IoC容器加载过程和Bean的生命周期源码深度剖析
目录
1、this(); //获取组件
（1）DefaultListableBeanFactory
（2）BeanDefinitionReader
（3）BeanDefinitionScanner->扫描器，包扫描
2、register(componentClasses)—>注册BeanDefinition
3、refresh() 方法
（1）finishBeanFactoryInitialization—>生产Bean
（2）BeanFactory 和 FactoryBean的区别
Spring IoC加载过程图示，所有的源码跟进依据此图为大纲
从 ApplicationContext 开始，简单的Bean创建、获取和使用流程如下
public class MainStat {
public static void main(String[] args) {
//加载配置文件,生产Bean
ApplicationContext context = new AnnotationConfigApplicationContext(Person.class);
//获取Bean
Person person = (Person) context.getBean("person");
//使用Bean
System.out.println(person.getName());
}
}首先，我们会去获取一个上下文 new AnnotationConfigApplicationContext()；在AnnotationConfigApplicationContext() 中做了三件事情，如下
public AnnotationConfigApplicationContext(Class... componentClasses) {
// 1-生成三大组件：BeanFactory、BeanDefinitionReader、BeanDefinitionScanner
this();
// 2-注册BeanDefinition——>registerBeanDefinition
register(componentClasses);
// 3-Spring重点->Bean生命周期的实现
refresh();
}1、this(); //获取组件
调用 this() 方法，首先会加载父类 GenericApplicationContext.calss 的构造方法，如下
public GenericApplicationContext() {
//1-获取Bean工厂
this.beanFactory = new DefaultListableBeanFactory();
}然后调用 AnnotationConfigApplicationContext.class 自生的构造方法
public AnnotationConfigApplicationContext() {
// 2-BeanDefinitionReader 读取器
this.reader = new AnnotatedBeanDefinitionReader(this);
// 3-BeanDefinitionScanner 扫描器
this.scanner = new ClassPathBeanDefinitionScanner(this);
}（1）DefaultListableBeanFactory //容器
为什么首先要获取DefaultListableBeanFactory？因为 BeanFactory 是 Spring Bean容器(IOC容器)的顶层核心接口，DefaultListableBeanFactory 实现了 BeanFactory 和 Bean定义注册器，它的依赖和继承关系图如下
（2）BeanDefinitionReader // Bean定义
从代码：this.reader = new AnnotatedBeanDefinitionReader(this);
一直往下跟进，直到找到 AnnotationConfigUtils#registerAnnotationConfigProcessors 方法。
在该方法中，我们能看到注册了一些处理器的Bean定义，比如ConfigurationClassPostProcessor，AutowiredAnnotationBeanPostProcessor 等等 // 目的是准备一些后续需要用到的类
//注册一些配置的后置处理器
public static Set registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
//注册了实现Order接口的排序器
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
//设置@AutoWired的候选的解析器
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
}
Set beanDefs = new LinkedHashSet<>(8);
/**
* 为我们容器中注册了解析我们配置类的后置处理器ConfigurationClassPostProcessor
* 名字叫:org.springframework.context.annotation.internalConfigurationAnnotationProcessor
*/
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
/**
* 为我们容器中注册了处理@Autowired 注解的处理器AutowiredAnnotationBeanPostProcessor
* 名字叫:org.springframework.context.annotation.internalAutowiredAnnotationProcessor
*/
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));
}
/**
* 为我们容器中注册处理@Required属性的注解处理器RequiredAnnotationBeanPostProcessor
* 名字叫:org.springframework.context.annotation.internalRequiredAnnotationProcessor
*/
if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
/**
* 为我们容器注册处理JSR规范的注解处理器CommonAnnotationBeanPostProcessor
* org.springframework.context.annotation.internalCommonAnnotationProcessor
*/
if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
}
/**
* 处理jpa注解的处理器org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor
*/
if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition();
try {
def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
AnnotationConfigUtils.class.getClassLoader()));
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
}
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
}
/**
* 处理监听方法的注解解析器EventListenerMethodProcessor
*/
if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}
/**
* 注册事件监听器工厂
*/
if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}
return beanDefs;
} #扩展点
我们以其中一个Processor来做示例，比如ConfigurationClassPostProcessor(会解析加了@Configuration的配置类等)，它实现了BeanFactory的扩展点->BeanFactoryPostProcessor //对照流程图来看
注：PostProcessor是在 refresh() 中 invokeBeanFactoryPostProcessors(beanFactory) 中调用
（3）BeanDefinitionScanner->扫描器，包扫描
ClassPathBeanDefinitionScanner 主要根据路径来进行包扫描，scan() 方法中的 doScan()；
public int scan(String... basePackages) {
int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
//包扫描
doScan(basePackages);
// Register annotation config processors, if necessary.
if (this.includeAnnotationConfig) {
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
}2、register(componentClasses)—>注册BeanDefinition
通过reader，封装BeanDefinition信息 //不断往后边跟，直到找到关键代码
public void register(Class... annotatedClasses) {
Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
//使用reader进行注册
this.reader.register(annotatedClasses);
}封装BeanDefinition信息，设置BeanDefinition的相关属性
最终通过DefaultListableBeanFactory 把 BeanDefinition put 到 beanDefinitionMap 中
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
if (beanDefinition instanceof AbstractBeanDefinition) {
//省略代码...
