Spring Bean的生命周期是面试过程中经常会问到的一道题目，为了不单纯的北宋八股文，还是决定自己去代码验证下答案的正确与否，同时加深自己对Spring Bean的认识。
首先，贴一下网上的答案：
Spring 中Bean 的生命周期
如上图所示，Bean 的生命周期还是比较复杂的，下面来对上图每一个步骤做文字描述:
1、Spring启动，查找并加载需要被Spring管理的bean，进行Bean的实例化
2、Bean实例化后对将Bean的引入和值注入到Bean的属性中
3、如果Bean实现了BeanNameAware接口的话，Spring将Bean的Id传递给setBeanName()方法
4、如果Bean实现了BeanFactoryAware接口的话，Spring将调用setBeanFactory()方法，将BeanFactory容器实例传入
5、如果Bean实现了ApplicationContextAware接口的话，Spring将调用Bean的setApplicationContext()方法，将bean所在应用上下文引用传入进来。
6、如果Bean实现了BeanPostProcessor接口，Spring就将调用他们的postProcessBeforeInitialization()方法。
7、如果Bean 实现了InitializingBean接口，Spring将调用他们的afterPropertiesSet()方法。类似的，如果bean使用init-method声明了初始化方法，该方法也会被调用
8、如果Bean 实现了BeanPostProcessor接口，Spring就将调用他们的postProcessAfterInitialization()方法。
9、此时，Bean已经准备就绪，可以被应用程序使用了。他们将一直驻留在应用上下文中，直到应用上下文被销毁。
10、如果bean实现了DisposableBean接口，Spring将调用它的destory()接口方法，同样，如果bean使用了destory-method 声明销毁方法，该方法也会被调用。
package com.example.springbean.component;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
@Component
public class MySpringBean implements BeanNameAware, BeanFactoryAware, ApplicationContextAware, InitializingBean, DisposableBean {
public MySpringBean() {
System.out.println("Bean通过构造方法进行实例化");
}
@Override
public void setBeanName(String name) {
System.out.println("Bean实现了BeanNameAware接口,执行setBeanName()方法,name = " + name);
}
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
System.out.println("Bean实现了BeanFactoryAware接口,执行setBeanFactory(),beanFactory=" + beanFactory.getClass().getCanonicalName());
}
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
System.out.println("Bean实现了ApplicationContextAware接口,调用setApplicationContext()方法，applicationContext=" + applicationContext.getDisplayName());
}
@Override
public void destroy() throws Exception {
System.out.println("Bean实现了DisposableBean接口,调用destroy()方法");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("Bean 实现了InitializingBean接口,调用afterPropertiesSet()方法");
}
}
package com.example.springbean.component;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
@Component
public class MySpringBeanProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof MySpringBean) {
System.out.println("Bean实现了BeanPostProcessor接口,调用postProcessBeforeInitialization()");
}
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof MySpringBean) {
System.out.println("Bean实现了BeanPostProcessor接口,postProcessAfterInitialization()");
}
return bean;
}
}
D:softwareJavajdk1.8.0_221binjava.exe -XX:TieredStopAtLevel=1 -noverify -Dspring.output.ansi.enabled=always "-javaagent:D:softwareIntelliJ IDEA 2021.2.3libidea_rt.jar=4880:D:softwareIntelliJ IDEA 2021.2.3bin" -Dcom.sun.management.jmxremote -Dspring.jmx.enabled=true -Dspring.liveBeansView.mbeanDomain -Dspring.application.admin.enabled=true -Dfile.encoding=UTF-8 -classpath D:softwareJavajdk1.8.0_221jrelibcharsets.jar;D:softwareJavajdk1.8.0_221jrelibdeploy.jar;D:softwareJavajdk1.8.0_221jrelibextaccess-bridge-64.jar;D:softwareJavajdk1.8.0_221jrelibextcldrdata.jar;D:softwareJavajdk1.8.0_221jrelibextdnsns.jar;D:softwareJavajdk1.8.0_221jrelibextjaccess.jar;D:softwareJavajdk1.8.0_221jrelibextjfxrt.jar;D:softwareJavajdk1.8.0_221jrelibextlocaledata.jar;D:softwareJavajdk1.8.0_221jrelibextnashorn.jar;D:softwareJavajdk1.8.0_221jrelibextsunec.jar;D:softwareJavajdk1.8.0_221jrelibextsunjce_provider.jar;D:softwareJavajdk1.8.0_221jrelibextsunmscapi.jar;D:softwareJavajdk1.8.0_221jrelibextsunpkcs11.jar;D:softwareJavajdk1.8.0_221jrelibextzipfs.jar;D:softwareJavajdk1.8.0_221jrelibjavaws.jar;D:softwareJavajdk1.8.0_221jrelibjce.jar;D:softwareJavajdk1.8.0_221jrelibjfr.jar;D:softwareJavajdk1.8.0_221jrelibjfxswt.jar;D:softwareJavajdk1.8.0_221jrelibjsse.jar;D:softwareJavajdk1.8.0_221jrelibmanagement-agent.jar;D:softwareJavajdk1.8.0_221jrelibplugin.jar;D:softwareJavajdk1.8.0_221jrelibresources.jar;D:softwareJavajdk1.8.0_221jrelibrt.jar;D:Workspacedemospring-beantargetclasses;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkbootspring-boot-starter2.6.7spring-boot-starter-2.6.7.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkbootspring-boot2.6.7spring-boot-2.6.7.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-context5.3.19spring-context-5.3.19.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkbootspring-boot-autoconfigure2.6.7spring-boot-autoconfigure-2.6.7.