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這篇文章給大家介紹Spring Bean有哪些生命周期，內(nèi)容非常詳細，感興趣的小伙伴們可以參考借鑒，希望對大家能有所幫助。
生命周期解讀：
1. 注冊階段 2. 實例化階段 3. 初始化階段 4. 銷毀階段
注冊階段主要任務是通過各種BeanDefinitionReader讀取掃描各種配置來源信息（xml文件、注解等），并轉換為BeanDefinition的過程。
BeanDefinition可以理解為類的定義，描述一個類的基本情況，比較像我們注冊某些網(wǎng)站時的基本信息，比如需要填寫姓名、住址、出生日期等。
最終會將我們掃描到的類整體注冊到一個DefaultListableBeanFactory的Map容器中，便于我們之后獲取使用。
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
//存儲注冊信息的BeanDefinition
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
//beanDefinitionMap的數(shù)據(jù)結構是ConcurrentHashMap，因此不能保證順序，為了記錄注冊的順序，這里使用了ArrayList類型beanDefinitionNames用來記錄注冊順序
private volatile List<String> beanDefinitionNames = new ArrayList<>(256);
//省略部分代碼.......
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException {
//省略判斷代碼.......
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
}
}在實例化階段，Spring主要將BeanDefinition轉換為實例Bean，并放在包裝類BeanWrapper中。
無論是否設置Bean的懶加載方式，最后都會通過AbstractBeanFactory.getBean()方法進行實例化，并進入到AbstractAutowireCapableBeanFactory.createBean()方法。
public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory implements AutowireCapableBeanFactory {
//省略部分代碼......
@Nullable
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
//實例化前處理器
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
//實例化后處理器
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}
//省略部分代碼......
}在實例化階段AbstractAutowireCapableBeanFactory.createBeanInstance()完成Bean的創(chuàng)建，并放到BeanWrapper中。
初始化階段主要是在返回Bean之前做一些處理，主要由AbstractAutowireCapableBeanFactory.initializeBean()方法實現(xiàn)。
public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory implements AutowireCapableBeanFactory {
//省略部分代碼......
//真正創(chuàng)建Bean的方法
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
//省略部分代碼......
// Initialize the bean instance.
//Bean對象的初始化，依賴注入在此觸發(fā)
//這個exposedObject在初始化完成之后返回作為依賴注入完成后的Bean
Object exposedObject = bean;
try {
//將Bean實例對象封裝，并且Bean定義中配置的屬性值賦值給實例對象
populateBean(beanName, mbd, instanceWrapper);
//初始化Bean對象
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {
if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
//省略部分代碼......
return exposedObject;
}
//初始容器創(chuàng)建的Bean實例對象，為其添加BeanPostProcessor后置處理器
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
//JDK的安全機制驗證權限
if (System.getSecurityManager() != null) {
//實現(xiàn)PrivilegedAction接口的匿名內(nèi)部類
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
//為Bean實例對象包裝相關屬性，如名稱，類加載器，所屬容器等信息
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
//對BeanPostProcessor后置處理器的postProcessBeforeInitialization
//回調(diào)方法的調(diào)用，為Bean實例初始化前做一些處理
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
//調(diào)用Bean實例對象初始化的方法，這個初始化方法是在Spring Bean定義配置
//文件中通過init-method屬性指定的
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
//對BeanPostProcessor后置處理器的postProcessAfterInitialization
//回調(diào)方法的調(diào)用，為Bean實例初始化之后做一些處理
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
//省略部分代碼......
}一般是在ApplicationContext關閉的時候調(diào)用，也就是AbstractApplicationContext.close() 方法。
在注冊的時候Spring通過適配器模式包裝了一個類DisposableBeanAdapter，在銷毀階段的時候會獲得這個類，進而調(diào)用到DisposableBeanAdapter.destroy()方法：
class DisposableBeanAdapter implements DisposableBean, Runnable, Serializable {
//省略部分代碼......