}
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
//省略大段代码...
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
removeManualSingletonName(beanName);
}
}
else {
// Still in startup registration phase
// 同时往beanDefinitionMap 、beanDefinitionNames(生产Bean时用到) 中存值
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
//省略大段代码...
} 3、refresh() 方法
refresh() 方法中的关键代码
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//1-准备刷新上下文环境
prepareRefresh();
//2-告诉子类刷新内部bean工厂
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//3-对bean工厂进行填充属性
prepareBeanFactory(beanFactory);
try {
//4-允许在上下文子类中对bean工厂进行后处理
postProcessBeanFactory(beanFactory);
//5-调用在上下文中注册为bean的工厂处理器
invokeBeanFactoryPostProcessors(beanFactory);
//6-注册拦截bean创建的bean处理器
registerBeanPostProcessors(beanFactory);
//7-为此上下文初始化消息源-国际化
initMessageSource();
//8-为此上下文初始化事件多播
initApplicationEventMulticaster();
//9-初始化特定上下文子类中的其他特殊bean
onRefresh();
//10-检查侦听器bean并注册它们
registerListeners();
//11-实例化所有剩余的（非惰性初始化）单例。
finishBeanFactoryInitialization(beanFactory);
//12-最后一步：发布相应的事件。
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
//销毁已经创建的单例以避免悬空的资源。
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
// 重置Spring核心中常见的内省缓存，因为我们可能不再需要单例bean的元数据了。
resetCommonCaches();
}
}
}Spring refresh() 方法中有很多方法，在此我们只关注IOC的加载流程和步骤，其他部分后续再详细拆分。
（1）finishBeanFactoryInitialization—>生产Bean
跟进去，找到创建Bean的代码，这段代码在 AbstractBeanFactory 中
protected T doGetBean(final String name, @Nullable final Class requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
// 省略大段代码 ...
// Create bean instance. 创建Bean实例
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
//创建Bean
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
// 省略大段代码 ...
} 具体实现代码如下，其中 doCreateBean(beanName, mbdToUse, args); 进行真正的Bean创建
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
//省略大段代码...
try {
//实例创建前，第一次调用Bean的后置处理器-InstantiationAwareBeanPostProcessor
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
//如果后置处理器InstantiationAwareBeanPostProcessor(实现此接口)创建了Bean
//将直接返回，不再执行后续的创建步骤
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
//该步骤真正的创建Bean——>Bean的生命周期(实例化，属性赋值初始化)
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isTraceEnabled()) {
logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
//省略代码...
}我们来详细看看这个方法里边的实现，代码如下，其中我们可以详细的看到Bean创建的生命周期（实例化—>属性赋值—>初始化）
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//1-实例化
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//获取到实例化对象，暂未赋值
final Object bean = instanceWrapper.getWrappedInstance();
Class beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
//允许后处理器修改合并的bean定义。
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
//解决循环依赖相关
//缓存单例，以便能够解析循环引用,即使是由BeanFactoryAware等生命周期接口触发。
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//2-属性赋值
populateBean(beanName, mbd, instanceWrapper);
//3-初始化 ->一堆Aware的调用(更多的通过后置处理器调用)
//调用初始化回调方法：（1）@PostConstruct（2）InitializingBean接口 （3）init-method
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {
//省略代码...
}
//省略大段代码...
return exposedObject;
}在Bean的初始化方法中（initializeBean(beanName, exposedObject, mbd)），我们可以看到Spring对一堆Aware方法的调用和一些初始化回调方法的调用
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction最终Spring会把生成的Bean放入到一级缓存，Spring IOC的加载过程，也就到此结束了。
（2）BeanFactory 和 FactoryBean的区别
BeanFactory
BeanFactory定义了IOC容器的最基本形式，并提供了IOC容器应遵守的的最基本的接口，也就是Spring IOC所遵守的最底层和最基本的编程规范。在Spring代码中，BeanFactory只是个接口，并不是IOC容器的具体实现，但是Spring容器给出了很多种实现，如 DefaultListableBeanFactory、XmlBeanFactory、ApplicationContext等，都是附加了某种功能的实现。
FactoryBean
一般情况下，Spring通过反射机制利用
public class Person implements FactoryBean {
private String name;
private String sex;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
//实现了FactoryBean，最终获取到的实例是WoMen("Jerry",18) 而非 Person
@Override
public WoMen getObject() throws Exception {
return new WoMen("Jerry",18);
}
//获取到的是WoMen类
@Override
public Class getObjectType() {
return WoMen.class;
}
}直接强转会报错，因为此时拿到的对象是WoMen
修改下类型接收类型，如下
如果需要强制获取Person的原装Bean，可以在BeanName前加 '&'
区别
BeanFactory是个Factory，也就是IOC容器或对象工厂，FactoryBean是个特殊的Bean。在Spring中，所有的Bean都是由BeanFactory(也就是IOC容器)来进行管理的，没有BeanFactory就没有Bean的存在。对于FactoryBean接口，被它修饰的Bean，将成为一个特殊的Bean，原本的Bean将被隐藏，而是由FactoryBean的getObject()返回最终的Bean。