1、BeanFactory.getBean(String name)方法
//AbstractBeanFactory.java
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
2、真正创建Bean的地方--doCreateBean()
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
//提取对应的beanName,比如去掉FactoryBean的前缀“&”
final String beanName = transformedBeanName(name);
Object bean;
/*
在创建单例bean的时候会存在依赖注入的情况,为了避免循环依赖
Spring在创建bean的时候,是不能bean创建完成就会将创建bean的ObjectFactory提早曝光
*/
// 尝试从缓存中获取或者singletonFactories中的objectFactort获取
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
//返回bean的实例。如果不是FactoryBean则直接返回,否则会调用getObject返回bean,并且将bean放入factoryBean对应的缓存中
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// 检测是否有循环依赖
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// 如果当前的beanFactory不包含该bean,就从parentBeanFactory中查找、创建
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
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 {
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
// --------------------------------------------------------------------
//如果不仅仅是做类型检测,而是需要创建bean,则需要记录该bean被创建
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
//将xml配置文件的GernericBeanDefinition转换为RootBeanDefinition。如果需要创建的bean有父bean的话,还会合并父bean的属性
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
//验证isAbstract属性,如果bean定义为abstract则会抛出异常
checkMergedBeanDefinition(mbd, beanName, args);
// 如果存在依赖,则递归实例化依赖的bean
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {