Bean的生命周期

生命周期

一个受 Spring 管理的 bean，生命周期主要阶段有

创建：根据 bean 的构造方法或者工厂方法来创建 bean 实例对象

依赖注入：根据 @Autowired，@Value 或其它一些手段，为 bean 的成员变量填充值、建立关系

初始化：回调各种 Aware 接口，调用对象的各种初始化方法

销毁：在容器关闭时，会销毁所有单例对象（即调用它们的销毁方法）

prototype 对象也能够销毁，不过需要容器这边主动调用


@Component
public class LifeCycleBean {
    private static final Logger log = LoggerFactory.getLogger(LifeCycleBean.class);

    public LifeCycleBean() {
        log.debug("构造");
    }

    @Autowired
    public void autowire(@Value("${JAVA_HOME}") String home) {
        log.debug("依赖注入: {}", home);
    }

    @PostConstruct
    public void init() {
        log.debug("初始化");
    }

    @PreDestroy
    public void destroy() {
        log.debug("销毁");
    }
}


@SpringBootApplication
public class A03 {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(A03.class, args);
        context.close();
    }
}

Bean后置处理器增强

InstantiationAwareBeanPostProcessor和DestructionAwareBeanPostProcessor 分别对bean初始化和销毁之前增强

创建前的增强

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

postProcessBeforeDestruction

如 @PreDestroy

收获💡

Spring bean 生命周期各个阶段

模板设计模式, 指大流程已经固定好了, 通过接口回调（bean 后处理器）在一些关键点前后提供扩展




@Component
public class MyBeanPostProcessor implements InstantiationAwareBeanPostProcessor, DestructionAwareBeanPostProcessor {

    private static final Logger log = LoggerFactory.getLogger(MyBeanPostProcessor.class);

    @Override
    public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 销毁之前执行, 如 @PreDestroy");
    }

    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 实例化之前执行, 这里返回的对象会替换掉原本的 bean");
        return null;
    }

    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean")) {
            log.debug("<<<<<< 实例化之后执行, 这里如果返回 false 会跳过依赖注入阶段");
//            return false;
        }
        return true;
    }

    @Override
    public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 依赖注入阶段执行, 如 @Autowired、@Value、@Resource");
        return pvs;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 初始化之前执行, 这里返回的对象会替换掉原本的 bean, 如 @PostConstruct、@ConfigurationProperties");
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 初始化之后执行, 这里返回的对象会替换掉原本的 bean, 如代理增强");
        return bean;
    }
}


.   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.5.5)

