1 Bean 初始化阶段划分
- Bean 初始化前阶段
- Bean 初始化阶段
- Bean 初始化后阶段
- Bean 初始化完成阶段
2 Bean 初始化各阶段详细分析
2.1 Bean 初始化前阶段
BeanPostProcessor#postProcessBeforeInitialization
2.1.1 代码示例
...
class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {
...
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (ObjectUtils.nullSafeEquals("userHolder", beanName) && UserHolder.class.equals(bean.getClass())) {
UserHolder userHolder = (UserHolder) bean;
userHolder.setDescription("the user holder v3");
}
return bean;
}
...
}
2.1.2 源码讲解
方法入口：AbstractAutowireCapableBeanFactory#initializeBean
...
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
...
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
...
}
...
@Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
...
2.2 初始化阶段
- @PostConstruct 标注方法
- 实现 InitializingBean 接口的 afterPropertiesSet() 方法
- 自定义初始化方法
2.2.1 代码示例
<?xml version="1.0" encoding="UTF-8"?>
<beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/beans/spring-context.xsd">
<bean class="org.wmg.thinking.in.spring.bean.lifecycle.MyInstantiationAwareBeanPostProcessor" />
<bean id = "userHolder" class="org.wmg.thinking.in.spring.bean.lifecycle.UserHolder" autowire="constructor" init-method="init">
<!-- 通过 XML 元素配置 -->
<property name="description" value="the user holder" />
</bean>
</beans>
...
public class UserHolder implements InitializingBean {
...
@PostConstruct
public void initPostConstruct() {
// postProcessBeforeInitialization v3 -> initPostConstruct v4
this.description = "the user holder v4";
System.out.println("initPostConstruct() = " + description);
}
@Override
public void afterPropertiesSet() throws Exception {
// initPostConstruct v4 -> afterPropertiesSet v5
this.description = "the user holder v5";
System.out.println("afterPropertiesSet() = " + description);
}
/**
* 自定义初始化方法
*/
public void init() {
// afterPropertiesSet v5 -> init v6
this.description = "the user holder v6";
System.out.println("init() = " + description);
}
...
}
2.2.2 源码讲解
...
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
...
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
...
}
...
protected void invokeInitMethods(String beanName, final 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 {
((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)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
...
2.3 初始化后阶段
BeanPostProcessor#postProcessAfterInitialization
2.3.1 代码示例
...
class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {
...
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (ObjectUtils.nullSafeEquals("userHolder", beanName) && UserHolder.class.equals(bean.getClass()))
return bean;
}
}
2.3.2 源码讲解
...
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
...
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
...
}
...
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
...
2.4 初始化完成阶段
SmartInitializingSingleton#afterSingletonsInstantiated
2.4.1 代码示例
...
public class UserHolder implements SmartInitializingSingleton {
...
@Override
public void afterSingletonsInstantiated() {
// postProcessAfterInitialization v7 -> init v8
this.description = "the user holder v8";
System.out.println("afterSingletonsInstantiated() = " + description);
}
}
...
public class BeanInitializationLifecycleDemo {
public static void main(String[] args) {
executeBeanFactory();
}
private static void executeBeanFactory() {
DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
// 方法一： 添加 BeanPostProcessor 实现（示例）
beanFactory.addBeanPostProcessor(new MyInstantiationAwareBeanPostProcessor());
// 添加 CommonAnnotationBeanPostProcessor 解决 @PostConstructor
beanFactory.addBeanPostProcessor(new CommonAnnotationBeanPostProcessor());
// 方法二：将 MyInstantiationAwareBeanPostProcessor 作为 Bean 注册
// 基于 XML 资源 BeanDefinitionReader 实现
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
String[] locations = {"META-INF/dependency-lookup-context.xml",
"META-INF/bean-constructor-dependency-injection.xml"};
int beanNumbers = beanDefinitionReader.loadBeanDefinitions(locations);
System.out.println("已加载 BeanDefinition 数量：" + beanNumbers);
// 显示执行 preInstantiateSingletons()
// SmartInitliziingSingleton 通常在 Spring ApplicationContext 场景使用。
// preInstantiateSingletons() 将已注册的 BeanDefinition 初始化成 Spring Bean
beanFactory.preInstantiateSingletons();
// 通过 Bean id 和类型进行依赖查找
User user = beanFactory.getBean("user", User.class);
System.out.println(user);
User superUser = beanFactory.getBean("superUser", User.class);
System.out.println(superUser);
// 构造器注入按照类型注入，resolveDependency
UserHolder userHolder = beanFactory.getBean("userHolder", UserHolder.class);
System.out.println(userHolder);
}
}
2.4.2 源码讲解
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
...
@Override
public void preInstantiateSingletons() throws BeansException {
...
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
...
}
