Spring源码解析之Configuration

一、@Configuration

1.1 未加@Configuration

<!--logback-test.xml，配置不打印日志-->
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
   <include resource="org/springframework/boot/logging/logback/base.xml" />
   <logger name="org.springframework" level="OFF"/>
</configuration>

1.2 加上@Configuration

1.3 Cglib *

二、源码跟踪

2.1 AnnotationConfigApplicationContext

2.2 AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(Class<?>... annotatedClasses)

2.3 AbstractApplicationContext#refresh()

@Override
public void refresh() throws BeansException, IllegalStateException {
// 同步，线程安全； 防止 fresh还没结束  就又进入改方法 导致容器初始化错乱
synchronized (this.startupShutdownMonitor) {
// 准备刷新 记录开始时间  设置几个标志位  验证环境属性
prepareRefresh();

// 告诉子类刷新内部bean工厂  创建BeanFactory  并且获取BeanDefinition的定义信息
/**
*obtainFreshBeanFactory();方法
*解析为一个个beanDefinition 放在我们beanDefinitionMap中管理起来
*  1. refreshBeanFactory(); 核心方法
* AbstractRefreshableApplicationContext#refreshBeanFactory()
* 创建DefaultListableBeanFactory 并设置属性
* 加载BeanFactory； 根据不同的类型，调用不同的方法
* org.springframework.context.support.AbstractXmlApplicationContext#loadBeanDefinitions(org.springframework.beans.factory.support.DefaultListableBeanFactory)
*/
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

// 准备在这种情况下使用的bean工厂  向beanFactory中设置一些属性  。对BeanFactory 进行各种功能填充
prepareBeanFactory(beanFactory);

try {
// 允许在上下文 的子类中对bean工厂进行后处理  由子类去实现； 主要是自定义去使用
postProcessBeanFactory(beanFactory);

// 第5步 【BeanFactoryPostProcessors ;bean工厂后置处理器】调用我们的bean工厂后置处理器 (所有实现接口BeanFactoryPostProcessor接口的)
//主要是
// 会在此将class扫描成BeanDefinition 并注册bean 到一个BeanDefinitionMap中 这个过程使用到代理
//BeanFactoryPostProcessor 可以 用于容器完成初始化()
// 此处可以 还没有实例化Bean之前读取Bean的信息，并作出一些修改。
// 例如修改Bean的属性，修改Bean的scope等
invokeBeanFactoryPostProcessors(beanFactory);

//https://blog.csdn.net/caihaijiang/article/details/35552859
// 【BeanPostProcessors ;bean后置处理器】 注册BeanPostProcessor
// BeanPostProcessor是Bean的后置处理器，
// 在Bean的初始化方法[InitializingBean 以及init-method]前，后执行。
registerBeanPostProcessors(beanFactory);

// 为上下文初始化Message 源， 即不同语言的消息体， 国际化处理 i18n
initMessageSource();

// 初始化事件传播器
//初始化应用消息广播器， 并放入"applicationEventMulticaster" bean 中
initApplicationEventMulticaster();

// 扩展的一个实现 ，留给子类来初始化其它的Bean。如springboot内嵌的tomcat在这个阶段完成
onRefresh();

// 注册 *
// 在所有注册的bean 中查找Listener bean ， 注册到消息广播报中
registerListeners();

/**第11步
对于非抽象类、非延迟初始化的单例bean，
在spring容器启动的时候调用getBean方法来实例化bean， 并进行相关初始化工作，
getBean方法最终调用AbstractAutowireCapableBeanFactory.doCreateBean方法
*/
// 在创建BeanFactory的过程中，BeanDefinition注册到了BeanFactory中的一个ConCurretHashMap对象中
// 以BeanName为key，BeanDefinition为value ； 实例化所有剩余的（非延迟初始化）单例。
finishBeanFactoryInitialization(beanFactory);

// 第12步 最后一步：发布相应的事件。
//完成刷新过程， 通知生命周期处现器lifecycleProcessor 刷新过程， 同时发出ContextRefreshEvent 通知别人
finishRefresh();
}

catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}

// 第13步 销毁以创建的Bean
destroyBeans();

//取消refresh操作，重置容器的同步标识
cancelRefresh(ex);

// Propagate exception to caller.
throw ex;
}

finally {
resetCommonCaches();
}
}
}

2.4 AbstractApplicationContext#invokeBeanFactoryPostProcessors

2.5 PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

Set<String> processedBeans = new HashSet<>();

// 对BeanDefinitionRegistry 类型的处理
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// 用于存放BeanDefinitionRegistryPostProcessor
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

