以下源码基于 Spring 5.2.8.RELEASE 版本.
BeanPostProcessor有2个方法,分别是在自定义初始化之前和之后执行的行为.
这是Spring框架中非常重要的一个接口,Spring的AOP也是基于该接口的AbstractAdvisingBeanPostProcessor的抽象实现,其基于观察者设计模式,将需要运用AOP的类的代理添加到观察者的对象列表中,当执行到对应方法,由生成的代理方法去通知观察者然后执行后续行为.
不过AOP考虑其他文章来讲述.
InitializingBean只有一个方法,用于BeanFactory完成属性设置之后,执行自定义的初始化行为.
postProcessBeforeInitialization(Object bean, String beanName)方法会在Bean被Spring容器初始化时使用(在被管理的对象实例化后,由Spring容器进行的注入过程),2个参数分别是当前的bean实例及bean的名字.
看下Bean初始化的方法:
// Spring容器初始化bean
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
// 执行对应的Aware接口的方法,将需要预先准备的信息
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 在执行InitializingBean方法之前的处理
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 执行InitializingBean初始化方法
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
// 在执行InitializingBean方法之后的处理
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
// Spring容器执行Bean实现的Aware的相关方法,将资源注入
private void invokeAwareMethods(final String beanName, final Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
// Bean在执行初始化方法前,执行BeanPostProcessor的postProcessBeforeInitialization
@Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
// getBeanPostProcessors()返回所有的在Spring容器注册的BeanPostProcessor实现类
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
// Bean在执行初始化方法后,执行BeanPostProcessor的postProcessAfterInitialization
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
// getBeanPostProcessors()返回所有的在Spring容器注册的BeanPostProcessor实现类
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
// Bean的自定义初始化方法
protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
throws Throwable {
// 是否实现了InitializingBean
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isTraceEnabled()) {
logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
((InitializingBean) bean).afterPropertiesSet();
return null;
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
// 设置属性
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null && bean.getClass() != NullBean.class) {
String initMethodName = mbd.getInitMethodName();
if (StringUtils.hasLength(initMethodName) &&
!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
接下来写个例子检查:
package org.lionzhou.spring;
import lombok.Data;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class BeanPostProcessorApp {
static class MyBeanPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
// 检查对象类型
if (bean instanceof BeanOne) {
System.out.println(String.format("before bean %s (%s)", beanName, bean.toString()));
final BeanOne beanOne = (BeanOne) bean;
// 对属性自增100
beanOne.setNo(beanOne.getNo() + 100);
}
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
// 答应结果
if (bean instanceof BeanOne) {
System.out.println(String.format("after bean %s (%s)", beanName, bean.toString()));
}
return bean;
}
}
@Data
static class BeanOne implements InitializingBean {
private Integer no = 100;
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("from afterPropertiesSet.");
}
}
public static void main(String[] args) {
final AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
context.register(BeanOne.class);
final ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
// 注册BeanPostProcessor
beanFactory.addBeanPostProcessor(new MyBeanPostProcessor());
context.refresh();
// 内部静态类,所以bean的默认生成的名字需要外部对象名
final BeanOne beanOne = beanFactory.getBean("beanPostProcessorApp.BeanOne", BeanOne.class);
System.out.println(beanOne);
}
}
before bean beanPostProcessorApp.BeanOne (BeanPostProcessorApp.BeanOne(no=100))
from afterPropertiesSet.
after bean beanPostProcessorApp.BeanOne (BeanPostProcessorApp.BeanOne(no=200))
BeanPostProcessorApp.BeanOne(no=200)