Bean-生命周期
目录
生命周期
既然大家都放这个图，那我也放吧：
主要流程
Bean 的生命周期概括起来就是 4 个阶段：
- 实例化（Instantiation）
- 属性赋值（Populate）
- 初始化（Initialization）
- 销毁（Destruction）
看什么都没有直接看源代码清楚，来吧，上代码：
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>5.3.7</version>
</dependency>
AbstractAutowireCapableBeanFactory.java
doCreateBean()
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {
//1-实例化
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = (BeanWrapper)this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = this.createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
synchronized(mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
this.applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
} catch (Throwable var17) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", var17);
}
mbd.postProcessed = true;
}
}
boolean earlySingletonExposure = mbd.isSingleton() && this.allowCircularReferences && this.isSingletonCurrentlyInCreation(beanName);
if (earlySingletonExposure) {
if (this.logger.isTraceEnabled()) {
this.logger.trace("Eagerly caching bean '" + beanName + "' to allow for resolving potential circular references");
}
this.addSingletonFactory(beanName, () -> {
return this.getEarlyBeanReference(beanName, mbd, bean);
});
}
Object exposedObject = bean;
try {
//2-属性赋值
this.populateBean(beanName, mbd, instanceWrapper);
//3-初始化
exposedObject = this.initializeBean(beanName, exposedObject, mbd);
} catch (Throwable var18) {
if (var18 instanceof BeanCreationException && beanName.equals(((BeanCreationException)var18).getBeanName())) {
throw (BeanCreationException)var18;
}
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", var18);
}
if (earlySingletonExposure) {
Object earlySingletonReference = this.getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
} else if (!this.allowRawInjectionDespiteWrapping && this.hasDependentBean(beanName)) {
String[] dependentBeans = this.getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet(dependentBeans.length);
String[] var12 = dependentBeans;
int var13 = dependentBeans.length;
for(int var14 = 0; var14 < var13; ++var14) {
String dependentBean = var12[var14];
if (!this.removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName, "Bean with name '" + beanName + "' has been injected into other beans [" + StringUtils.collectionToCommaDelimitedString(actualDependentBeans) + "] in its raw version as part of a circular reference, but has eventually been wrapped. This means that said other beans do not use the final version of the bean. This is often the result of over-eager type matching - consider using 'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
//4-销毁-注册回调接口
try {
this.registerDisposableBeanIfNecessary(beanName, bean, mbd);
return exposedObject;
} catch (BeanDefinitionValidationException var16) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", var16);
}
}
由于初始化包含了第 3~7步，较复杂，所以我们进到 initializeBean() 方法里具体看下其过程（注释的序号对应图中序号）：
initializeBean()
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
//3-检查 Aware 相关接口并设置相关依赖
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(() -> {
//Aware系列接口，主要用于辅助Spring bean访问Spring容器
this.invokeAwareMethods(beanName, bean);
return null;
}, this.getAccessControlContext());
} else {
this.invokeAwareMethods(beanName, bean);
}
// 4-BeanPostProcessor 前置处理
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = this.applyBeanPostProcessorsBeforeInitialization(bean, beanName);
}
// 5-若实现 InitializingBean 接口，调用 afterPropertiesSet() 方法,这俩个方法都在invokeInitMethods里面
// 6-若配置自定义的 init-method方法，则执行
try {
this.invokeInitMethods(beanName, wrappedBean, mbd);
} catch (Throwable var6) {
throw new BeanCreationException(mbd != null ? mbd.getResourceDescription() : null, beanName, "Invocation of init method failed", var6);
}
// 7-BeanPostProceesor 后置处理
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = this.applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
DisposableBeanAdapter.java
销毁的过程
public void destroy() {
if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {
