springboot @configuration注解的配置， @bean注解方法a, 在@bean注解 getb（）{}需要注入a

深度解析@Configuration注解

/*** General purpose AOP callback. Used when the target is dynamic or when the* proxy is not frozen.*/private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {private final AdvisedSupport advised;public DynamicAdvisedInterceptor(AdvisedSupport advised) {this.advised = advised;}@Override@Nullablepublic Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {Object oldProxy = null;boolean setProxyContext = false;Object target = null;TargetSource targetSource = this.advised.getTargetSource();try {if (this.advised.exposeProxy) {// Make invocation available if necessary.oldProxy = AopContext.setCurrentProxy(proxy);setProxyContext = true;}// Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...target = targetSource.getTarget();Class<?> targetClass = (target != null ? target.getClass() : null);// advisor增强List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);Object retVal;// Check whether we only have one InvokerInterceptor: that is,// no real advice, but just reflective invocation of the target.if (chain.isEmpty() && CglibMethodInvocation.isMethodProxyCompatible(method)) {// We can skip creating a MethodInvocation: just invoke the target directly.// Note that the final invoker must be an InvokerInterceptor, so we know// it does nothing but a reflective operation on the target, and no hot// swapping or fancy proxying.Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);retVal = invokeMethod(target, method, argsToUse, methodProxy);}else {// We need to create a method invocation... // advisor调用链retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();}retVal = processReturnType(proxy, target, method, retVal);return retVal;}finally {if (target != null && !targetSource.isStatic()) {targetSource.releaseTarget(target);}if (setProxyContext) {// Restore old proxy.AopContext.setCurrentProxy(oldProxy);}}}@Overridepublic boolean equals(@Nullable Object other) {return (this == other ||(other instanceof DynamicAdvisedInterceptor &&this.advised.equals(((DynamicAdvisedInterceptor) other).advised)));}/*** CGLIB uses this to drive proxy creation.*/@Overridepublic int hashCode() {return this.advised.hashCode();}}

aop和cglib

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;@Configuration
public class AppConfig {/**
cglib重写方法
/@Beanpublic A a() {return new A();}/**
cglib重写方法
/@Bean
public B b() {
/**
调用cglib重写的a方法
/return new B(a());
}
}

使用 enhancer 对 configClass 进行增强处理，得到增强后的类 enhancedClass。

如果 enhancedClass 与 configClass 不同，意味着类被增强，将用增强后的类替换原有类。

beanDef.setBeanClass(enhancedClass);// 在beanDefinition替换掉class

public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {.....// 如果指定属性是full, 则进行下面处理，该属性在前面阶段设置if (ConfigurationClassUtils.CONFIGURATION_CLASS_FULL.equals(configClassAttr)) {if (!(beanDef instanceof AbstractBeanDefinition)) {throw new BeanDefinitionStoreException("Cannot enhance @Configuration bean definition '" +beanName + "' since it is not stored in an AbstractBeanDefinition subclass");}else if (logger.isInfoEnabled() && beanFactory.containsSingleton(beanName)) {logger.info("Cannot enhance @Configuration bean definition '" + beanName +"' since its singleton instance has been created too early. The typical cause " +"is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor " +"return type: Consider declaring such methods as 'static'.");}// 加入到增强集合中configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);}}if (configBeanDefs.isEmpty() || NativeDetector.inNativeImage()) {// nothing to enhance -> return immediatelyenhanceConfigClasses.end();return;}// 新建增强器ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();// 遍历待增强的容器列表for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {AbstractBeanDefinition beanDef = entry.getValue();// If a @Configuration class gets proxied, always proxy the target classbeanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);// Set enhanced subclass of the user-specified bean classClass<?> configClass = beanDef.getBeanClass();// 进行增强处理Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);if (configClass != enhancedClass) {if (logger.isTraceEnabled()) {logger.trace(String.format("Replacing bean definition '%s' existing class '%s' with " +"enhanced class '%s'", entry.getKey(), configClass.getName(), enhancedClass.getName()));}beanDef.setBeanClass(enhancedClass);}}enhanceConfigClasses.tag("classCount", () -> String.valueOf(configBeanDefs.keySet().size())).end();}