@Configuration的基本使用和工作原理
1 基本使用
@Configuration用来标注配置类，它自身的元注解是@Component，所以能够被Spring容器管理。
它可以和其他注解联合使用，完成配置功能：
@Bean：标注方法，可以注册bean。@ComponentScan和@ComponentScans：通过ClassPathBeanDefinitionScan扫描指定路径，进行注册bean。@Import：通过引入其他配置类进行联合注册bean。@ImportResource：引入.groovy或.xml配置文件，进行注册bean。@PropertySource和@PropertySources：加载.properties文件，添加到environmen。
一个完整的@Configuration配置类使用方式如下：
@Configuration
@Order(1)
@ComponentScan
@ComponentScans(value = {@ComponentScan})
@Import(AppConfig2.class)
@ImportResource
@PropertySource("")
@PropertySources(@PropertySource(""))
public class AppConfig {
@Bean
public MyBean myBean() {
return new MyBean();
}
}
通过ApplicationContext实现类，通过注册/扫描方式将该配置类添加到容器beanDefinitionMap缓存中，@Configuration注解就可以起作用：
ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
Object myBean = context.getBean("myBean");
System.out.println(myBean);
2 工作原理
@Configuration的工作原理十分简单，它基于ApplicationContext的BeanFactoryPostProcessor机制，具体是在AbstractApplicationContext#refresh()方法invokeBeanFactoryPostProcessors()阶段，使用ConfigurationClassPostProcessor遍历容器中所有标注@Configuration的BeanDefinition缓存进行处理，包括：
- 处理注解：
@PropertySource、@ComponentScan、@ComponentScans、@Import、@ImportResource、@Bean。 - 使用
CGLIB动态代理方式增强配置类功能。 - 注册
ImportAwareBeanPostProcessor。
需要注意的是，BeanFactory并不提供BeanFactoryPostProcessor功能，如果使用底层的DefaultListableBeanFactory作为容器，不能对@Configuration进行处理。
2.1 工作流
@Configuration工作流的各个节点包括：
- 注册
ConfigurationClassPostProcessor - 执行
ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry方法 - 执行
ConfigurationClassPostProcessor#postProcessBeanFactory方法
2.1.1 注册ConfigurationClassPostProcessor
ApplicationContext实现类可以使用AnnotatedBeanDefinitionReader或ClassPathBeanDefinitionScanner读取配置类。
AnnotatedBeanDefinitionReader在在初始化时，就会注册ConfigurationClassPostProcessor：
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
this.registry = registry;
this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
ClassPathBeanDefinitionScanner在扫描路径时，默认也会注册ConfigurationClassPostProcessor：
public int scan(String... basePackages) {
int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
doScan(basePackages);
// Register annotation config processors, if necessary.
if (this.includeAnnotationConfig) {
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
}
注册的实际逻辑位于AnnotationConfigUtils#registerAnnotationConfigProcessors()：`
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
// ……省略
Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// ……省略
return beanDefs;
}
2.1.2 执行postProcessBeanDefinitionRegistry方法
ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry()中会对@PropertySource、@ComponentScan、@Import、@ImportResource和@Bean等注解进行处理。
ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry()：
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);
// 处理@PropertySource、@ComponentScan、@Import、@ImportResource和@Bean等注解
processConfigBeanDefinitions(registry);
}
2.1.3 执行postProcessBeanFactory方法
ConfigurationClassPostProcessor#postProcessBeanFactory()会使用CGLIB动态代理方式增强配置类功能，注册ImportAwareBeanPostProcessor。
如果容器不支持BeanDefinitionRegistryPostProcessor回调，那么会在这个阶段完成对@PropertySource、@ComponentScan、@Import、@ImportResource和@Bean等注解进行处理。
ConfigurationClassPostProcessor#postProcessBeanFactory()：
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
int factoryId = System.identityHashCode(beanFactory);
if (this.factoriesPostProcessed.contains(factoryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + beanFactory);
}
this.factoriesPostProcessed.add(factoryId);
if (!this.registriesPostProcessed.contains(factoryId)) {
// BeanDefinitionRegistryPostProcessor hook apparently not supported...
// Simply call processConfigurationClasses lazily at this point then.
