spring Bean的初始化过程解析

AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors

使用BeanPostProcessor收集带有注解的方法和属性，方便下面初始化时调用。
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors

protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof MergedBeanDefinitionPostProcessor) {
MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
}
}
}

这里的BeanPostProcessor主要有以下两个：

• AutowiredAnnotationBeanPostProcessor：负责@Autowired、@Value

• CommonAnnotationBeanPostProcessor：负责@Resource、@PostConstruct、@PreDestroy

AutowiredAnnotationBeanPostProcessor#buildAutowiringMetadata

AutowiredAnnotationBeanPostProcessor负责@Autowired、@Value注解的方法和属性的收集。

org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#buildAutowiringMetadata

private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) {
// autowiredAnnotationTypes是在构造方法中被初始化的
// autowiredAnnotationTypes @Autowired @Value
if (!AnnotationUtils.isCandidateClass(clazz, this.autowiredAnnotationTypes)) {
return InjectionMetadata.EMPTY;
}
List<InjectionMetadata.InjectedElement> elements = new ArrayList<>();
Class<?> targetClass = clazz;
do {
final List<InjectionMetadata.InjectedElement> currElements = new ArrayList<>();
// 查找带有@Autowired注解的属性
ReflectionUtils.doWithLocalFields(targetClass, field -> {
MergedAnnotation<?> 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));
}
});
// 查找带有@Autowired注解的方法
ReflectionUtils.doWithLocalMethods(targetClass, method -> {
Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) {
return;
}
MergedAnnotation<?> ann = findAutowiredAnnotation(bridgedMethod);
if (ann != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) {
if (Modifier.isStatic(method.getModifiers())) {
if (logger.isInfoEnabled()) {
logger.info("Autowired annotation is not supported on static methods: " + method);
}
return;
}
if (method.getParameterCount() == 0) {
if (logger.isInfoEnabled()) {
logger.info("Autowired annotation should only be used on methods with parameters: " +
method);
}
}
boolean required = determineRequiredStatus(ann);
PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz);
currElements.add(new AutowiredMethodElement(method, required, pd));
}
});
elements.addAll(0, currElements);
targetClass = targetClass.getSuperclass();
}
while (targetClass != null && targetClass != Object.class);
return InjectionMetadata.forElements(elements, clazz);
}

CommonAnnotationBeanPostProcessor#postProcessMergedBeanDefinition

CommonAnnotationBeanPostProcessor负责@Resource、@PostConstruct、@PreDestroy注解的方法和属性的收集，收集过程与AutowiredAnnotationBeanPostProcessor的收集过程类似。

org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#postProcessMergedBeanDefinition

public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
// 构造方法会注入@PostConstruct、@PreDestroy
// 父类会查找带有@PostConstruct、@PreDestroy注解的方法
super.postProcessMergedBeanDefinition(beanDefinition, beanType, beanName);
// 查找带有@Resource注解的属性和方法
InjectionMetadata metadata = findResourceMetadata(beanName, beanType, null);
metadata.checkConfigMembers(beanDefinition);
}

AbstractAutowireCapableBeanFactory#populateBean

调用各个BeanPostProcessor.postProcessProperties对属性进行设置。

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
... ...
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
// 调用各个BeanPostProcessor.postProcessProperties对属性进行设置
/**
* AutowiredAnnotationBeanPostProcessor处理@Autowired
* CommonAnnotationBeanPostProcessor处理@Resource
*
* @see AutowiredAnnotationBeanPostProcessor#postProcessProperties(org.springframework.beans.PropertyValues, java.lang.Object, java.lang.String)
* @see org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#postProcessProperties(org.springframework.beans.PropertyValues, java.lang.Object, java.lang.String)
*/
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);

... ...
}

CommonAnnotationBeanPostProcessor#postProcessProperties

对带有@Resource注解的属性进行设置，对带有@Resource注解的方法进行调用。

org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#postProcessProperties

public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
// 上面的方法postProcessMergedBeanDefinition向缓存中设置了@PostConstruct、@PreDestroy注解的方法，@Resource注解的属性和方法
// 这里会从缓存中取出对这些属性进行设置，方法进行调用
InjectionMetadata metadata = findResourceMetadata(beanName, bean.getClass(), pvs);
try {
/**
* @see org.springframework.beans.factory.annotation.InjectionMetadata#inject(java.lang.Object, java.lang.String, org.springframework.beans.PropertyValues)
*/
metadata.inject(bean, beanName, pvs);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Injection of resource dependencies failed", ex);
}
return pvs;
}

