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目录
代码块1:resolveBeforeInstantiation
代码块2:applyBeanPostProcessorsBeforeInstantiation
代码块4.5:determineConstructorsFromBeanPostProcessors
代码块6:resolveConstructorArguments
代码块16:determineAutowireCandidate
代码块17:determinePrimaryCandidate
代码块18:determineHighestPriorityCandidate
Spring IoC源码学习全系列
Spring IoC源码学习:ApplicationContext 刷新前的配置
Spring IoC源码学习:obtainFreshBeanFactory详解
Spring IoC源码学习:parseDefaultElement详解
Spring IoC源码学习:parseCustomElement详解
Spring IoC源码学习:context:component-scan 节点详解
Spring IoC源码学习:invokeBeanFactoryPostProcessors详解
Spring IoC源码学习:registerBeanPostProcessors详解
Spring IoC源码学习:finishBeanFactoryInitialization详解
Spring IoC源码学习:createBean详解(上)
Spring IoC源码学习:createBean详解(下)
Spring IoC源码学习:finishRefresh 详解
前言
接着 Spring IoC:getBean详解,我们继续解析获取 bean 实例里的核心内容:创建 bean 实例。
正文
首先,我们进入 createBean 方法。
createBean
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
if (logger.isDebugEnabled()) {
logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
// 1.解析beanName对应的Bean的类型,例如:com.joonwhee.open.demo.service.impl.UserServiceImpl
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
// 如果resolvedClass存在,并且mdb的beanClass类型不是Class,并且mdb的beanClass不为空(则代表beanClass存的是Class的name),
// 则使用mdb深拷贝一个新的RootBeanDefinition副本,并且将解析的Class赋值给拷贝的RootBeanDefinition副本的beanClass属性,
// 该拷贝副本取代mdb用于后续的操作
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
try {
// 2.验证及准备覆盖的方法(对override属性进行标记及验证)
mbdToUse.prepareMethodOverrides();
} catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
// 3.实例化前的处理,给InstantiationAwareBeanPostProcessor一个机会返回代理对象来替代真正的bean实例,达到“短路”效果
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
// 4.如果bean不为空,则会跳过Spring默认的实例化过程,直接使用返回的bean
if (bean != null) {
return bean;
}
} catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
// 5.创建Bean实例(真正创建Bean的方法)
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
// 6.返回创建的Bean实例
return beanInstance;
}
3.实例化前的处理,给 InstantiationAwareBeanPostProcessor 一个机会返回代理对象来替代真正的 bean 实例,从而跳过 Spring 默认的实例化过程,达到“短路”效果,见代码块1详解。
5.创建 bean 实例,见代码块3详解。
代码块1:resolveBeforeInstantiation
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.
// 1.mbd不是合成的,并且BeanFactory中存在InstantiationAwareBeanPostProcessor
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
// 2.解析beanName对应的Bean实例的类型
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
// 3.实例化前的后置处理器应用(处理InstantiationAwareBeanPostProcessor)
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
// 4.如果返回的bean不为空,会跳过Spring默认的实例化过程,
// 所以只能在这里调用BeanPostProcessor实现类的postProcessAfterInitialization方法
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
// 5.如果bean不为空,则将beforeInstantiationResolved赋值为true,代表在实例化之前已经解析
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}
3.实例化前的后置处理器应用,见代码块2详解。
4.实例化后的后置处理器应用,见 Spring IoC:getBean详解 中的代码块4。
代码块2:applyBeanPostProcessorsBeforeInstantiation
protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
// 1.遍历当前BeanFactory中的BeanPostProcessor
for (BeanPostProcessor bp : getBeanPostProcessors()) {
// 2.应用InstantiationAwareBeanPostProcessor后置处理器,允许postProcessBeforeInstantiation方法返回bean对象的代理
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
// 3.执行postProcessBeforeInstantiation方法,在Bean实例化前操作,
// 该方法可以返回一个构造完成的Bean实例,从而不会继续执行创建Bean实例的“正规的流程”,达到“短路”的效果。
Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
if (result != null) {
// 4.如果result不为空,也就是有后置处理器返回了bean实例对象,则会跳过Spring默认的实例化过程
return result;
}
}
}
return null;
}
在实例化之前执行 InstantiationAwareBeanPostProcessor 的 postProcessBeforeInstantiation 方法,该方法可以返回 bean 实例的代理,从而跳过 Spring 默认的实例化过程。
代码块3:doCreateBean
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
throws BeanCreationException {
// Instantiate the bean.
// 1.新建Bean包装类
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
// 2.如果是FactoryBean,则需要先移除未完成的FactoryBean实例的缓存
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 3.根据beanName、mbd、args,使用对应的策略创建Bean实例,并返回包装类BeanWrapper
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
// 4.拿到创建好的Bean实例
final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
// 5.拿到Bean实例的类型