具体流程

  bean的生命周期分4个阶段：
  1.实例化
  2.属性赋值
  3.初始化
  4.销毁

  实例化就是在内存中new()出一个对象，属性赋值就是给那些被@Autowired修饰的属性注入对象，销毁是在Spring容器关闭时触发，初始化的步骤比较多：

  1.是否实现Aware的相关接口，调用重载方法
  (BeanNameAware#setBeanName，
  BeanClassLoaderAware#setBeanClassLoader，
  BeanFactoryAware#setBeanFactory，
  ApplicationContextAware#setApplicationContext)

  2.是否有bean实现BeanPostProcessor接口，调用实现的postProcessBeforeInitialization方法(实现类加载时不调用自身实现的方法，调用其他实现类的)

  3.是否实现InitializingBean接口，调用重载方法afterPropertiesSet方法

  4.是否指定@Bean的initMethod属性，调用指定的方法(定义在bean对应的类里，不是配置类里)

  5.是否有bean实现BeanPostProcessor接口，调用实现的postProcessAfterInitialization方法(和第2点同理)

  话不多说，下面用代码来给出示例。

代码示例

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class A implements BeanNameAware, BeanFactoryAware, 
             ApplicationContextAware, InitializingBean {

    public A() {
        System.out.println("a的构造函数");
    }

    @Override
    public void setBeanName(String s) {
        System.out.println("初始化-setBeanName");
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) 
                throws BeansException {
        System.out.println("初始化-setBeanFactory");
    }

    @Override
    public void setApplicationContext(ApplicationContext 
                applicationContext) throws BeansException {
        System.out.println("初始化-setApplicationContext");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("初始化-afterPropertiesSet");
    }

    public void init() {
        System.out.println("初始化-init");
    }

}

import org.springframework.context.annotation.Bean;

public class MyConfiguration  {

    @Bean(initMethod = "init")
    public A a() {
        return new A();
    }

}

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Import;

@Import(MyConfiguration.class)
public class BootStrap {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = 
        new AnnotationConfigApplicationContext(BootStrap.class);
        A bean = context.getBean(A.class);
    }
	
}

  运行启动类后，控制台打印：

  这里单独再说下BeanPostProcessor，A类去实现它：

public class A implements BeanNameAware, BeanFactoryAware, 
             ApplicationContextAware, InitializingBean, BeanPostProcessor{
             
    //...
    //其余的方法不动，就添加下面2个方法
    public Object postProcessBeforeInitialization(Object bean, 
                  String beanName) throws BeansException {
        System.out.println(beanName + "：初始化-beforeInitialization");
        return bean;
    }

	public Object postProcessAfterInitialization(Object bean, 
                  String beanName) throws BeansException {
        System.out.println(beanName + "：初始化-afterInitialization");
        return bean;
    }

}

  再次运行启动类，控制台和之前的一样(A这个bean的初始化，没有调用实现的那2个方法)：

  A类还原，不实现BeanPostProcessor；MyConfiguration类实现该接口：

import org.springframework.context.annotation.Bean;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

public class MyConfiguration implements BeanPostProcessor {

    @Bean(initMethod = "init")
    public A a() {
        return new A();
    }

    public Object postProcessBeforeInitialization(Object bean, 
                  String beanName) throws BeansException {
        System.out.println(beanName + "：初始化-beforeInitialization");
        return bean;
    }

    public Object postProcessAfterInitialization(Object bean, 
                  String beanName) throws BeansException {
        System.out.println(beanName + "：初始化-afterInitialization");
        return bean;
    }
    
}

  再次运行启动类，这时想要的效果有了：

  所以bean初始化中，不会调用自身实现BeanPostProcessor接口的那2个方法，调用其他实现BeanPostProcessor接口的bean的。