【Spring高级】第3讲 Bean的生命周期

基本的生命周期

为了演示生命周期的过程，我们直接使用 SpringApplication.run()方法，他会直接诶返回一个容器对象。

import org.springframework.boot.SpringApplication;
import org.springframework.context.ConfigurableApplicationContext;@SpringBootApplication
public class BeanLifecycleTest {public static void main(String[] args) {ConfigurableApplicationContext context = SpringApplication.run(BeanLifecycleTest.class, args);context.close();}
}

然后定义一个Bean，如下：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;@Component
public class LifeCycleBean {public LifeCycleBean() {System.out.println("构造方法");}/*** 依赖注入方法* 当参数是一个对象时，可以直接注入* 但是如果是String类型，则需要使用@Value，找到环境变量JAVA_HOME** @param home*/@Autowiredpublic void autowired(@Value("${JAVA_HOME}") String home) {System.out.println("依赖注入");}/***  @PostConstruct 用来标记 bean 初始化完成后的回调方法*/@PostConstructpublic void init() {System.out.println("初始化");}/*** @PreDestroy 用来标记 bean 销毁前的回调方法*/@PreDestroypublic void destory() {System.out.println("销毁");}}

上面的LifeCycleBean我们定义了构造方法、初始化方法、依赖注入方法、销毁方法。

启动应用，打印如下：

构造方法
依赖注入
初始化
2024-02-29 22:53:29.169  INFO 39870 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2024-02-29 22:53:29.182  INFO 39870 --- [           main] c.c.demo02.chapter03.BeanLifecycleTest   : Started BeanLifecycleTest in 1.724 seconds (JVM running for 7.593)
2024-02-29 22:53:29.191  INFO 39870 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
销毁

上面就可以看出整个流程。

后处理器

除了基本的生命周期，下面看下加上后处理器后的流程。

import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.stereotype.Component;@Component
public class MyBeanPostProcessor implements InstantiationAwareBeanPostProcessor, DestructionAwareBeanPostProcessor {@Overridepublic void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean")) {System.out.println("<<<<< postProcessBeforeDestruction 销毁之前执行");}}@Overridepublic Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean")) {System.out.println("<<<<< postProcessBeforeInstantiation 实例化之前执行");}return null;
//        return InstantiationAwareBeanPostProcessor.super.postProcessBeforeInstantiation(beanClass, beanName);}@Overridepublic boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean")) {System.out.println("<<<<< postProcessBeforeInstantiation 实例化之后执行");}// 如果返回false会跳过依赖注入阶段return true;
//        return InstantiationAwareBeanPostProcessor.super.postProcessAfterInstantiation(bean, beanName);}@Overridepublic PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {//  依赖注入阶段执行，如@Autowired，@Value @Resourceif (beanName.equals("lifeCycleBean")) {System.out.println("<<<<< postProcessProperties 依赖注入阶段执行");}return null;
//        return InstantiationAwareBeanPostProcessor.super.postProcessProperties(pvs, bean, beanName);}@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {// 初始化之前执行，如@PostConstruct，@ConfigurationPropertiesif (beanName.equals("lifeCycleBean")) {System.out.println("<<<<< postProcessBeforeInitialization 初始化之前执行");}return null;
//        return InstantiationAwareBeanPostProcessor.super.postProcessBeforeInitialization(bean, beanName);}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {// 一般这个阶段是替换掉原有的bean，代替增强if (beanName.equals("lifeCycleBean")) {System.out.println("<<<<< postProcessAfterInitialization 初始化之后执行");}return null;
//        return InstantiationAwareBeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);}
}

再次执行，结果如下

<<<<< postProcessBeforeInstantiation 实例化之前执行
构造方法
<<<<< postProcessBeforeInstantiation 实例化之后执行
<<<<< postProcessProperties 依赖注入阶段执行
依赖注入
<<<<< postProcessBeforeInitialization 初始化之前执行
<<<<< postProcessAfterInitialization 初始化之后执行
2024-02-29 23:47:57.110  INFO 42057 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2024-02-29 23:47:57.145  INFO 42057 --- [           main] c.c.demo02.chapter03.BeanLifecycleTest   : Started BeanLifecycleTest in 2.242 seconds (JVM running for 8.116)
2024-02-29 23:47:57.158  INFO 42057 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
<<<<< postProcessBeforeDestruction 销毁之前执行
销毁

通过上面可以看出，各个后置处理器分别作用在Bean生命周期的哪个阶段了。

总结

基本生命周期

创建前后的增强

postProcessBeforeInstantiation：这里返回的对象若不为 null 会替换掉原本的 bean，并且仅会走 postProcessAfterInitialization 流程
postProcessAfterInstantiation：这里如果返回 false 会跳过依赖注入阶段

依赖注入前的增强

postProcessProperties：如 @Autowired、@Value、@Resource

初始化前后的增强

postProcessBeforeInitialization：这里返回的对象会替换掉原本的 bean，如 @PostConstruct、@ConfigurationProperties
postProcessAfterInitialization ：这里返回的对象会替换掉原本的 bean，如代理增强

销毁之前的增强