@Configuration注解用于标识一个类是配置类,用于声明和组织Bean定义,首先@Configuration本身也是一个@Component,在其注解定义上标有@Component
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {}
通常使用配置类作为参数传递给AnnotationContext,
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(EnvConfig.class);
然后将该类作为一个bean进行初始化,AnnotationConfigApplicationContext在实例化的时候会调用
AnnotationConfigUtils#registerAnnotationConfigProcessors注册必要的bean处理器,这里就会注册一个与解析Configuration相关的类:ConfigurationClassPostProcessor
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));
}
ConfigurationClassPostProcessor 实现了BeanDefinitionRegistryPostProcessor,是一个bean定义后置处理器。在sprnig 的容器refresh方法里有一步操作
invokeBeanFactoryPostProcessors(beanFactory);
这里会拿出所有的BeanDefinitionRegistryPostProcessor进行调用其postProcessBeanDefinitionRegistry(registry)方法。这一步发生在bean实例化之前用于扩展beanDef。
后置处理方法会调用postProcessBeanDefinitionRegistry。然后拿出所有的beanDef寻找@Configuration标识的bean。
判断是否是配置bean方法ConfigurationClassUtils#checkConfigurationClassCandidate
public static boolean checkConfigurationClassCandidate(
BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) {
String className = beanDef.getBeanClassName();
AnnotationMetadata metadata;
if (beanDef instanceof AnnotatedBeanDefinition &&
className.equals(((AnnotatedBeanDefinition) beanDef).getMetadata().getClassName())) {
// Can reuse the pre-parsed metadata from the given BeanDefinition...
metadata = ((AnnotatedBeanDefinition) beanDef).getMetadata();
}
else if (beanDef instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) beanDef).hasBeanClass()) {
// Check already loaded Class if present...
//这几个类型的跳过
Class<?> beanClass = ((AbstractBeanDefinition) beanDef).getBeanClass();
if (BeanFactoryPostProcessor.class.isAssignableFrom(beanClass) ||
BeanPostProcessor.class.isAssignableFrom(beanClass) ||
AopInfrastructureBean.class.isAssignableFrom(beanClass) ||
EventListenerFactory.class.isAssignableFrom(beanClass)) {
return false;
}
metadata = AnnotationMetadata.introspect(beanClass);
}
else {//获取metadata
MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(className);
metadata = metadataReader.getAnnotationMetadata();
}
//解读Configuration注解配置,config能解到证明是一个配置bean
Map<String, Object> config = metadata.getAnnotationAttributes(Configuration.class.getName());
if (config != null && !Boolean.FALSE.equals(config.get("proxyBeanMethods"))) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
}
else if (config != null || isConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
}
else {
return false;
}
// It's a full or lite configuration candidate... Let's determine the order value, if any.
Integer order = getOrder(metadata);
if (order != null) {
beanDef.setAttribute(ORDER_ATTRIBUTE, order);
}
return true;
}
然后解析的到的配置bean会经过ConfigurationClassParser类进行配置解析,具体解析方法在processConfigurationClass,真正解析方法doProcessConfigurationClass
1、PropertySource解析
//获取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);//解析配置文件
}
else {
logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
"]. Reason: Environment must implement ConfigurableEnvironment");
}
}
可以在配置bean类上通过@PropertySource注解进行properties配置文件的加载。
@PropertySource("classpath:a.properties")
也可以通过@PropertySources加载多个文件.
2、ComponentScan解析
ComponentScan可以定义扫描bean的包路径,这里spring容器会根据ComponentScan配置的包路径取寻找@Component标注的bean。
@ComponentScan(basePackages = {"com.test.service"})
解析源码
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
//会调用scanner.doScan方法进行bean定义的发现
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());
}
}
}
}
3、解析@Import
//getImports方法获取@Import注解引入的类
processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
这里判断import的bean是否是ImportSelector、ImportBeanDefinitionRegistrar进行不同的处理,如果都不是安默认按照是一个配置bean进行解析。
4、解析@ImportResource
这个注解主要是引入xml配置进行解析
5、解析方法bean
配置bean里可以通过方法上@Bean注解进行bean的定义
@Bean
public EnvService envService(){
EnvService service = new EnvService();
return service;
}
通过retrieveBeanMethodMetadata方法获取方法上有@Bean注解的进行解析。
上面解析的几个步骤解析结果会包装成一个ConfigurationClass,然后通过ConfigurationClassBeanDefinitionReader#loadBeanDefinitionsFromImportedResources方法将beandef加载到beanFacotry中。这里ComponentScan注解不会走这里,在scan过程中已完成。