【spring源码】Spring中BeanPostProcessor何时生效
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2022-07-14 16:13:53
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Spring中BeanPostProcessor何时生效
在Spring中我们有时会使用BeanPostProcessor来增强我们的bean,但BeanPostProcessor又是什么时候被使用的呢,接下来我们一起来跟着spring的源码走一下
1.编写一个入口类
public class Entry {
public static void main(String[] args) {
ApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class);
}
}
2. 点击进入构造方法
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
//1. 在此处向BeanDefinition中注册了6个注解处理器
//2. 此处初始化了系统属性以及环境变量
//3. 注册了注解过滤器
this();
//紧紧注册配置类的BeanDefinition信息到BeanFactory
register(annotatedClasses);
//真正创建对象并调用BeanPostProcessor处理器的方法
refresh();
}
3. 进入refresh方法
- 此处找到方法中的finishBeanFactoryInitialization,这里就是具体实列化Bean的地方
@Override
public void refresh() throws BeansException, IllegalStateException {
.....................
try {
.....................
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
...................
}
4. 进入finishBeanFactoryInitialization方法
- 此处最后一行方法为初始化Bean,找到该方法的实现类DefaultListableBeanFactory并进入方法
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
...................
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}
5. preInstantiateSingletons方法中
- 最后一个else中的getBean为具体创建Bean代码,点击进入并进入doGetBean方法
public void preInstantiateSingletons() throws BeansException {
.....................
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
getBean(beanName);
}
}
}
6.AbstractBeanFactory类的doGetBean方法中
- 找到314-328行代码中的createBean方法
// 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);
}
7.找到AbstractAutowireCapableBeanFactory类
- 在此类中找到createBean方法,再次方法中可以找到doCreateBean方法调用
try {
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
8.AbstractAutowireCapableBeanFactory
- 在此类中的doCreateBean方法里面我们可以找到如下代码
// Initialize the bean instance.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
9.进入AbstractAutowireCapableBeanFactory类
- 在方法initializeBean中可以找到applyBeanPostProcessorsBeforeInitialization方法调用
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
10. 方法applyBeanPostProcessorsBeforeInitialization就是所有的增强处理的地方
@Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
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