spring源码解析一：bean

学习spring源码是一件非常煎熬且很有挑战的事情，在我们日常的工作中用的最多的框架可能就是spring及其的拓展，这是一个极其庞大的家族，首先我们来先来学习spring源码，然后在它的基础上学习spring mvc ,springboot,spring colud等。

1、 BeanFactory 对bean的生命周期进行管理，生产各种所需要的bean供我们使用

BeanFactory是一个接口，它的子接口跟实现有：AnnotationConfigApplicationContext 是用来管理注解bean的容器；GenericApplicationContext 通用应用上下文； AnnotationConfigRegistry 注解配置注册表，ListableBeanFactory根据各种条件获取bean的配置清单；ConfigurableBeanFactory提供配置factory的各种方法

2、BeanFactoryPostProcessor:对beanFactory进行操作更新的类；

@FunctionalInterface
public interface BeanFactoryPostProcessor {


  /**
   * Modify the application context's internal bean factory after its standard
   * initialization. All bean definitions will have been loaded, but no beans
   * will have been instantiated yet. This allows for overriding or adding
   * properties even to eager-initializing beans.
   * @param beanFactory the bean factory used by the application context
   * @throws org.springframework.beans.BeansException in case of errors
   */
  void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;


}

BeanFactoryPostProcessor 就一个方法 postProcessBeanFactory，看一下他的实现ConfigurationClassPostProcessor

class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
    PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {

ConfigurationClassPostProcessor 实现了好几个接口，我们简单说一下：BeanDefinitionRegistryPostProcessor：BeanFactoryPostProcessor的子接口，在常规的BeanFactoryPostProcessor检测之前注册bean的定义信息

PriorityOrdered：设置优先级

ResourceLoaderAware：设置资源加载器，可以获取到外部资源文件

BeanClassLoaderAware：设置类加载器

EnvironmentAware：设置环境变量

/**
   * 添加CGLIB增强处理及ImportAwareBeanPostProcessor后置处理类
   *
   * Prepare the Configuration classes for servicing bean requests at runtime
   * by replacing them with CGLIB-enhanced subclasses.
   */
  @Override
  public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    int factoryId = System.identityHashCode(beanFactory);
    if (this.factoriesPostProcessed.contains(factoryId)) {
      throw new IllegalStateException(
          "postProcessBeanFactory already called on this post-processor against " + beanFactory);
    }
    this.factoriesPostProcessed.add(factoryId);
    if (!this.registriesPostProcessed.contains(factoryId)) {


//构建和验证一个类是否被@Configuration修饰，并做相关的解析工作
      processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
    }
  //增强配置
    enhanceConfigurationClasses(beanFactory);
    //添加后置处理类
    beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
  }

3、BeanDefinition:bean的定义描述信息；

从加载配置文件后生成bean定义信息，主要就是设置类名，作用域，单例还是原型，是否懒加载等

4、 beanPostProcessor:对初始化前后进行处理的类；

主要就两个方法

public interface BeanPostProcessor {


   /**
    * 初始化方法调用前要进行的处理逻辑
    *
    * Apply this {@code BeanPostProcessor} to the given new bean instance before any bean
    * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
    * or a custom init-method). The bean will already be populated with property values.
    * The returned bean instance may be a wrapper around the original.
    * 
The default implementation returns the given {@code bean} as-is.
    * @param bean the new bean instance
    * @param beanName the name of the bean
    * @return the bean instance to use, either the original or a wrapped one;
    * if {@code null}, no subsequent BeanPostProcessors will be invoked
    * @throws org.springframework.beans.BeansException in case of errors
    * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
    */
   @Nullable
   default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
      return bean;
   }


   /**
    * 在初始化方法指定后要进行的处理逻辑
    *
    * Apply this {@code BeanPostProcessor} to the given new bean instance after any bean
    * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
    * or a custom init-method). The bean will already be populated with property values.
    * The returned bean instance may be a wrapper around the original.
    * 
In case of a FactoryBean, this callback will be invoked for both the FactoryBean
    * instance and the objects created by the FactoryBean (as of Spring 2.0). The
    * post-processor can decide whether to apply to either the FactoryBean or created
    * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
    * 
This callback will also be invoked after a short-circuiting triggered by a
    * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
    * in contrast to all other {@code BeanPostProcessor} callbacks.
    * 
The default implementation returns the given {@code bean} as-is.
    * @param bean the new bean instance
    * @param beanName the name of the bean
    * @return the bean instance to use, either the original or a wrapped one;
    * if {@code null}, no subsequent BeanPostProcessors will be invoked
    * @throws org.springframework.beans.BeansException in case of errors
    * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
    * @see org.springframework.beans.factory.FactoryBean
    */
   @Nullable
   default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
      return bean;
   }

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