先说最关键的两个类，之前的Spring Boot系列也多次提到过BeanFactoryPostProcessor（allows for custom modification of an application context's bean definitions，A BeanFactoryPostProcessor may interact with and modify bean definitions, but never bean instances）和BeanPostProcessor（Factory hook that allows for custom modification of new bean instances,e.g. checking for marker interfaces or wrapping them with proxies）。
在上文提到的AnnotationConfigServletWebServerApplicationContext（即Spring Boot默认的ApplicationContext）里面有个AnnotatedBeanDefinitionReader属性，
AnnotatedBeanDefinitionReader会向BeanFactory注册各种BeanFactoryPostProcessor和BeanPostProcessor，其中的ConfigurationClassPostProcessor主要负责ConfigurationClass的解析（used for bootstrapping processing of{@link Configuration @Configuration} classes），此处为Bean加载的入口，在后续的处理过程中会陆续加入各种BeanFactoryProcessor和BeanPostProcessor用于扩展（如有需要，我们均可以自定义），如下：
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));
}
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass);
// Process any @PropertySource annotations
...
// 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), true);
// Process any @ImportResource annotations
...
// 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);
// Process superclass, if any
...
private void initializePropertySources() {
...
CompositePropertySource composite = new CompositePropertySource(PropertySourcesConstants.APOLLO_PROPERTY_SOURCE_NAME);
//sort by order asc
ImmutableSortedSet<Integer> orders = ImmutableSortedSet.copyOf(NAMESPACE_NAMES.keySet());
Iterator<Integer> iterator = orders.iterator();
while (iterator.hasNext()) {
int order = iterator.next();
for (String namespace : NAMESPACE_NAMES.get(order)) {
Config config = ConfigService.getConfig(namespace);
composite.addPropertySource(configPropertySourceFactory.getConfigPropertySource(namespace, config));
}
}
// add after the bootstrap property source or to the first
if (environment.getPropertySources()
.contains(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
environment.getPropertySources()
.addAfter(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME, composite);
} else {
environment.getPropertySources().addFirst(composite);
}
}
@Override
public void onChange(ConfigChangeEvent changeEvent) {
...
for (String key : keys) {
// 1. check whether the changed key is relevant
Collection<SpringValue> targetValues = `springValueRegistry`.get(key);
if (targetValues == null || targetValues.isEmpty()) {
continue;
}
// 2. check whether the value is really changed or not (since spring property sources have hierarchies)
if (!shouldTriggerAutoUpdate(changeEvent, key)) {
continue;
}
// 3. update the value
for (SpringValue val : targetValues) {
updateSpringValue(val);
}
}
}
