从哪里入手
当然是从注释开始
根据源码注释我们易得 AutowiredAnnotationBeanPostProcessor是Autowired的实现类,xxxBeanPostProcessor这不就是后置处理器吗我记得在哪里见过
我记得有个refresh()的方法 里面有注册BeanPostProcessor的操作,走进去瞧瞧
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
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...
resetCommonCaches();
}
}
}
战略断点1 registerBeanPostProcessors(beanFactory) 注册处理器
进入到org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors方法
经过一顿优先级排序操作,不绕弯直接看注册了哪些BeanPostProocessors
image-20191226153433012 默认有一个CommonAnnotationBeanPostProcessor处理器也被注册进来
战略断点2 finishBeanFactoryInitialization(beanFactory)
继续往后走我们直接走到关键的doCreateBean方法
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean
预解析过程
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// 省略...
// Allow post-processors to modify the merged bean definition.
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;
}
}
// 省略...
}
峰回路转 快走到调用的地方了
protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
// 校验是否MergedBeanDefinitionPostProcessor类型
if (bp instanceof MergedBeanDefinitionPostProcessor) {
MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
}
}
}
看下AutowiredAnnotationBeanPostProcessor继承关系
跳转到org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#postProcessMergedBeanDefinition
@Override
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
InjectionMetadata metadata = findAutowiringMetadata(beanName, beanType, null);
metadata.checkConfigMembers(beanDefinition);
}
这里完成对注入元素注解的预解析
属性注入过程
按照写代码的步骤,创建对象=>依赖对象创建=>赋值=>打工
我们直接调到org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
// 这里会走到AutowiredAnnotationBeanPostProcessor#postProcessProperties
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
}
为什么会走到AutowiredAnnotationBeanPostProcessor
继续往下看 具体属性的注入过程
@Override
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
try {
metadata.inject(bean, beanName, pvs);
}
// ... 省略
return pvs;
}
public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
Collection<InjectedElement> checkedElements = this.checkedElements;
Collection<InjectedElement> elementsToIterate =
(checkedElements != null ? checkedElements : this.injectedElements);
if (!elementsToIterate.isEmpty()) {
for (InjectedElement element : elementsToIterate) {
if (logger.isTraceEnabled()) {
logger.trace("Processing injected element of bean '" + beanName + "': " + element);
}
element.inject(target, beanName, pvs);
}
}
}
InjectedElement这个包含了多个注入实现对象,给我们设计自己业务代码也有很大的参考,比如签署合同,不同合同要素的注入,可以参考这种设计风格
技术总结
首先看到类名就要想到这个东西在哪产生,在哪调用,然后就能一步步找到答案;正所谓授人以鱼不如授人以渔
- 1.从注解注释的实现类,联想到refresh方法入口
- 2.找到注册的地方registerBeanPostProcessors
- 3.找到调用的地方finishBeanFactoryInitialization
- 4.找到最后属性复制的地点populateBean
给出一张图小结一下
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喜欢的可以一键三连,有问题欢迎在留言区评论
原文git