// 遍历所有的beanFactoryPostProcessors，将BeanDefinitionRegistryPostProcessor和普通BeanFactoryPostProcessor区分开
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
/**
对于BeanDefinitionRegistryPostProcessor 类型， 在BeanFactoryPostProcessor 的
基础上还有自己定义的方法，需要先调用
*/
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
// 记录常规BeanFactoryPostProcessor
regularPostProcessors.add(postProcessor);
}
}

/**
不要在这里初始化FactoryBeans: 我们需要保留所有常规bean未初始化，让bean工厂后处理器应用到它们!
BeanDefinitionRegistryPostProcessors之间的分离实现排好序，点好，等等。
获取spring配置文件中定义的所有实现BeanFactoryPostProcessor接口的bean，然后根据优先级进行排序
*/
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

// 首先，调用实现优先排序的BeanDefinitionRegistryPostProcessors
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// PriorityOrdered.class 优先排序
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();

// 接下来，调用实现Ordered的BeanDefinitionRegistryPostProcessors
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// Ordered.class
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();

// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
}

// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
// 调用ConfigurationClassPostProcessor#postProcessBeanFactory增强配置类
// 通过cglib生成增强类
// 设置beanDefinition的beanClass为增强类，让@Bean生成的bean是单例
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}

else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}

// BeanFactoryPostProcessor.class类型
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// 筛选出bean工程中存在的所有实现BeanFactoryPostProcessor类的类名称

// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
// 已经存在了，不再处理
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
// 为PriorityOrdered类型
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
// 为Ordered类型
orderedPostProcessorNames.add(ppName);
}
else {
// 这个就是我们当前需要关心的PostProcessors
//nonOrderedPostProcessors添加的不是bean实例，而是BeanDefinition
nonOrderedPostProcessorNames.add(ppName);
}
}

// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

// Finally, invoke all other BeanFactoryPostProcessors.
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
beanFactory.clearMetadataCache();
}

2.6 PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

2.7 ConfigurationClassPostProcessor#postProcessBeanFactory

2.8 ConfigurationClaassPostProcessor#enhanceConfigurationClasses

public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {
Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<>();
for (String beanName : beanFactory.getBeanDefinitionNames()) {
BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);
// 判断是否是一个全注解类
// 扫描是全注解类？full和lite的关系
if (ConfigurationClassUtils.isFullConfigurationClass(beanDef)) {
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'.");
}
// 是全注解，需要代理，添加到configBeanDefs中
configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);
}
}
if (configBeanDefs.isEmpty()) {
// nothing to enhance -> return immediately
return;
}

ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
// 遍历这个map
for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
AbstractBeanDefinition beanDef = entry.getValue();
// If a @Configuration class gets proxied, always proxy the target class
beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
try {
// Set enhanced subclass of the user-specified bean class
Class<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader);
if (configClass != null) {
// 进行cglib代理，为@Configuration注解的类生成增强类
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()));
}
// 再通过beanDef.setBeanClass(enhancedClass)修改beanDefinition的BeanClass属性，
// 在bean实例化阶段，会利用反射技术将beanClass属性对应的类实例化出来
// 所以最终实例化出来的@Configuration bean是一个代理类的实例
beanDef.setBeanClass(enhancedClass);
}
}
}
catch (Throwable ex) {
throw new IllegalStateException("Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
}
}

2.9 ConfigurationClassUtils#checkConfigurationClassCandidate

1.在ConfigurationClassUtils类中的checkConfigurationClassCandidate标记是Full @Configuration还是lite @Bean mode

2.通过"full".equals(configClassAttr)判断是否是全类注解是全注解

3.则将beandefinition放入map中configBeanDefs.put

4.遍历这个map

5.使用cglib技术为配置类生成一个enhancedClass

6.通过enhancer.enhance进行cglib代理，为@Configuration注解的类生成增强类

7.再通过beanDef.setBeanClass(enhancedClass)修改beanDefinition的BeanClass属性，在bean实例化阶段，会利用反射技术将beanClass属性对应的类实例化出来，所以最终实例化出来的@Configuration bean是一个代理类的实例

使用了@Configuration注解的类，属于Full @Configuration。@Configuration类允许通过调用同一类中的其他@Bean方法来定义bean之间的依赖关系，保证@Bean的对象作用域受到控制，避免多例。

@Configuration类中的@Bean地方会被CGLIB进行代理。Spring会拦截该方法的执行，在默认单例情况下，容器中只有一个Bean，所以我们多次调用user()方法，获取的都是同一个对象。

对于@Configuration注解的类中@Bean标记的方法，返回的都是一个bean，在增强的方法中，Spring会先去容器中查看一下是否有这个bean的实例了，如果有了的话，就返回已有对象，没有的话就创建一个，然后放到容器中。

