@PostConstruct注解

@PostConstruct基本： @PostConstruct注解好多人以为是Spring提供的。其实是Java自己的注解。

Java中该注解的说明：@PostConstruct该注解被用来修饰一个非静态的void（）方法。被@PostConstruct修饰的方法会在服务器加载Servlet的时候运行，并且只会被服务器执行一次。PostConstruct在构造函数之后执行，init（）方法之前执行。

通常我们会是在Spring框架中使用到@PostConstruct注解 该注解的方法在整个Bean初始化中的执行顺序：

Constructor(构造方法) -> @Autowired(依赖注入) -> @PostConstruct(注释的方法)

应用：在静态方法中调用依赖注入的Bean中的方法。

package com.example.studySpringBoot.util;

import com.example.studySpringBoot.service.MyMethorClassService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

@Component public class MyUtils {

private static MyUtils          staticInstance = new MyUtils();
@Autowired
private MyMethorClassService    myService;
@PostConstruct
public void init(){
staticInstance.myService = myService;
}
public static Integer invokeBean(){
return staticInstance.myService.add(10,20);
}

} 那么Java提供的@PostConstruct注解，Spring是如何实现的呢？ 需要先学习下BeanPostProcessor这个接口：

public interface BeanPostProcessor {

/**
 * Apply this BeanPostProcessor to the given new bean instance <i>before</i> 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.
 * 
 * 任何Bean实例化，并且Bean已经populated(填充属性) 就会回调这个方法
 *
 */
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
/**

Apply this BeanPostProcessor to the given new bean instance <i>after</i> 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.

任何Bean实例化，并且Bean已经populated(填充属性) 就会回调这个方法


*/
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

那Spring初始化是那里回调这些方法呢？ 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，就是专门处理@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) ———————————————— 版权声明：本文为CSDN博主「那些很冒险的梦丶」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。 原文链接：https://blog.csdn.net/qq360694660/article/details/82877222