Spring中bean的生命周期(通俗易懂)

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");}@Overridepublic void setBeanName(String s) {System.out.println("初始化-setBeanName");}@Overridepublic void setBeanFactory(BeanFactory beanFactory) throws BeansException {System.out.println("初始化-setBeanFactory");}@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {System.out.println("初始化-setApplicationContext");}@Overridepublic 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。