1 ConfigurationClassPostProcessor 介绍
实现
@Configutarion
注解配置的核心类。该类实现了BeanFactoryPostProcessor
后置处理接口,该接口是Spring提供的一个扩展钩子类,通过回调来对BeanDefinition进行修改,从而干预bean的创建。
2 注册ConfigurationClassPostProcessor
组件
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));
}
该类是Spring容器的内部组件,容器在启动时,会调用registerAnnotationConfigProcessors
方法主动注册一个该对象的bean实例。注意:xml扫描方式的容器和annotation注解类型的容器注册的时机稍微不同。
3 解析过程分析
3.1 入口
refresh
容器启动方法中会调用invokeBeanFactoryPostProcessors
回调容器中注册的内部后处理器。然后委托给PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors
静态方法处理。
伪代码:
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// 省略了前面的无关逻辑
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// 根据类型获取容器中注册的BeanDefinitionRegistryPostProcessor
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
// 进行筛选,这里分了两步。这里对PriorityOrdered、Ordered类型的分别进行处理。
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
// 排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
// 回调筛选后的BeanDefinitionRegistryPostProcessor
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// 同上
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);
}
3.2 ConfigurationClassParser
上面的方法最后会回调ConfigurationClassPostProcessor
类的postProcessBeanDefinitionRegistry
方法。该方法类首先提取候选的待处理配置类,然后创建一个ConfigurationClassParser
解析器,借助该解析器进行处理。
processConfigBeanDefinitions
方法部分代码:
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();
// 获取解析配置类得到的bean对象类型。
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());
}
// 注册beanDefinition
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);
candidates.clear();
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;
}
}
while (!candidates.isEmpty());
创建一个ConfigurationClassParser
解析器,然后在一个while循环中,调用parse方法解析。直到所有配置类都已经解析过了——即没有新的配置类,退出循环。
3.3 解析
具体解析逻辑在doProcessConfigurationClass
方法中:
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);
}
//处理@PropertySource注解
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");
}
}
// 处理@ComponentScan注解
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());
}
}
}
}
// 处理@Import注解
processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
// 处理@ImportResource注解
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);
}
}
// 处理@Bean注解的方法,即定义的bean
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// 处理实现接口的default方法
processInterfaces(configClass, sourceClass);
// 处理父类,如果有父类,则返回父类,外层while循环会递归处理
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();
}
}
// 没有父类返回null,外层循环结束。
return null;
}
核心方法:定义了处理流程,主要步骤是分别处理了以下几个类型的注解:
- @Component:组件定义
- @PropertySources:处理properties资源文件
- @ComponentScans:组件扫描
- @Import:处理导入配置类或配置扫描类
- @ImportResource:处理导入的配置文件
- @Bean:处理bean实例定义,相当于xml配置文件的<Bean>标签
其中@Bean是作用在方法上的。
这里最复杂的是@Import,因为@Import可以导入其它Configuration配置类,这里着重分析下@Import处理。
@Import介绍
value值是一个Class<?>数组,从注释中我们可以发现,value的class类型可以有三种:
- 被@Configuration注解的Class类:直接导入一个Configuration配置类
- ImportSelecor类型:通过回调改类的selectImports方法,得到一组configuration配置类。
- ImportBeanDefinitionRegistrar类型:回调registerBeanDefinitions方法直接注册beanDefinition
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
/**
* {@link Configuration @Configuration}, {@link ImportSelector},
* {@link ImportBeanDefinitionRegistrar}, or regular component classes to import.
*/
Class<?>[] value();
}
再回头看处理@Import
的processImports
方法
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 {
// 当前处理的类入栈
this.importStack.push(configClass);
try {
// 遍历import的value属性
for (SourceClass candidate : importCandidates) {
// 当前是ImportSelector, 调用selectImports,得到一组配置类,递归处理
if (candidate.isAssignable(ImportSelector.class)) {
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)) {
// 如果是ImportBeanDefinitionRegistrar类型,直接回调注册方法注册beanDefinition
Class<?> candidateClass = candidate.loadClass();
ImportBeanDefinitionRegistrar registrar =
ParserStrategyUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class,
this.environment, this.resourceLoader, this.registry);
configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
}
else {
// 第三种情况,处理Configuration配置类,第一中importselector最终也会转换成处理Configuration配置类。区别就是一个是直接处理一个配置类,一个通过回调方法扫描出一组配置类
this.importStack.registerImport(
currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
// 这里processConfigurationClass方法就是一开始我们处理Configuration的入口,可以发现这里也是一个递归。
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();
}
}
}
总结下来,就是利用递归解析出一个个configuration配置类进行处理。
3.4 注册Bean
配置类最终目的都是配置bean,递归解析完configuration对象后,所有的配置类会被保存在一个set集合中,遍历该集合,调用loadBeanDefinitionsForConfigurationClass
方法,为@Bean注解的方法,解析为BeanDefinition,注册到容器中。
处理逻辑在loadBeanDefinitionsForBeanMethod
方法中。大致步骤就是创建一个ConfigurationClassBeanDefinition类型的BeanDefinition对象,设置FactoryMethodName
参数,即@Bean所作用的方法名。后面实例话bean的时候通过该方法名获取Method
反射对象,通过反射生成Bean实例。
ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass, metadata);
beanDef.setResource(configClass.getResource());
beanDef.setSource(this.sourceExtractor.extractSource(metadata, configClass.getResource()));
if (metadata.isStatic()) {
if (configClass.getMetadata() instanceof StandardAnnotationMetadata) {
beanDef.setBeanClass(((StandardAnnotationMetadata) configClass.getMetadata()).getIntrospectedClass());
}
else {
beanDef.setBeanClassName(configClass.getMetadata().getClassName());
}
beanDef.setUniqueFactoryMethodName(methodName);
}
else {
beanDef.setFactoryBeanName(configClass.getBeanName());
beanDef.setUniqueFactoryMethodName(methodName);
}
4.总结一下@Configuration注解解析过程
- 注册
ConfigurationClassPostProcessor
Spring内部组件。 - 容器启动时,回调
ConfigurationClassPostProcessor
的postProcessBeanDefinitionRegistry
进行后置处理 - 从一个入口配置类开始解析,并递归处理所有@Configuration注解作用的类。主要就是扫描@Bean注解作用的方法,然后解析为一个
ConfigurationClassBeanDefinition
类型的BeanDefinition对象,注册到容器中。
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