init-method，@postcontruct,afterPropertiesSet的先后顺序；

系统管理员 2022-10-06 15:52 155阅读 0赞

在牛客面经上遇到的一个面试题。突然想尝试下 然后就开始做了

## 测试 ##

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
            TestDao testDao = applicationContext.getBean(TestDao.class);
            ((ClassPathXmlApplicationContext) applicationContext).close();

测试的bean

@Component
    public class TestDao  implements InitializingBean, DisposableBean {
        public TestDao() {
            System.out.println("constructor");
        }
    
        @Async
        public void query(){
            System.out.println("Hello Spring!");
        }
    
        @Override
        public void afterPropertiesSet() throws Exception {
            System.out.println("afterPropertiesSet");
        }
        @PostConstruct
        public void PostConstruct(){
            System.out.println("PostConstruct");
        }
    
        public void InitMethod(){
            System.out.println("InitMethod");
        }
    
        @Override
        public void destroy() throws Exception {
            System.out.println("destroy");
        }
        @PreDestroy
        public void PreDestroy(){
            System.out.println("PreDestroy");
        }
        public void destroyMethod(){
            System.out.println("destroyMethod");
        }
    }

xml

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:tx="http://www.springframework.org/schema/tx"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:context="http://www.springframework.org/schema/context"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            https://www.springframework.org/schema/beans/spring-beans.xsd
    
            http://www.springframework.org/schema/tx
            https://www.springframework.org/schema/tx/spring-tx.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
    
        <context:annotation-config/>
        <bean id="testDao" class="com.test.dao.TestDao" init-method="InitMethod" destroy-method="destroyMethod"></bean>
    
    </beans>

执行之后打印的结果 ![file][] 总的来说就是打印的结果是构造方法->注解@PostConstruct方法->InitializingBean接口的afterPropertiesSet方法->xml中配置的init-method方法 同理销毁也是一样注解@PreDestroy方法->DisposableBean接口的destroy方法->xml中配置的destroy-method方法

## 源码 ##

通过断点调试发现几个初始化方法都定位到了AbstractAutowireCapableBeanFactory的initializeBean方法中

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                    invokeAwareMethods(beanName, bean);
                    return null;
                }, getAccessControlContext());
            }
            else {
                invokeAwareMethods(beanName, bean);
            }
    
            Object wrappedBean = bean;
            if (mbd == null || !mbd.isSynthetic()) {
            //此处执行的是@PostConstruct注解的方法 InitDestroyAnnotationBeanPostProcessor#postProcessBeforeInitialization
                wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
            }
    
            try {
            //执行的是afterPropertiesSet和init-method方法
                invokeInitMethods(beanName, wrappedBean, mbd);
            }
            catch (Throwable ex) {
                throw new BeanCreationException(
                        (mbd != null ? mbd.getResourceDescription() : null),
                        beanName, "Invocation of init method failed", ex);
            }
            if (mbd == null || !mbd.isSynthetic()) {
                wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
            }
    
            return wrappedBean;
        }

后面执行的两个方法 protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd) throws Throwable \{

boolean isInitializingBean = (bean instanceof InitializingBean);
        if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
            if (logger.isTraceEnabled()) {
                logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
            }
            if (System.getSecurityManager() != null) {
                try {
                    AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
                        ((InitializingBean) bean).afterPropertiesSet();
                        return null;
                    }, getAccessControlContext());
                }
                catch (PrivilegedActionException pae) {
                    throw pae.getException();
                }
            }
            else {
            //执行afterPropertiesSet方法
                ((InitializingBean) bean).afterPropertiesSet();
            }
        }
    
        if (mbd != null && bean.getClass() != NullBean.class) {
            String initMethodName = mbd.getInitMethodName();
            if (StringUtils.hasLength(initMethodName) &&
                    !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
                    !mbd.isExternallyManagedInitMethod(initMethodName)) {
                    //执行的是xml中自定义的init-method方法
                invokeCustomInitMethod(beanName, bean, mbd);
            }
        }
    }

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![file][file 1]

[file]: /images/20221005/a948206b21ec4fcc98387eab116057ba.png
[https_github.com_zhendiao_JavaInterview]: https://github.com/zhendiao/JavaInterview
[file 1]: /images/20221005/7f66d5cf0a8c4a598440069dffc9bb0e.png