Spring Bean 创建过程
首先调用getBean(“beanName”)；
applicationContext.getBean("name");
然后再调用
org.springframework.context.support.AbstractApplicationContext#getBean(java.lang.String)
@Override public Object getBean(String name) throws BeansException { assertBeanFactoryActive();
// 调用getBean 进入AbstractBeanFactory return getBeanFactory().getBean(name); }
在调用doGetBean
org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
@SuppressWarnings("unchecked")
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
// 做别名解析 删除工厂引用前缀 String FACTORY_BEAN_PREFIX = "&";
final String beanName = transformedBeanName(name);
Object bean;
// 去单例缓存池中去取 如果取到了直接返回
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
// 创建的对象有可能不是我们想要的 也有可能是工厂Bean 在这里做处理 转换为Bean实例进行返回
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// 从单例缓存池中 没有获取到 走这里
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
// 判断是否是原型对象 是原型对象直接抛异常 spring 的原型对象不能解决循环依赖
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
// 判断父容器是否为空 并判断当前beanDefinitionMap 中是否有改bean定义
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) {
// Delegation to parent with explicit args.
// 递归查询
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
// 是否获取实例用于类型检查而不是实际使用(创建Bean做标记)
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
// 合并父子 BeanDefinaitionMap
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
// 判断mdb 四否是抽象的 是的话抛异常
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
// 获取创建依赖对象 进行判断 并处理 如果A 依赖 B 的话 那么检测到后会先创建B
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
// 注册依赖
registerDependentBean(dep, beanName);
try {
// 优先创建依赖对象
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// 创建单实例Bean
// Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
// 创建其它Bean
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
final 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);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
getSingleton 方法解析
org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, boolean)
@Nullable protected Object getSingleton(String beanName, boolean allowEarlyReference) {
// 从缓存池中获取bean singletonObjects 一级缓存 Object singletonObject = this.singletonObjects.get(beanName);
// 如果一级缓存中为null 再判断是否正在创建 if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
// 防止并发创建 synchronized (this.singletonObjects) {
// 早期对象缓存中是否有该对象 singletonObject = this.earlySingletonObjects.get(beanName);
// 早期对象没有 暴露早期对象 放入earlySingletonObjects 用于解决循环依赖
if (singletonObject == null && allowEarlyReference) {
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName); if (singletonFactory != null) {
// 获取早期对象 singletonObject = singletonFactory.getObject();
// 存入早期对象 this.earlySingletonObjects.put(beanName, singletonObject);
// 删除单例缓存工厂中bean this.singletonFactories.remove(beanName); } } } } return singletonObject; }
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