spring-framework 版本：v5.3.19
文章目录
- bean的加载
- bean的创建
- 总结
- getBean流程
- createBean流程
- doCreateBean流程
bean的加载
beanFactory的genBean最常用的一个实现就是AbstractBeanFactory.getBean()。
以ApplicationContext为例，流程是: ApplicationContext.getBean()----》BeanFactory.getBean()----》AbstractBeanFactory.getBean()
而真正做事情的是deGetBean方法
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
//获取beanName
String beanName = transformedBeanName(name);
Object beanInstance;
//无论是什么作用域都先尝试从单例池获取
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isTraceEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
}
}
//有时候并不是放回实例本身，而是返回其映射的实例。如：BeanFactory情况下返回指定方法返回的实例
beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
//当原型模式下有循环依赖时，抛异常（原型模式下若存在循环依赖会导致内存泄漏）
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
//尝试从父beanFactory加载bean
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
//如果不是仅仅做类型检查则是创建bean，这里进行记录
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate")
.tag("beanName", name);
try {
if (requiredType != null) {
beanCreation.tag("beanType", requiredType::toString);
}
//得到合并后的beanDefinition
RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
//检查beanDefinition，抽象的beanDefinition会报错
checkMergedBeanDefinition(mbd, beanName, args);
//先加载dependsOn标注的bean
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
//dePendsOn引起的循环依赖，抛异常
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
//注册dependentBeanMap（dependsOn 于哪些bean）和注册dependenciesForBeanMap（被哪些bean dependOn）
registerDependentBean(dep, beanName);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
//-----------------------------------开始创建bean-----------------------------------------------
//单例模式
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
});
beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
//原型模式
else if (mbd.isPrototype()) {
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
//其他模式
else {
String scopeName = mbd.getScope();
if (!StringUtils.hasLength(scopeName)) {
throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
}
Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new ScopeNotActiveException(beanName, scopeName, ex);
}
}
}
catch (BeansException ex) {
beanCreation.tag("exception", ex.getClass().toString());
beanCreation.tag("message", String.valueOf(ex.getMessage()));
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
finally {
beanCreation.end();
}
}
//必要时进行类型转换
return adaptBeanInstance(name, beanInstance, requiredType);
}
bean的创建
从bean的加载中得知，当一个从缓存中获取不到的时候就会调用createBean方法去创建一个bean。而在AbstractBeanFactory中这是一个抽象方法，具体的创建逻辑由具体的beanFactory类自行实现。至少目前为止，spring内置的实现只有AbstractAutowireCapableBeanFactory.createBean()。无论是AnnotationConfigApplicationContext还是ClassPathXmlApplicationContext创建bean的逻辑最终都会来到这个方法。
虽然AnnotationConfigApplicationContext和ClassPathXmlApplicationContext并不直接继承AbstractAutowireCapableBeanFactory。但是都维护了一个DefaultListableBeanFactory成员变量，而这个成员变量继承自AbstractAutowireCapableBeanFactory。
createBean
doCreateBean
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
//如果是单例，factoryBeanCache.remove
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
//实例化bean
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
//MergedBeanDefinitionPostProcessor的应用（如：AutowiredAnnotationBeanPostProcessor）
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;
}
}
//提前暴露bean，循环依赖处理
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));
}
Object exposedObject = bean;
try {
//属性填充
//填充属性之前会调用 InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation
//填充属性之后会调用 InstantiationAwareBeanPostProcessor.postProcessProperties --如果返回null--> postProcessPropertyValues
populateBean(beanName, mbd, instanceWrapper);
//初始化bean（是指据配置自定义的初始化bean如：@PostConstruct，而不是指构造方法的初始化）
//初始化之前会调用 PostProcessors.postProcessBeforeInitialization
//初始化之后会调用 PostProcessors.postProcessAfterInstantiation
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);
}
}
//循环依赖检查，判断是否需要抛出异常
if (earlySingletonExposure) {
Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!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.");
}
}
}
}
//注册DisposableBean，如果配置了destroy-methoy，这里需要注册以便于在销毁的时候调用
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
initializeBean
总结
getBean流程
1：transformedBeanName(name) 转换为对应的beanName
2：getSingleton(beanName) 尝试从缓存中加载单例
3：isPrototypeCurrentlyIncreation(beanName) 原型模式的依赖检查
4：检测父BeanFactory
5：getMergedLocalBeanDefinition(beanName) GernericBeanDefinition转换为RootBeanDefinition
6：依赖检测
7：根据不同的模式创建bean
8：getObjectForBeanInstance(prototypeInstance, name, beanName, mbd) 根据得到的Bean获取真正对象
9：如果需要则做类型转换
createBean流程
1：锁定class
2：指定方法的覆盖
3：InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation
4：doCreateBean
doCreateBean流程
1：若为单例，移除factoryBeanCache内的缓存
2：实例化Bean
3：MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition（如：AutowiredAnnotationBeanPostProcessor）
4：提前暴露bean，循环依赖处理
(populateBean)
5：InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation
6：属性填充
7：InstantiationAwareBeanPostProcessor.postProcessProperties --如果返回null–> postProcessPropertyValues
(initializeBean)
8：aware方法的执行（beanNameAware，beanClassLoaderAware，beanFactoryAware）
9：PostProcessors.postProcessBeforeInitialization
10：自定义初始化bean（如：InitializingBean.afterPropertiesSet，@PostConstruct，init-method）
11：PostProcessors.postProcessAfterInstantiation
12：循环依赖检查，判断是否需要抛出异常
13：注册DisposableBean
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