AutowiredAnnotationBeanPostProcessor#postProcessProperties方法也是如此，对带有@Autowired注解的属性进行设置，对带有@Autowired注解的方法进行调用。

InjectionMetadata#inject

org.springframework.beans.factory.annotation.InjectionMetadata#inject

public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
Collection<InjectedElement> checkedElements = this.checkedElements;
Collection<InjectedElement> elementsToIterate =
(checkedElements != null ? checkedElements : this.injectedElements);
if (!elementsToIterate.isEmpty()) {
for (InjectedElement element : elementsToIterate) {
/**
* CommonAnnotationBeanPostProcessor注入的是InjectionMetadata.InjectedElement对象
* @see InjectedElement#inject(java.lang.Object, java.lang.String, org.springframework.beans.PropertyValues)
*
* AutowiredAnnotationBeanPostProcessor注入的是AutowiredFieldElement和AutowiredMethodElement
* @see AutowiredAnnotationBeanPostProcessor.AutowiredFieldElement#inject(java.lang.Object, java.lang.String, org.springframework.beans.PropertyValues)
* @see AutowiredAnnotationBeanPostProcessor.AutowiredMethodElement#inject(java.lang.Object, java.lang.String, org.springframework.beans.PropertyValues)
*/
element.inject(target, beanName, pvs);
}
}
}

InjectedElement的调用主要是反射进行属性的设置和方法的调用，如果属性是引用类型，将会触发beanFactory.getBean()方法从Spring容器中获取对象。

AbstractAutowireCapableBeanFactory#initializeBean

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)

上面的populateBean()完成了对象的初始化，下面将会调用对象的初始化方法完成最后的初始化过程。

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
// 调用aware方法
// BeanNameAware/BeanClassLoaderAware/BeanFactoryAware对应的setXxx方法
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 处理EnvironmentAware/EmbeddedValueResolverAware/ResourceLoaderAware/
// ApplicationEventPublisherAware/MessageSourceAware/ApplicationContextAware
// 处理@PostConstruct
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// InitializingBean.afterPropertiesSet()
// 调用init-method
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
// AOP代理入口
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}

AbstractAutowireCapableBeanFactory#invokeAwareMethods

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeAwareMethods

这里只完成了BeanNameAware、BeanClassLoaderAware、BeanFactoryAware接口的初始化方法调用，还有部分aware接口将通过下面的BeanPostProcessor完成调用。

private void invokeAwareMethods(String beanName, Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}

AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsBeforeInitialization

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsBeforeInitialization

public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
/**
* ApplicationContextAwareProcessor调用EnvironmentAware/EmbeddedValueResolverAware/ResourceLoaderAware/
* ApplicationEventPublisherAware/MessageSourceAware/ApplicationContextAware
*
* ImportAwareBeanPostProcessor调用ImportAware（Bean不仅需要实现ImportAware接口，还要有@Import注解）
* InitDestroyAnnotationBeanPostProcessor 处理@PostConstruct
*
* @see org.springframework.context.support.ApplicationContextAwareProcessor#postProcessBeforeInitialization(java.lang.Object, java.lang.String)
* @see org.springframework.context.annotation.ConfigurationClassPostProcessor.ImportAwareBeanPostProcessor#postProcessBeforeInitialization(java.lang.Object, java.lang.String)
* @see org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor#postProcessBeforeInitialization(java.lang.Object, java.lang.String)
*/
Object current = processor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}

ApplicationContextAwareProcessor#postProcessBeforeInitialization

ApplicationContextAwareProcessor负责EnvironmentAware、EmbeddedValueResolverAware、ResourceLoaderAware、ApplicationEventPublisherAware、MessageSourceAware、ApplicationContextAware接口的调用。

org.springframework.context.support.ApplicationContextAwareProcessor#postProcessBeforeInitialization

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
return bean;
}
AccessControlContext acc = null;
if (System.getSecurityManager() != null) {
acc = this.applicationContext.getBeanFactory().getAccessControlContext();
}
if (acc != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareInterfaces(bean);
return null;
}, acc);
}
else {
invokeAwareInterfaces(bean);
}
return bean;
}
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof EnvironmentAware) {
((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
}
if (bean instanceof EmbeddedValueResolverAware) {
((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
}
if (bean instanceof ResourceLoaderAware) {
((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
}
if (bean instanceof ApplicationEventPublisherAware) {
((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
}
if (bean instanceof MessageSourceAware) {
((MessageSourceAware) bean).setMessageSource(this.applicationContext);
}
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}