[INFO ] 20:35:56.881 [main] com.onethink.a03.A03                - Starting A03 using Java 17.0.5 on OneThink with PID 7572 (E:\code\java\spring_learn\show\target\classes started by moonlight in E:\code\java\spring_learn\show) 
[DEBUG] 20:35:56.886 [main] com.onethink.a03.A03                - Running with Spring Boot v2.5.5, Spring v5.3.10 
[INFO ] 20:35:56.886 [main] com.onethink.a03.A03                - No active profile set, falling back to default profiles: default 
[WARN ] 20:35:57.271 [main] o.m.s.mapper.ClassPathMapperScanner - No MyBatis mapper was found in '[com.onethink.a03]' package. Please check your configuration. 
[TRACE] 20:35:57.363 [main] o.s.a.a.a.AnnotationAwareAspectJAutoProxyCreator - Did not attempt to auto-proxy infrastructure class [org.springframework.transaction.interceptor.BeanFactoryTransactionAttributeSourceAdvisor] 
[TRACE] 20:35:57.371 [main] o.s.a.a.a.AnnotationAwareAspectJAutoProxyCreator - Did not attempt to auto-proxy infrastructure class [org.springframework.transaction.interceptor.TransactionInterceptor] 
[INFO ] 20:35:57.525 [main] o.s.b.w.e.tomcat.TomcatWebServer    - Tomcat initialized with port(s): 8080 (http) 
[INFO ] 20:35:57.530 [main] o.a.coyote.http11.Http11NioProtocol - Initializing ProtocolHandler ["http-nio-8080"] 
[INFO ] 20:35:57.530 [main] o.a.catalina.core.StandardService   - Starting service [Tomcat] 
[INFO ] 20:35:57.530 [main] o.a.catalina.core.StandardEngine    - Starting Servlet engine: [Apache Tomcat/9.0.53] 
[INFO ] 20:35:57.587 [main] o.a.c.c.C.[Tomcat].[localhost].[/]  - Initializing Spring embedded WebApplicationContext 
[INFO ] 20:35:57.587 [main] o.s.b.w.s.c.ServletWebServerApplicationContext - Root WebApplicationContext: initialization completed in 674 ms 
[DEBUG] 20:35:57.614 [main] c.onethink.a03.MyBeanPostProcessor  - <<<<<< 实例化之前执行, 这里返回的对象会替换掉原本的 bean 
[DEBUG] 20:35:57.616 [main] com.onethink.a03.LifeCycleBean      - 构造 
[DEBUG] 20:35:57.617 [main] c.onethink.a03.MyBeanPostProcessor  - <<<<<< 实例化之后执行, 这里如果返回 false 会跳过依赖注入阶段 
[DEBUG] 20:35:57.617 [main] c.onethink.a03.MyBeanPostProcessor  - <<<<<< 依赖注入阶段执行, 如 @Autowired、@Value、@Resource 
[DEBUG] 20:35:57.618 [main] com.onethink.a03.LifeCycleBean      - 依赖注入: D:\DevEvn\jdk\jdk-17.0.5 
[DEBUG] 20:35:57.619 [main] c.onethink.a03.MyBeanPostProcessor  - <<<<<< 初始化之前执行, 这里返回的对象会替换掉原本的 bean, 如 @PostConstruct、@ConfigurationProperties 
[DEBUG] 20:35:57.619 [main] com.onethink.a03.LifeCycleBean      - 初始化 
[DEBUG] 20:35:57.619 [main] c.onethink.a03.MyBeanPostProcessor  - <<<<<< 初始化之后执行, 这里返回的对象会替换掉原本的 bean, 如代理增强 
[INFO ] 20:35:57.739 [main] o.s.b.a.w.s.WelcomePageHandlerMapping - Adding welcome page: class path resource [static/index.html] 
[INFO ] 20:35:57.798 [main] c.a.d.s.b.a.DruidDataSourceAutoConfigure - Init DruidDataSource 
[INFO ] 20:35:57.867 [main] c.a.druid.pool.DruidDataSource      - {dataSource-1} inited 
[INFO ] 20:35:58.004 [main] o.a.coyote.http11.Http11NioProtocol - Starting ProtocolHandler ["http-nio-8080"] 
[INFO ] 20:35:58.031 [main] o.a.c.c.C.[Tomcat].[localhost].[/]  - Initializing Spring DispatcherServlet 'dispatcherServlet' 
[INFO ] 20:35:58.031 [main] o.s.web.servlet.DispatcherServlet   - Initializing Servlet 'dispatcherServlet' 
[TRACE] 20:35:58.031 [main] o.s.web.servlet.DispatcherServlet   - Detected org.springframework.web.multipart.support.StandardServletMultipartResolver@9cfc77 
[TRACE] 20:35:58.031 [main] o.s.web.servlet.DispatcherServlet   - Detected org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver@7418d76e 
[TRACE] 20:35:58.031 [main] o.s.web.servlet.DispatcherServlet   - Detected org.springframework.web.servlet.theme.FixedThemeResolver@601eb4af 
[TRACE] 20:35:58.032 [main] o.s.web.servlet.DispatcherServlet   - Detected DefaultRequestToViewNameTranslator 
[TRACE] 20:35:58.032 [main] o.s.web.servlet.DispatcherServlet   - Detected SessionFlashMapManager 
[DEBUG] 20:35:58.032 [main] o.s.web.servlet.DispatcherServlet   - enableLoggingRequestDetails='false': request parameters and headers will be masked to prevent unsafe logging of potentially sensitive data 
[INFO ] 20:35:58.032 [main] o.s.web.servlet.DispatcherServlet   - Completed initialization in 1 ms 
[INFO ] 20:35:58.032 [main] o.s.b.w.e.tomcat.TomcatWebServer    - Tomcat started on port(s): 8080 (http) with context path '' 
[INFO ] 20:35:58.038 [main] com.onethink.a03.A03                - Started A03 in 1.383 seconds (JVM running for 1.835) 
[INFO ] 20:35:58.069 [main] c.a.druid.pool.DruidDataSource      - {dataSource-1} closing ... 
[INFO ] 20:35:58.070 [main] c.a.druid.pool.DruidDataSource      - {dataSource-1} closed 
[DEBUG] 20:35:58.071 [main] c.onethink.a03.MyBeanPostProcessor  - <<<<<< 销毁之前执行, 如 @PreDestroy 
[DEBUG] 20:35:58.071 [main] com.onethink.a03.LifeCycleBean      - 销毁 
Disconnected from the target VM, address: '127.0.0.1:57246', transport: 'socket'

bean后处理器的模板方法

spring 的bean后置处理器，通过模板方法的模式去增强


public class TestMethodTemplate {

    public static void main(String[] args) {
        MyBeanFactory beanFactory = new MyBeanFactory();
        beanFactory.addBeanPostProcessor(bean -> System.out.println("解析 @Autowired"));
        beanFactory.addBeanPostProcessor(bean -> System.out.println("解析 @Resource"));
        beanFactory.getBean();
    }

    // 模板方法  Template Method Pattern
    static class MyBeanFactory {
        public Object getBean() {
            Object bean = new Object();
            System.out.println("构造 " + bean);
            System.out.println("依赖注入 " + bean); // @Autowired, @Resource
            for (BeanPostProcessor processor : processors) {
                processor.inject(bean);
            }
            System.out.println("初始化 " + bean);
            return bean;
        }

        private List<BeanPostProcessor> processors = new ArrayList<>();

        public void addBeanPostProcessor(BeanPostProcessor processor) {
            processors.add(processor);
        }
    }

    static interface BeanPostProcessor {
        public void inject(Object bean); // 对依赖注入阶段的扩展
    }
}