Iterator var1 = this.beanPostProcessors.iterator();
while(var1.hasNext()) {
DestructionAwareBeanPostProcessor processor = (DestructionAwareBeanPostProcessor)var1.next();
processor.postProcessBeforeDestruction(this.bean, this.beanName);
}
}
//// 9-若实现 DisposableBean 接口，则执行 destory()方法
if (this.invokeDisposableBean) {
if (logger.isTraceEnabled()) {
logger.trace("Invoking destroy() on bean with name '" + this.beanName + "'");
}
try {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(() -> {
((DisposableBean)this.bean).destroy();
return null;
}, this.acc);
} else {
((DisposableBean)this.bean).destroy();
}
} catch (Throwable var3) {
String msg = "Invocation of destroy method failed on bean with name '" + this.beanName + "'";
if (logger.isDebugEnabled()) {
logger.warn(msg, var3);
} else {
logger.warn(msg + ": " + var3);
}
}
}
// 10-若配置自定义的 detory-method 方法，则执行
if (this.destroyMethod != null) {
this.invokeCustomDestroyMethod(this.destroyMethod);
} else if (this.destroyMethodName != null) {
Method methodToInvoke = this.determineDestroyMethod(this.destroyMethodName);
if (methodToInvoke != null) {
this.invokeCustomDestroyMethod(ClassUtils.getInterfaceMethodIfPossible(methodToInvoke));
}
}
}
注解方式
在 bean 初始化时会经历几个阶段，首先可以使用注解 @PostConstruct, @PreDestroy 来在 bean 的创建和销毁阶段进行调用:
@Component
public class AnnotationBean {
private final static Logger LOGGER = LoggerFactory.getLogger(AnnotationBean.class);
@PostConstruct
public void start(){
LOGGER.info("AnnotationBean start");
}
@PreDestroy
public void destroy(){
LOGGER.info("AnnotationBean destroy");
}
}
InitializingBean, DisposableBean 接口
还可以实现 InitializingBean,DisposableBean 这两个接口，也是在初始化以及销毁阶段调用：
@Service
public class SpringLifeCycleService implements InitializingBean,DisposableBean{
private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleService.class);
@Override
public void afterPropertiesSet() throws Exception {
LOGGER.info("SpringLifeCycleService start");
}
@Override
public void destroy() throws Exception {
LOGGER.info("SpringLifeCycleService destroy");
}
}
自定义初始化和销毁方法
也可以自定义方法用于在初始化、销毁阶段调用:
@Configuration
public class LifeCycleConfig {
@Bean(initMethod = "start", destroyMethod = "destroy")
public SpringLifeCycle create(){
SpringLifeCycle springLifeCycle = new SpringLifeCycle() ;
return springLifeCycle ;
}
}
public class SpringLifeCycle{
private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycle.class);
public void start(){
LOGGER.info("SpringLifeCycle start");
}
public void destroy(){
LOGGER.info("SpringLifeCycle destroy");
}
}
以上是在 SpringBoot 中可以这样配置，如果是原始的基于 XML 也是可以使用:
<bean class="com.crossoverjie.spring.SpringLifeCycle" init-method="start" destroy-method="destroy">
</bean>
扩展点的作用
Aware 接口
若 Spring 检测到 bean 实现了 Aware 接口，则会为其注入相应的依赖。所以通过让bean 实现 Aware 接口，则能在 bean 中获得相应的 Spring 容器资源。
Spring 中提供的 Aware 接口有：
- BeanNameAware：注入当前 bean 对应 beanName；
- BeanClassLoaderAware：注入加载当前 bean 的 ClassLoader；
- BeanFactoryAware：注入 当前BeanFactory容器 的引用。
其代码实现如下：
// AbstractAutowireCapableBeanFactory.java
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 = this.getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware)bean).setBeanClassLoader(bcl);
}
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware)bean).setBeanFactory(this);
}
}
}
以上是针对 BeanFactory 类型的容器，而对于 ApplicationContext 类型的容器，也提供了 Aware 接口，只不过这些 Aware 接口的注入实现，是通过 BeanPostProcessor 的方式注入的，但其作用仍是注入依赖。
- EnvironmentAware：注入 Enviroment，一般用于获取配置属性；
- EmbeddedValueResolverAware：注入 EmbeddedValueResolver（Spring EL解析器），一般用于参数解析；
- ApplicationContextAware（ResourceLoader、ApplicationEventPublisherAware、MessageSourceAware）：注入 ApplicationContext 容器本身。
其代码实现如下：
// ApplicationContextAwareProcessor.java
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);
}
}
实现 Aware 接口
例子：
@Component
public class SpringLifeCycleAware implements ApplicationContextAware {
private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleAware.class);
private ApplicationContext applicationContext ;
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext ;
LOGGER.info("SpringLifeCycleAware start");
}
}
BeanPostProcessor
实现 BeanPostProcessor 接口，Spring 中所有 bean 在做初始化时都会调用该接口中的两个方法，可以用于对一些特殊的 bean 进行处理：
public interface BeanPostProcessor {
// 初始化前置处理
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
// 初始化后置处理
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
}
常用场景有：
- 对于标记接口的实现类，进行自定义处理。例如3.1节中所说的ApplicationContextAwareProcessor，为其注入相应依赖；再举个例子，自定义对实现解密接口的类，将对其属性进行解密处理；
- 为当前对象提供代理实现。
例如 Spring AOP 功能，生成对象的代理类，然后返回。
// AbstractAutoProxyCreator.java
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) {
TargetSource targetSource = getCustomTargetSource(beanClass, beanName);
if (targetSource != null) {
if (StringUtils.hasLength(beanName)) {
this.targetSourcedBeans.add(beanName);
}
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(beanClass, beanName, targetSource);
Object proxy = createProxy(beanClass, beanName, specificInterceptors, targetSource);
this.proxyTypes.put(cacheKey, proxy.getClass());
// 返回代理类
return proxy;
}
return null;
}
例子：
@Component
public class SpringLifeCycleProcessor implements BeanPostProcessor {
private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleProcessor.class);
/**
* 预初始化 初始化之前调用
* @param bean
* @param beanName
* @return
* @throws BeansException
*/
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if ("annotationBean".equals(beanName)){
LOGGER.info("SpringLifeCycleProcessor start beanName={}",beanName);
}
return bean;
}
/**
* 后初始化 bean 初始化完成调用
* @param bean
* @param beanName
* @return
* @throws BeansException
*/
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if ("annotationBean".equals(beanName)){
LOGGER.info("SpringLifeCycleProcessor end beanName={}",beanName);
}
return bean;
}
}
//结果
结果： 00:40:24.856 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor start beanName=annotationBean
结果： 00:40:24.860 [restartedMain] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean start
结果： 00:40:24.861 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor end beanName=annotationBean
结果： 00:40:24.864 [restartedMain] INFO c.c.s.aware.SpringLifeCycleAware - SpringLifeCycleAware start
结果： 00:40:24.867 [restartedMain] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService start
结果： 00:40:24.887 [restartedMain] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle start
结果： 00:40:25.062 [restartedMain] INFO o.s.b.d.a.OptionalLiveReloadServer - LiveReload server is running on port 35729
结果： 00:40:25.122 [restartedMain] INFO o.s.j.e.a.AnnotationMBeanExporter - Registering beans for JMX exposure on startup
结果： 00:40:25.140 [restartedMain] INFO com.crossoverjie.Application - Started Application in 2.309 seconds (JVM running for 3.681)
结果： 00:40:25.143 [restartedMain] INFO com.crossoverjie.Application - start ok!
结果： 00:40:25.153 [Thread-8] INFO o.s.c.a.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@3913adad: startup date [Wed Mar 21 00:40:23 CST 2018]; root of context hierarchy
结果： 00:40:25.155 [Thread-8] INFO o.s.j.e.a.AnnotationMBeanExporter - Unregistering JMX-exposed beans on shutdown
结果： 00:40:25.156 [Thread-8] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle destroy
结果： 00:40:25.156 [Thread-8] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService destroy
结果： 00:40:25.156 [Thread-8] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean destroy
直到 Spring 上下文销毁时则会调用自定义的销毁方法以及实现了 DisposableBean 的 destroy() 方法。
InitializingBean 和 init-method
InitializingBean 和 init-method 是 Spring 为 bean 初始化提供的扩展点。
InitializingBean接口 的定义如下：
public interface InitializingBean {
void afterPropertiesSet() throws Exception;
}
在 afterPropertiesSet() 方法写初始化逻辑。
指定 init-method 方法，指定初始化方法：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="demo" class="com.chaycao.Demo" init-method="init()"/>
</beans>
DisposableBean 和 destory-method 与上述类似，就不描述了。
总结
最后总结下如何记忆 Spring Bean 的生命周期：
- 首先是实例化、属性赋值、初始化、销毁这 4 个大阶段；
- 再是初始化的具体操作，有 Aware 接口的依赖注入、BeanPostProcessor 在初始化前后的处理以及 InitializingBean 和 init-method 的初始化操作；
- 销毁的具体操作，有注册相关销毁回调接口，最后通过DisposableBean 和 destory-method 进行销毁。
作用域
详情请见：
