SpringBoot中@Autowired生效方式详解
前言
@Component
public class SimpleBean3 {
@Autowired
private SimpleBean simpleBean;
}
@Autowired修饰的字段会被容器自动注入.那么Spring Boot中使如何实现这一功能呢? AutowiredAnnotationBeanPostProcessor!
BeanPostProcessor implementation that autowires annotated fields, setter methods, and arbitrary config methods. Such members to be injected are detected through annotations: by default, spring's @Autowired and @Value annotations.
Also supports jsR-330's @Inject annotation, if available, as a direct alternative to Spring's own @Autowired.
AutowiredAnnotationBeanPostProcessor(以下简称AutowiredProcessor)间接实现了InstantiationAwareBeanPostProcessor接口.通过postProcessProperties(...)完成@Autowired的注入,本文将按照下图流程梳理AutowiredProcessor的生效逻辑.
SpringBoot-autowired.png
正文
注册AutowiredProcessor的BeanDefinition
SpringApplication#createApplicationContext默认会创建 AnnotationConfigApplicationContext,而AnnotationConfigApplicationContext又会创建AnnotatedBeanDefinitionReader
public AnnotationConfigApplicationContext() {
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
AnnotatedBeanDefinitionReader构造时会调用AnnotationConfigUtils.reGISterAnnotationConfigProcessors(this.registry),将AutowiredProcessor的BeanDefinition注册到容器
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
//忽略部分代码...
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
//忽略部分代码...
return beanDefs;
}实例化AutowiredProcessor
在AbstractApplicationContext的refresh阶段,会注册并实例化所有的BeanPostProcessor
public void refresh() throws BeansException, IllegalStateException {
//...忽略部分代码
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// ########### 这里注册所有的BeanPostProcessor ##########
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh()
//...忽略部分代码
}
实际的注册逻辑交给了PostProcessorRegistrationDelegate
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}
在PostProcessorRegistrationDelegate中,获取到所有的BeanPostProcessor(基于BeanDefinition),并将其分为几种类型,并按照不同的优先级进行处理化,这块不是这篇文章的重点,我们只需要知道在这里AutowiredProcessor被注册就可以了.
创建bean时进行注入
以SimpleBean3的注入为例, 它是单例的,在AbstractApplicationContext.refresh()的finishBeanFactoryInitialization(beanFactory)时创建.
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
//...忽略部分代码
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}
调用到了BeanFactory.preInstantiateSingletons(),走到getBean()逻辑
public void preInstantiateSingletons() throws BeansException {
//...忽略部分代码
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
final FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
getBean(beanName);
}
}
}
//...忽略部分代码
}经过一连串的辗转,最终调用到AbstractAutowireCapableBeanFactory#populateBean
附上调用链路
image.png
在populateBean中,会将所有的BeanPostProcessor应用在这个bean上,包括AutowiredProcessor
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
//...忽略部分代码
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
//###### 调用到postProcessProperties #####
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
//...忽略部分代码
}
AutowiredProcessor的postProcessProperties()会进行注入操作,这需要找到注入的元数据(InjectionMetadata)
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
//### 找到AutowringMetadata #####
InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
try {
// #### 注入 ###
metadata.inject(bean, beanName, pvs);
}
catch (BeanCreationException ex) {
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
}
return pvs;
}
findAutowiringMetadata()又调用到buildAutowiringMetadata(),生成代表可注入元素的InjectMetadata
private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) {
List<InjectionMetadata.InjectedElement> elements = new ArrayList<>();
Class<?> targetClass = clazz;
do {
final List<InjectionMetadata.InjectedElement> currElements = new ArrayList<>();
ReflectionUtils.doWithLocalFields(targetClass, field -> {
//###### 找到带有可注入注解的字段
AnnotationAttributes ann = findAutowiredAnnotation(field);
if (ann != null) {
if (Modifier.isStatic(field.getModifiers())) {
if (logger.isInfoEnabled()) {
logger.info("Autowired annotation is not supported on static fields: " + field);
}
return;
}
boolean required = determineRequiredStatus(ann);
currElements.add(new AutowiredFieldElement(field, required));
}
});
//...忽略部分代码
}findAutowiredAnnotation()根据AutowiredProcessor的实例字段autowiredAnnotationTypes,去查看是否匹配,这个字段是在AutowiredProcessor创建时初始化,可以看到支持@Autowired,@Value,@Inject三种类型的注入标识.最终据此完成注入
public AutowiredAnnotationBeanPostProcessor() {
this.autowiredAnnotationTypes.add(Autowired.class);
this.autowiredAnnotationTypes.add(Value.class);
try {
this.autowiredAnnotationTypes.add((Class<? extends Annotation>)
ClassUtils.forName("javax.inject.Inject", AutowiredAnnotationBeanPostProcessor.class.getClassLoader()));
logger.trace("JSR-330 'javax.inject.Inject' annotation found and supported for autowiring");
}
catch (ClassNotFoundException ex) {
// JSR-330 api not available - simply skip.
}
}
后记
最后再来梳理一下整个流程.
首先是AutowiredPorcessor的BeanDefinition的注册
=> 创建ApplicationContext
=> 创建AnnotatedBeanDefinitionReader
=> 注册BeanDefinition registerAnnotationConfigProcessors
然后是AutowiredProcessor注册为bean
=> registerBeanPostProcessors
最后是注入
=> 获取bean getBean()
=> 创建bean doCreateBean()
=>生成bean populateBean()
=> 应用AutowiredProcessor ibp.postProcessProperties()
=> 找到可注入的字段 buildAutowiringMetadata
=> 注入 metadata.inject
至此,@Autowired生效逻辑梳理完成
到此这篇关于SpringBoot中@Autowired生效方式详解的文章就介绍到这了,更多相关SpringBoot @Autowired内容请搜索以前的文章或继续浏览下面的相关文章希望大家以后多多支持！
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