ImportAwareBeanPostProcessor#postProcessBeforeInitialization

ImportAwareBeanPostProcessor主要负责ImportAware接口的调用。

ImportAware的具体使用如下：

ImportAwareBean.java

package com.morris.spring.entity.imports;

import org.springframework.context.annotation.ImportAware;
import org.springframework.core.type.AnnotationMetadata;

public class ImportAwareBean implements ImportAware {
@Override
public void setImportMetadata(AnnotationMetadata importMetadata) {
// 在这里可以拿到注入ImportAwareBean的类ImportConfig上的注解@Transactional
System.out.println(importMetadata.getAnnotationTypes());
}
}

ImportConfig.java

package com.morris.spring.config;

import com.morris.spring.entity.imports.ImportAwareBean;
import org.springframework.context.annotation.Import;
import org.springframework.transaction.annotation.Transactional;
@Transactional
@Import(ImportAwareBean.class)
public class ImportConfig {
}

org.springframework.context.annotation.ConfigurationClassPostProcessor.ImportAwareBeanPostProcessor#postProcessBeforeInitialization

public Object postProcessBeforeInitialization(Object bean, String beanName) {
if (bean instanceof ImportAware) {
ImportRegistry ir = this.beanFactory.getBean(IMPORT_REGISTRY_BEAN_NAME, ImportRegistry.class);
// bean必须通过@Import注解注入进来，importingClass才会有值
AnnotationMetadata importingClass = ir.getImportingClassFor(ClassUtils.getUserClass(bean).getName());
if (importingClass != null) {
((ImportAware) bean).setImportMetadata(importingClass);
}
}
return bean;
}

InitDestroyAnnotationBeanPostProcessor#postProcessBeforeInitialization

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
// LifecycleMetadata缓存数据从何来？
// 前面在调用CommonAnnotationBeanPostProcessor#postProcessMergedBeanDefinition收集@Resource注解时，同时会调用
// 父类InitDestroyAnnotationBeanPostProcessor#postProcessMergedBeanDefinition收集@PostConstruct注解

// 负责@PostConstruct方法的调用
LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
try {
metadata.invokeInitMethods(bean, beanName);
}
catch (InvocationTargetException ex) {
throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException());
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Failed to invoke init method", ex);
}
return bean;
}

LifecycleMetadata缓存数据从何来？前面在调用CommonAnnotationBeanPostProcessor#postProcessMergedBeanDefinition收集@Resource注解时，同时会调用
父类InitDestroyAnnotationBeanPostProcessor#postProcessMergedBeanDefinition收集@PostConstruct注解。

而PostConstruct注解是在CommonAnnotationBeanPostProcessor的构造方法中指定的。

public CommonAnnotationBeanPostProcessor() {
setOrder(Ordered.LOWEST_PRECEDENCE - 3);
setInitAnnotationType(PostConstruct.class);
setDestroyAnnotationType(PreDestroy.class);
ignoreResourceType("javax.xml.ws.WebServiceContext");
}

AbstractAutowireCapableBeanFactory#invokeInitMethods

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeInitMethods

protected void invokeInitMethods(String beanName, Object bean, @Nullable RootBeanDefinition mbd)
throws Throwable {
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isTraceEnabled()) {
logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
((InitializingBean) bean).afterPropertiesSet();
return null;
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
// 调用InitializingBean.afterPropertiesSet()
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null && bean.getClass() != NullBean.class) {
String initMethodName = mbd.getInitMethodName();
if (StringUtils.hasLength(initMethodName) &&
!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
// 调用init-method
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}

@PostConstruct、afterPropertiesSet、init-method

@PostConstruct、InitializingBean.afterPropertiesSet、init-method这三者要实现的功能都是一致的，都是在bean实例化并初始化完成之后进行调用。

具体使用如下：

InitBean.java

package com.morris.spring.entity;

import org.springframework.beans.factory.InitializingBean;
import javax.annotation.PostConstruct;
public class InitBean implements InitializingBean {
@PostConstruct
public void postConstruct() {
System.out.println("PostConstruct");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("afterPropertiesSet");
public void init(){
System.out.println("init");
}

InitDemo.java

package com.morris.spring.demo.annotation;

import com.morris.spring.entity.InitBean;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class InitDemo {
@Bean(initMethod = "init")
public InitBean initBean() {
return new InitBean();
}
public static void main(String[] args) {
new AnnotationConfigApplicationContext(InitDemo.class);
}

运行结果如下：

PostConstruct
afterPropertiesSet
init

运行结果与源码分析的一致，先执行PostConstruct，再执行afterPropertiesSet，最后initMethod。

注意这三种初始化方法都不能带有参数。

来源：https://blog.csdn.net/u022812849/article/details/123394691