@Override
public void destroy() {
if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {
for (DestructionAwareBeanPostProcessor processor : this.beanPostProcessors) {
processor.postProcessBeforeDestruction(this.bean, this.beanName);
}
}
if (this.invokeDisposableBean) {
if (logger.isDebugEnabled()) {
logger.debug("Invoking destroy() on bean with name '" + this.beanName + "'");
}
try {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
((DisposableBean) bean).destroy();
return null;
}, acc);
}
else {
((DisposableBean) bean).destroy();
}
}
catch (Throwable ex) {
String msg = "Invocation of destroy method failed on bean with name '" + this.beanName + "'";
if (logger.isDebugEnabled()) {
logger.warn(msg, ex);
}
else {
logger.warn(msg + ": " + ex);
}
}
}
if (this.destroyMethod != null) {
invokeCustomDestroyMethod(this.destroyMethod);
}
else if (this.destroyMethodName != null) {
Method methodToCall = determineDestroyMethod(this.destroyMethodName);
if (methodToCall != null) {
invokeCustomDestroyMethod(methodToCall);
}
}
}
//省略部分代碼......
}銷毀階段主要包括三個銷毀途徑，按照執(zhí)行順序：
@PreDestroy注解，主要通過DestructionAwareBeanPostProcessor實現(xiàn)
實現(xiàn)DisposableBean接口，主要通過DisposableBean.destroy()實現(xiàn)
自定義銷毀方 DisposableBeanAdapter.invokeCustomDestroyMethod()實現(xiàn)
下邊通過一個簡單實例來做一個簡單測試。
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
/**
* @Author: maomao
* @Date: 2021-04-18 20:50
*/
public class User implements BeanFactoryAware, BeanNameAware, InitializingBean, DisposableBean, ApplicationContextAware, ApplicationEventPublisherAware {
private String name;
private int age;
private BeanFactory beanFactory;
private String beanName;
public User(){
System.out.println("User【構造方法】默認構造方法！");
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
System.out.println("User【注入屬性】name " + name);
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
System.out.println("User【注入屬性】age " + age);
}
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
System.out.println("【BeanFactoryAware接口】調(diào)用setBeanFactory " + beanFactory);
this.beanFactory = beanFactory;
}
@Override
public void setBeanName(String name) {
System.out.println("【BeanNameAware接口】setBeanName " + name);
this.beanName = name;
}
@Override
public void destroy() throws Exception {
System.out.println("【DisposableBean接口】destroy");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("【InitializingBean接口】InitializingBean");
}
public void initMethod(){
System.out.println("【initMethod方法】initMethod");
}
public void destroyMethod(){
System.out.println("【destroyMethod方法】destroyMethod");
}
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
System.out.println("【ApplicationContextAware接口】setApplicationContext " + applicationContext);
}
@Override
public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
System.out.println("【ApplicationEventPublisherAware接口】setApplicationEventPublisher " + applicationEventPublisher);
}
}application.xml配置
<?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="beanPostProcessor" class="com.freecloud.spring.lifecycle.MyBeanPostProcessor"></bean> <bean id="instantiationAwareBeanPostProcessor" class="com.freecloud.spring.lifecycle.MyInstantiationAwareBeanPostProcessor"></bean> <bean id="beanFactoryPostProcessor" class="com.freecloud.spring.lifecycle.MyBeanFactoryPostProcessor"></bean> <bean id="user" class="com.freecloud.spring.lifecycle.User" init-method="initMethod" destroy-method="destroyMethod" > <property name="name" value="張三"></property> <property name="age" value="18"></property> </bean> </beans>
測試類：
import org.junit.Before;
import org.junit.Test;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
/**
* @Author: maomao
* @Date: 2021-04-18 20:57
*/
public class LifecycleTest {
private ConfigurableApplicationContext applicationContext;
@Before
public void init(){
applicationContext = new ClassPathXmlApplicationContext("application.xml");
}
@Test
public void Test(){
User user = applicationContext.getBean("user",User.class);
//ConfigurableApplicationContext.close()將關閉該應用程序的上下文，釋放所有資源，并銷毀所有緩存的單例bean
// 只用于destroy演示
applicationContext.close();
//applicationContext.registerShutdownHook();
System.out.println("\n\n 輸出：" + user.getAge());
}
}最終結果：
關于Spring Bean有哪些生命周期就分享到這里了，希望以上內(nèi)容可以對大家有一定的幫助，可以學到更多知識。如果覺得文章不錯，可以把它分享出去讓更多的人看到。
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