes, this.environment,
this.resourceLoader, this.registry);
for (TypeFilter typeFilter : typeFilters) {
scanner.addExcludeFilter(typeFilter);
}
}
boolean lazyInit = componentScan.getBoolean("lazyInit");
if (lazyInit) {
scanner.getBeanDefinitionDefaults().setLazyInit(true);
}
Set<String> basePackages = new LinkedHashSet<>();
// 取得basePackages的值，默认情况下为空，因为@SpringBootApplication里面就没给@ComponentScan配置这个值
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);
}
// 通过basePackageClasses里面指定的类找到它们所在的包，
// 并将其加入basePackages
// 默认情况下这个也是空的
for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
basePackages.add(ClassUtils.getPackageName(clazz));
}
// 查到最后basePackages还是空的话
// 那就把带着@ComponentScan这个注解的类所在的包加到basePackages里面
// 因为启动类带着这个注解，所以启动类所在的包就会被加进去
if (basePackages.isEmpty()) {
basePackages.add(ClassUtils.getPackageName(declaringClass));
}
scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
@Override
protected boolean matchClassName(String className) {
return declaringClass.equals(className);
}
});
// 根据basePackages扫描
return scanner.doScan(StringUtils.toStringArray(basePackages));
}
走到scanner.doScan的时候，就完成了定位这一步。接下来继续走进ClassPathBeanDefinitionScanner#doScan看它是怎么载入和注册各个BeanDefinition的。
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) {
// 从指定的包中扫描需要装载的Bean
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
// 得到这个bean的scope，如singleton、prototype等
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
// 并将其设置到BeanDefinition中
candidate.setScope(scopeMetadata.getScopeName());
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
if (candidate instanceof AbstractBeanDefinition abstractBeanDefinition) {
postProcessBeanDefinition(abstractBeanDefinition, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition annotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations(annotatedBeanDefinition);
}
// 检查与这个bean名字对应的BeanDefinition是否已经被注册过
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder =
AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
// 将这个bean注册到IoC容器
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}
BeanDefinition载入
上面代码的for循环里首先会执行findCandidateComponents，这里就是负责载入这个basePackage下的所有BeanDefinition的。
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 {
// 根据basePackages生成classpath，
// 如classpath*:com/example/demo/**/*.class
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
resolveBasePackage(basePackage) + '/' + this.resourcePattern;
// 从这个classpath下面扫描所有匹配的资源，也就是类
Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
boolean traceEnabled = logger.isTraceEnabled();
boolean debugEnabled = logger.isDebugEnabled();
// 循环处理上面找到的类，将符合条件的类包装成ScannedGenericBeanDefinition并加到candidates中
for (Resource resource : resources) {
String filename = resource.getFilename();
if (filename != null && filename.contains(ClassUtils.CGLIB_CLASS_SEPARATOR)) {
// Ignore CGLIB-generated classes in the classpath
continue;
}
if (traceEnabled) {
logger.trace("Scanning " + resource);
}
try {
MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
// 检查这个类是不是既没有命中任何一个exclude filter，并至少命中了一个include filter
// 其中一个include filter就是根据@Component注解来过滤的
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setSource(resource);
if (isCandidateComponent(sbd)) {
// 打日志，略
candidates.add(sbd);
}
else {
// 打日志，略
}
}
else {
// 打日志，略
}
}
catch (FileNotFoundException ex) {
// 打日志，略
}
catch (ClassFormatException ex) {
if (shouldIgnoreClassFormatException) {
// 打日志，略
}
else {
throw new BeanDefinitionStoreException("Incompatible class format in " + resource +
": set system property 'spring.classformat.ignore' to 'true' " +
"if you mean to ignore such files during classpath scanning", ex);
}
}
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;
}
注册BeanDefinition
回到doScan方法，在得到所有的BeanDefinition之后，就会调用registerBeanDefinition方法来完成BeanDefinition的注册。
protected void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) {
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, registry);
}
// BeanDefinitionReaderUtils
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
// 将这个bean注册到DefaultListableBeanFactory的BeanDefinitionMap
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
这里就是把传进来的BeanDefinition注册到DefaultListableBeanFactory的BeanDefinitionMap中。这部分在上一篇博文中已经提过，就不重复了。
在doScan方法的for循环遍历完所有的BeanDefinition之后，所有带有@Component注解的bean就全部注册好了。接下来会回到doProcessConfigurationClass方法，继续处理带有@Import注解的类和带有@Bean注解的方法。
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