// 处理@PropertySource、@ComponentScan、@Import、@ImportResource和@Bean等注解
processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
}
// 使用CGLIB动态代理方式增强配置类功能
enhanceConfigurationClasses(beanFactory);
// 注册ImportAwareBeanPostProcessor
beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
}
2.2 核心方法
2.2.1 注解处理
ConfigurationClassPostProcessor#processConfigBeanDefinitions()方法的工作流程：
- 遍历容器的
beanDefinitionMap，获取所有标注@Configuration注解的BeanDefinition。 - 按照
@Order进行排序。 - 解析配置类，处理
@PropertySource、@ComponentScan、@Import、@ImportResource、和@Bean等注解。
ConfigurationClassPostProcessor#processConfigBeanDefinitions()：
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
// 1、遍历容器的beanDefinitionMap，获取所有标注@Configuration注解的BeanDefinition
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();
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);
}
}
// 校验@Configuration配置类，设置CONFIGURATION_CLASS_ATTRIBUTE（来自@Configuration注解的proxyBeanMethods属性）和ORDER_ATTRIBUTE（来自@Order注解）属性
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;
}
// 2、按照@Order从小到大排序
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
// 设置beanName生成策略
SingletonBeanRegistry sbr = null;
if (registry instanceof SingletonBeanRegistry) {
sbr = (SingletonBeanRegistry) registry;
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();
}
// 3、解析配置类，处理@PropertySource、@ComponentScan、@Import、@ImportResource、和@Bean等注解
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");
// 实际解析
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());
}
// 如果扫描出新的配置类，进行注册，同时注册@Bean方法对应的bean，以及Import导入的bean
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);
processConfig.tag("classCount", () -> String.valueOf(configClasses.size())).end();
candidates.clear();
// 遍历获取新的&未处理的配置类
if (registry.getBeanDefinitionCount() > candidateNames.length) {
String[] newCandidateNames = registry.getBeanDefinitionNames();
Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(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;
}
}
// 由于可能通过扫描/引入新的配置类，需要循环对新的配置类进行解析，直到没有新的配置类
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());
}
if (this.metadataReaderFactory instanceof 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) this.metadataReaderFactory).clearCache();
}
}
通过ConfigurationClassParser#parse()处理所有标注@Configuration的BeanDefinition：
public void parse(Set<BeanDefinitionHolder> configCandidates) {
for (BeanDefinitionHolder holder : configCandidates) {
BeanDefinition bd = holder.getBeanDefinition();
try {
if (bd instanceof AnnotatedBeanDefinition) {
parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
}
else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
parse(((AbstractBeanDefinition) bd).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);
}
}
this.deferredImportSelectorHandler.process();
}
底层会调用ConfigurationClassParser#processConfigurationClass()进行处理每个配置类：
protected void processConfigurationClass(ConfigurationClass configClass, Predicate<String> filter) throws IOException {
// 根据@Conditional注解判断当前配置类是否需要注册
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.
SourceClass sourceClass = asSourceClass(configClass, filter);
do {
// 处理@PropertySource、@ComponentScan、@Import、@ImportResource、和@Bean等注解
sourceClass = doProcessConfigurationClass(configClass, sourceClass, filter);
}
while (sourceClass != null);
this.configurationClasses.put(configClass, configClass);
}
通过ConfigurationClassParser#doProcessConfigurationClass()方法处理@PropertySource、@ComponentScan、@Import、@ImportResource、和@Bean等注解：
protected final SourceClass doProcessConfigurationClass(
ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
throws IOException {
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass, filter);
}
// Process any @PropertySource annotations
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
processPropertySource(propertySource);
}
else {
logger.info("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 immediately
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();
}
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
// Process any @Import annotations
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
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// 递归对配置类父类进行处理
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;
}
对于@PropertySource注解，会根据注解属性找到对应文件，并添加/替换到容器的environment中。ConfigurationClassParser#processPropertySource()：
private void processPropertySource(AnnotationAttributes propertySource) throws IOException {
// 获取文件地址
String name = propertySource.getString("name");
if (!StringUtils.hasLength(name)) {
name = null;
}
String encoding = propertySource.getString("encoding");
if (!StringUtils.hasLength(encoding)) {
encoding = null;
}
String[] locations = propertySource.getStringArray("value");
Assert.isTrue(locations.length > 0, "At least one @PropertySource(value) location is required");
boolean ignoreResourceNotFound = propertySource.getBoolean("ignoreResourceNotFound");
Class<? extends PropertySourceFactory> factoryClass = propertySource.getClass("factory");
PropertySourceFactory factory = (factoryClass == PropertySourceFactory.class ?