2.10 ConfigurationClassEnhancer#enhance

2.11 ConfigurationClassEnhancer#newEnhancer

2.12 ConfigurationClassEnhancer#CallBacks

2.13 ConfigurationClassEnhancer#intercept

2.13.1 ConfigurationClassEnhancer#isCurrentlyInvokedFactoryMethod

2.14 ConfigurationClassEnhancer#resolveBeanReference

private Object resolveBeanReference(Method beanMethod, Object[] beanMethodArgs,
ConfigurableBeanFactory beanFactory, String beanName) {

// The user (i.e. not the factory) is requesting this bean through a call to
// the bean method, direct or indirect. The bean may have already been marked
// as 'in creation' in certain autowiring scenarios; if so, temporarily set
// the in-creation status to false in order to avoid an exception.
// 判断他是否正在创建
boolean alreadyInCreation = beanFactory.isCurrentlyInCreation(beanName);
try {
if (alreadyInCreation) {
beanFactory.setCurrentlyInCreation(beanName, false);
}
boolean useArgs = !ObjectUtils.isEmpty(beanMethodArgs);
if (useArgs && beanFactory.isSingleton(beanName)) {
// Stubbed null arguments just for reference purposes,
// expecting them to be autowired for regular singleton references?
// A safe assumption since @Bean singleton arguments cannot be optional...
for (Object arg : beanMethodArgs) {
if (arg == null) {
useArgs = false;
break;
}
}
}
Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) :
beanFactory.getBean(beanName));
if (!ClassUtils.isAssignableValue(beanMethod.getReturnType(), beanInstance)) {
// Detect package-protected NullBean instance through equals(null) check
if (beanInstance.equals(null)) {
if (logger.isDebugEnabled()) {
logger.debug(String.format("@Bean method ％s.％s called as bean reference " +
"for type [％s] returned null bean; resolving to null value.",
beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),
beanMethod.getReturnType().getName()));
}
beanInstance = null;
}
else {
String msg = String.format("@Bean method ％s.％s called as bean reference " +
"for type [％s] but overridden by non-compatible bean instance of type [％s].",
beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),
beanMethod.getReturnType().getName(), beanInstance.getClass().getName());
try {
BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName);
msg += " Overriding bean of same name declared in: " + beanDefinition.getResourceDescription();
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore - simply no detailed message then.
}
throw new IllegalStateException(msg);
}
}
Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod();
if (currentlyInvoked != null) {
String outerBeanName = BeanAnnotationHelper.determineBeanNameFor(currentlyInvoked);
beanFactory.registerDependentBean(beanName, outerBeanName);
}
return beanInstance;
}
finally {
if (alreadyInCreation) {
beanFactory.setCurrentlyInCreation(beanName, true);
}
}
}

三、总结

•  lite @Bean mode ：当@Bean方法在没有使用@Configuration注解的类中声明时称之为lite @Bean mode

• Full @Configuration：如果@Bean方法在使用@Configuration注解的类中声明时称之为Full @Configuration
  

Full @Configuration中的@Bean方法会被CGLIB所代理，而 lite @Bean mode中的@Bean方法不会被CGLIB代理

@Configuration注解作用

1.告诉spring这是一个配置类，相当于spring的xml配置文件

2.被@Configuration 注解的类，会被cglib代理进行增强

3.@Configuration类允许通过调用同一类中的其他@Bean方法来定义bean之间的依赖关系，保证@Bean的对象作用域受到控制，避免多例

@Configuration注解底层是如何实现的，通过源码咱们可以反推并总结为以下几点：

1.Spring首先会获取到所有的beanDefenition

2.ConfigurationClassUtils类中checkConfigurationClassCandidate方法判断是Full @Configuration还是lite @Bean mode

3.通过ConfigurationClassPostProcessor后置处理器遍历所有的beanDefenition

4.将标记了Full @Configuration模式的beanDefenition，会对这个类进行cglib代理，生成一个代理类，并把这个类设置到BeanDefenition的Class属性中

5.配置类会被CGLIB增强(生成代理对象)，放进IoC容器内的是代理

6.对于内部类是没有限制的：可以是Full模式或者Lite模式

7.配置类内部可以通过方法调用来处理依赖，并且能够保证是同一个实例，都指向IoC内的那个单例

8.需要用这个Bean实例的时候，从这个Class属性中拿到的Class对象进行反射，最终反射出来的是代理增强后的类

9.通过@Configuration标注类的Bean，Spring会先去容器中查看是否有这个Bean实例，如果有就返回已有的对象，没有就创建一个，然后放到容器中

来源：https://blog.csdn.net/qq_38826019/article/details/117134588