世上最全的@PostConstruct注解说明

@PostConstruct注意事项

1.@PostConstruct注解是java原生注解
            不是Spring提供的注解
2.@PostConstruct注解用于修饰非静态的void()方法
3.@PostConstruct修饰的方法会在服务器加载Servlet的时候运行,且只会被服务器运行一次
4.@PostConstruct修饰的方法在构造函数之后执行,init()方法之前运行

Spring中被@PostConstruct注解修饰的方法,运行顺序

Constructor(构造方法) -> @Autowired(依赖注入) -> @PostConstruct(注解的方法)

package com.java265.util;
 
import com.java265.service.MyMethorClassService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;
 
@Component
public class MyUtils {
 
    private static Utils  staticInstance = new Utils();
 
    @Autowired
    private MyMethorClassService    myService;
 
    @PostConstruct
    public void init(){
        staticInstance.myService = myService;
    }
 
    public static Integer invokeBean(){
        return staticInstance.myService.add(888,999);
    }
}

@PostConstruct注解如何被Spring运行呢？

Spring初始化回调方法的查找

AbstractApplicationContext.finishBeanFactoryInitialization(...);
    beanFactory.preInstantiateSingletons();
       DefaultlistableBeanFactory.getBean(beanName);
          AbstractBeanFactory.doGetBean();
            AbstractAutowireCapableBeanFactory.createBean(....)
                populateBean(beanName, mbd, instanceWrapper);
                initializeBean(...)
                 //调用BeanPostProcessor.postProcessBeforeInitialization()方法
                  applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
                 //调用BeanPostProcessor.postProcessBeforeInitialization()方法
                  applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
 

BeanPostProcessor有个实现类CommonAnnotationBeanPostProcessor
 用于处理@PostConstruct  @PreDestroy注解

CommonAnnotationBeanPostProcessor的父类InitDestroyAnnotationBeanPostProcessor()
 InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization()
    InitDestroyAnnotationBeanPostProcessor.findLifecycleMetadata()
            // 组装生命周期元数据
            InitDestroyAnnotationBeanPostProcessor.buildLifecycleMetadata()
            // 查找@PostConstruct注释的方法
            InitDestroyAnnotationBeanPostProcessor.initAnnotationType
            // 查找@PreDestroy注释方法
            InitDestroyAnnotationBeanPostProcessor.destroyAnnotationType
 
 // 反射调用          
 metadata.invokeInitMethods(bean, beanName);