DEFAULT_PROPERTY_SOURCE_FACTORY : BeanUtils.instantiateClass(factoryClass));
// 添加/替换文件
for (String location : locations) {
try {
String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);
Resource resource = this.resourceLoader.getResource(resolvedLocation);
addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));
}
catch (IllegalArgumentException | FileNotFoundException | UnknownHostException | SocketException ex) {
// Placeholders not resolvable or resource not found when trying to open it
if (ignoreResourceNotFound) {
if (logger.isInfoEnabled()) {
logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
}
}
else {
throw ex;
}
}
}
}
对于@ComponentScan和@ComponentScan注解，会获取指定的扫描路径，使用ClassPathBeanDefinitionScanner进行扫描。ComponentScanAnnotationParser#parse()：
public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, String declaringClass) {
// 创建&配置ClassPathBeanDefinitionScanner
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);
}
// 获取指定包路径
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);
}
});
// 扫描指定路径
return scanner.doScan(StringUtils.toStringArray(basePackages));
}
对于@Import注解，会通过ImportSelector实现类、ImportBeanDefinitionRegistrar实现类或@Configuration配置类三种方式分别处理。ConfigurationClassParser#processImports()：
private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
Collection<SourceClass> importCandidates, Predicate<String> exclusionFilter,
boolean checkForCircularImports) {
if (importCandidates.isEmpty()) {
return;
}
if (checkForCircularImports && isChainedImportOnStack(configClass)) {
this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
}
else {
this.importStack.push(configClass);
try {
// 遍历@Import注解属性值：根据不同接口策略进行分别注册BeanDefinition
for (SourceClass candidate : importCandidates) {
if (candidate.isAssignable(ImportSelector.class)) {
// ImportSelector实现类 -> delegate to it to determine imports
Class<?> candidateClass = candidate.loadClass();
ImportSelector selector = ParserStrategyUtils.instantiateClass(candidateClass, ImportSelector.class,
this.environment, this.resourceLoader, this.registry);
Predicate<String> selectorFilter = selector.getExclusionFilter();
if (selectorFilter != null) {
exclusionFilter = exclusionFilter.or(selectorFilter);
}
if (selector instanceof DeferredImportSelector) {
this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
}
else {
String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames, exclusionFilter);
processImports(configClass, currentSourceClass, importSourceClasses, exclusionFilter, false);
}
}
else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
//ImportBeanDefinitionRegistrar实现类 -> delegate to it to register additional bean definitions
Class<?> candidateClass = candidate.loadClass();
ImportBeanDefinitionRegistrar registrar =
ParserStrategyUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class,
this.environment, this.resourceLoader, this.registry);
configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
}
else {
// 不是ImportSelector/ImportBeanDefinitionRegistrar实现类 -> 作为@Configuration配置类去处理
this.importStack.registerImport(
currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
processConfigurationClass(candidate.asConfigClass(configClass), exclusionFilter);
}
}
}
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();
}
}
}
对于@ImportResource注解，会获取对应的配置文件地址（.groovy或.xml），通过对应的BeanDefinitionReader实现类注册：
AnnotationAttributes importResource =
AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
// 获取配置文件地址
String[] resources = importResource.getStringArray("locations");
// 获取该配置文件对应的BeanDefinitionReader实现类：XmlBeanDefinitionReader或GroovyBeanDefinitionReader
Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
// 加入配置文件缓存
for (String resource : resources) {
String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
configClass.addImportedResource(resolvedResource, readerClass);
}
}
对于@Bean注解（包括接口中声明的默认方法），会通过ASM按声明顺序获取标注的所有方法，然后添加到配置类的beanMethods缓存中。ConfigurationClassParser#retrieveBeanMethodMetadata()：
private Set<MethodMetadata> retrieveBeanMethodMetadata(SourceClass sourceClass) {
AnnotationMetadata original = sourceClass.getMetadata();
Set<MethodMetadata> beanMethods = original.getAnnotatedMethods(Bean.class.getName());
if (beanMethods.size() > 1 && original instanceof StandardAnnotationMetadata) {
// Try reading the class file via ASM for deterministic declaration order...
// Unfortunately, the JVM's standard reflection returns methods in arbitrary
// order, even between different runs of the same application on the same JVM.
try {
AnnotationMetadata asm =
this.metadataReaderFactory.getMetadataReader(original.getClassName()).getAnnotationMetadata();
Set<MethodMetadata> asmMethods = asm.getAnnotatedMethods(Bean.class.getName());
if (asmMethods.size() >= beanMethods.size()) {
Set<MethodMetadata> selectedMethods = new LinkedHashSet<>(asmMethods.size());
for (MethodMetadata asmMethod : asmMethods) {
for (MethodMetadata beanMethod : beanMethods) {
if (beanMethod.getMethodName().equals(asmMethod.getMethodName())) {
selectedMethods.add(beanMethod);
break;
}
}
}
if (selectedMethods.size() == beanMethods.size()) {
// All reflection-detected methods found in ASM method set -> proceed
beanMethods = selectedMethods;
}
}
}
catch (IOException ex) {
logger.debug("Failed to read class file via ASM for determining @Bean method order", ex);
// No worries, let's continue with the reflection metadata we started with...