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkbootspring-boot-starter-logging2.6.7spring-boot-starter-logging-2.6.7.jar;D:softwareRepositoryMavenLocalRepositorychqoslogbacklogback-classic1.2.11logback-classic-1.2.11.jar;D:softwareRepositoryMavenLocalRepositorychqoslogbacklogback-core1.2.11logback-core-1.2.11.jar;D:softwareRepositoryMavenLocalRepositoryorgapachelogginglog4jlog4j-to-slf4j2.17.2log4j-to-slf4j-2.17.2.jar;D:softwareRepositoryMavenLocalRepositoryorgapachelogginglog4jlog4j-api2.17.2log4j-api-2.17.2.jar;D:softwareRepositoryMavenLocalRepositoryorgslf4jjul-to-slf4j1.7.36jul-to-slf4j-1.7.36.jar;D:softwareRepositoryMavenLocalRepositoryjakartaannotationjakarta.annotation-api1.3.5jakarta.annotation-api-1.3.5.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-core5.3.19spring-core-5.3.19.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-jcl5.3.19spring-jcl-5.3.19.jar;D:softwareRepositoryMavenLocalRepositoryorgyamlsnakeyaml1.29snakeyaml-1.29.jar;D:softwareRepositoryMavenLocalRepositoryorgslf4jslf4j-api1.7.36slf4j-api-1.7.36.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkbootspring-boot-starter-web2.6.7spring-boot-starter-web-2.6.7.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkbootspring-boot-starter-json2.6.7spring-boot-starter-json-2.6.7.jar;D:softwareRepositoryMavenLocalRepositorycomfasterxmljacksoncorejackson-databind2.13.2.1jackson-databind-2.13.2.1.jar;D:softwareRepositoryMavenLocalRepositorycomfasterxmljacksoncorejackson-annotations2.13.2jackson-annotations-2.13.2.jar;D:softwareRepositoryMavenLocalRepositorycomfasterxmljacksoncorejackson-core2.13.2jackson-core-2.13.2.jar;D:softwareRepositoryMavenLocalRepositorycomfasterxmljacksondatatypejackson-datatype-jdk82.13.2jackson-datatype-jdk8-2.13.2.jar;D:softwareRepositoryMavenLocalRepositorycomfasterxmljacksondatatypejackson-datatype-jsr3102.13.2jackson-datatype-jsr310-2.13.2.jar;D:softwareRepositoryMavenLocalRepositorycomfasterxmljacksonmodulejackson-module-parameter-names2.13.2jackson-module-parameter-names-2.13.2.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkbootspring-boot-starter-tomcat2.6.7spring-boot-starter-tomcat-2.6.7.jar;D:softwareRepositoryMavenLocalRepositoryorgapachetomcatembedtomcat-embed-core9.0.62tomcat-embed-core-9.0.62.jar;D:softwareRepositoryMavenLocalRepositoryorgapachetomcatembedtomcat-embed-el9.0.62tomcat-embed-el-9.0.62.jar;D:softwareRepositoryMavenLocalRepositoryorgapachetomcatembedtomcat-embed-websocket9.0.62tomcat-embed-websocket-9.0.62.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-web5.3.19spring-web-5.3.19.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-beans5.3.19spring-beans-5.3.19.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-webmvc5.3.19spring-webmvc-5.3.19.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-aop5.3.19spring-aop-5.3.19.jar;D:softwareRepositoryMavenLocalRepositoryorgspringframeworkspring-expression5.3.19spring-expression-5.3.19.jar com.example.springbean.SpringBeanApplication . ____ _ __ _ _ /\ / ___'_ __ _ _(_)_ __ __ _ ( ( )___ | '_ | '_| | '_ / _` | \/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |___, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.6.7) 2022-05-08 22:14:07.206 INFO 22504 --- [ main] c.e.springbean.SpringBeanApplication : Starting SpringBeanApplication using Java 1.8.0_221 on LAPTOP-CANO6289 with PID 22504 (D:Workspacedemospring-beantargetclasses started by Lenovo in D:Workspacedemospring-bean) 2022-05-08 22:14:07.208 INFO 22504 --- [ main] c.e.springbean.SpringBeanApplication : No active profile set, falling back to 1 default profile: "default" 2022-05-08 22:14:07.698 INFO 22504 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http) 2022-05-08 22:14:07.703 INFO 22504 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2022-05-08 22:14:07.703 INFO 22504 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.62] 2022-05-08 22:14:07.793 INFO 22504 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2022-05-08 22:14:07.793 INFO 22504 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 560 ms Bean通过构造方法进行实例化 Bean实现了BeanNameAware接口,执行setBeanName()方法,name = mySpringBean Bean实现了BeanFactoryAware接口,执行setBeanFactory(),beanFactory=org.springframework.beans.factory.support.DefaultListableBeanFactory Bean实现了ApplicationContextAware接口,调用setApplicationContext()方法，applicationContext=org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@4e08711f Bean实现了BeanPostProcessor接口,调用postProcessBeforeInitialization() Bean 实现了InitializingBean接口,调用afterPropertiesSet()方法 Bean实现了BeanPostProcessor接口,postProcessAfterInitialization() 2022-05-08 22:14:07.967 INFO 22504 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '' 2022-05-08 22:14:07.973 INFO 22504 --- [ main] c.e.springbean.SpringBeanApplication : Started SpringBeanApplication in 0.981 seconds (JVM running for 1.672) Bean实现了DisposableBean接口,调用destroy()方法 Process finished with exit code 130