}
}
return beanMethods;
}
2.2.2 增强配置类
ConfigurationClassPostProcessor#enhanceConfigurationClasses()方法会对所有配置类进行增强
ConfigurationClassPostProcessor#enhanceConfigurationClasses()：
public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {
StartupStep enhanceConfigClasses = this.applicationStartup.start("spring.context.config-classes.enhance");
Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<>();
// 遍历所有BeanDefinition
for (String beanName : beanFactory.getBeanDefinitionNames()) {
BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);
Object configClassAttr = beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE);
AnnotationMetadata annotationMetadata = null;
MethodMetadata methodMetadata = null;
if (beanDef instanceof AnnotatedBeanDefinition) {
AnnotatedBeanDefinition annotatedBeanDefinition = (AnnotatedBeanDefinition) beanDef;
annotationMetadata = annotatedBeanDefinition.getMetadata();
methodMetadata = annotatedBeanDefinition.getFactoryMethodMetadata();
}
if ((configClassAttr != null || methodMetadata != null) && beanDef instanceof AbstractBeanDefinition) {
// Configuration class (full or lite) or a configuration-derived @Bean method
// -> eagerly resolve bean class at this point, unless it's a 'lite' configuration
// or component class without @Bean methods.
AbstractBeanDefinition abd = (AbstractBeanDefinition) beanDef;
if (!abd.hasBeanClass()) {
boolean liteConfigurationCandidateWithoutBeanMethods =
(ConfigurationClassUtils.CONFIGURATION_CLASS_LITE.equals(configClassAttr) &&
annotationMetadata != null && !ConfigurationClassUtils.hasBeanMethods(annotationMetadata));
if (!liteConfigurationCandidateWithoutBeanMethods) {
try {
abd.resolveBeanClass(this.beanClassLoader);
}
catch (Throwable ex) {
throw new IllegalStateException(
"Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
}
}
}
}
if (ConfigurationClassUtils.CONFIGURATION_CLASS_FULL.equals(configClassAttr)) {
if (!(beanDef instanceof AbstractBeanDefinition)) {
throw new BeanDefinitionStoreException("Cannot enhance @Configuration bean definition '" +
beanName + "' since it is not stored in an AbstractBeanDefinition subclass");
}
else if (logger.isInfoEnabled() && beanFactory.containsSingleton(beanName)) {
logger.info("Cannot enhance @Configuration bean definition '" + beanName +
"' since its singleton instance has been created too early. The typical cause " +
"is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor " +
"return type: Consider declaring such methods as 'static'.");
}
configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);
}
}
if (configBeanDefs.isEmpty() || NativeDetector.inNativeImage()) {
// nothing to enhance -> return immediately
enhanceConfigClasses.end();
return;
}
// 使用CGLIB动态代理增强配置类
ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
AbstractBeanDefinition beanDef = entry.getValue();
// If a @Configuration class gets proxied, always proxy the target class
beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
// Set enhanced subclass of the user-specified bean class
Class<?> configClass = beanDef.getBeanClass();
// 创建代理配置类
Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);
if (configClass != enhancedClass) {
if (logger.isTraceEnabled()) {
logger.trace(String.format("Replacing bean definition '%s' existing class '%s' with " +
"enhanced class '%s'", entry.getKey(), configClass.getName(), enhancedClass.getName()));
}
// 将代理配置类设为beanClass
beanDef.setBeanClass(enhancedClass);
}
}
enhanceConfigClasses.tag("classCount", () -> String.valueOf(configBeanDefs.keySet().size())).end();
}
在创建代理配置类时，会注册BeanMethodInterceptor和BeanFactoryAwareMethodInterceptor回调。
BeanMethodInterceptor会对@Bean方法进行拦截，从容器中获取bean。ConfigurationClassEnhancer.BeanMethodInterceptor#intercept()：
public Object intercept(Object enhancedConfigInstance, Method beanMethod, Object[] beanMethodArgs,
MethodProxy cglibMethodProxy) throws Throwable {
ConfigurableBeanFactory beanFactory = getBeanFactory(enhancedConfigInstance);
// 获取beanName
String beanName = BeanAnnotationHelper.determineBeanNameFor(beanMethod);
// Determine whether this bean is a scoped-proxy
if (BeanAnnotationHelper.isScopedProxy(beanMethod)) {
String scopedBeanName = ScopedProxyCreator.getTargetBeanName(beanName);
if (beanFactory.isCurrentlyInCreation(scopedBeanName)) {
beanName = scopedBeanName;
}
}
// FactoryBean处理流程：
// To handle the case of an inter-bean method reference, we must explicitly check the
// container for already cached instances.
// First, check to see if the requested bean is a FactoryBean. If so, create a subclass
// proxy that intercepts calls to getObject() and returns any cached bean instance.
// This ensures that the semantics of calling a FactoryBean from within @Bean methods
// is the same as that of referring to a FactoryBean within XML. See SPR-6602.
if (factoryContainsBean(beanFactory, BeanFactory.FACTORY_BEAN_PREFIX + beanName) &&
factoryContainsBean(beanFactory, beanName)) {
Object factoryBean = beanFactory.getBean(BeanFactory.FACTORY_BEAN_PREFIX + beanName);
if (factoryBean instanceof ScopedProxyFactoryBean) {
// Scoped proxy factory beans are a special case and should not be further proxied
}
else {
// It is a candidate FactoryBean - go ahead with enhancement
return enhanceFactoryBean(factoryBean, beanMethod.getReturnType(), beanFactory, beanName);
}
}
if (isCurrentlyInvokedFactoryMethod(beanMethod)) {
// The factory is calling the bean method in order to instantiate and register the bean
// (i.e. via a getBean() call) -> invoke the super implementation of the method to actually
// create the bean instance.
if (logger.isInfoEnabled() &&
BeanFactoryPostProcessor.class.isAssignableFrom(beanMethod.getReturnType())) {
logger.info(String.format("@Bean method %s.%s is non-static and returns an object " +
"assignable to Spring's BeanFactoryPostProcessor interface. This will " +
"result in a failure to process annotations such as @Autowired, " +
"@Resource and @PostConstruct within the method's declaring " +
"@Configuration class. Add the 'static' modifier to this method to avoid " +
"these container lifecycle issues; see @Bean javadoc for complete details.",
beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName()));
}
return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs);
}
// 处理bean引用：从容器中获取对应bean
return resolveBeanReference(beanMethod, beanMethodArgs, beanFactory, beanName);
}
BeanFactoryAwareMethodInterceptor则会对BeanFactoryAware#setBeanFactory()方法进行拦截：
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
Field field = ReflectionUtils.findField(obj.getClass(), BEAN_FACTORY_FIELD);
Assert.state(field != null, "Unable to find generated BeanFactory field");
field.set(obj, args[0]);
// Does the actual (non-CGLIB) superclass implement BeanFactoryAware?
// If so, call its setBeanFactory() method. If not, just exit.
if (BeanFactoryAware.class.isAssignableFrom(ClassUtils.getUserClass(obj.getClass().getSuperclass()))) {
return proxy.invokeSuper(obj, args);
}
return null;
}
2.2.3 注册ImportAwareBeanPostProcessor
ConfigurationClassPostProcessor还会注册ImportAwareBeanPostProcessor，它是一个BeanPostProcessor，会在bean实例化过程中进行功能增强。
ConfigurationClassPostProcessor.ImportAwareBeanPostProcessor#postProcessProperties()会为实现EnchancedConfiguration接口的bean设置beanFactory：
public PropertyValues postProcessProperties(@Nullable PropertyValues pvs, Object bean, String beanName) {
// Inject the BeanFactory before AutowiredAnnotationBeanPostProcessor's
// postProcessProperties method attempts to autowire other configuration beans.
if (bean instanceof EnhancedConfiguration) {
((EnhancedConfiguration) bean).setBeanFactory(this.beanFactory);
}
return pvs;
}
ConfigurationClassPostProcessor.ImportAwareBeanPostProcessor#postProcessBeforeInitialization()会为实现ImportAware接口的bean设置@Import引入的注解元信息：
public Object postProcessBeforeInitialization(Object bean, String beanName) {
if (bean instanceof ImportAware) {
ImportRegistry ir = this.beanFactory.getBean(IMPORT_REGISTRY_BEAN_NAME, ImportRegistry.class);
AnnotationMetadata importingClass = ir.getImportingClassFor(ClassUtils.getUserClass(bean).getName());
if (importingClass != null) {
((ImportAware) bean).setImportMetadata(importingClass);
}
}
return bean;
}
