这里介绍在SpringBoot Bean生命周期当中常用的Hook

Bean实例化时的Hook

Spring Boot Bean在实例化时常用的Hook有：

@PostConstruct注解
InitializingBean接口的afterPropertiesSet方法
@Bean注解的initMethod属性

调用顺序依次为：@PostConstruct注解标记的方法 -> InitializingBean接口的afterPropertiesSet方法 -> @Bean注解中initMethod属性指定的方法

import org.springframework.beans.factory.InitializingBean;
import javax.annotation.PostConstruct;
import lombok.extern.slf4j.Slf4j;

@Slf4j
public class Dog implements InitializingBean {
    public void hello() {
        log.info("call by hook: @PostConstruct");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        log.info("call by hook: afterPropertiesSet of InitializingBean");
    }

    public void hi() {
        log.info("call by hook: initMethod of @Bean");
    }
}

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class DogConfig {

    @Bean(initMethod = "hi")
    public Dog dog() {
        return new Dog();
    }
}

特别地，BeanPostProcessor接口则可用于拦截所有Bean的实例化。具体地：

postProcessBeforeInitialization方法：该方法会在调用Bean的初始化方法之前被调用
postProcessAfterInitialization方法：该方法会在调用Bean的初始化方法之后被调用

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

@Component
@Slf4j
public class MyCustomBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        log.info("exec before method, bean name: {}", beanName);
        return BeanPostProcessor.super.postProcessBeforeInitialization(bean, beanName);
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        log.info("exec after method, bean name {}", beanName);
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
}

Bean销毁时的Hook

Spring Boot Bean在销毁时常用的Hook有：

@PreDestroy注解
DisposableBean接口的destroy方法
@Bean注解的destroyMethod属性

调用顺序依次为：@PreDestroy注解注解标记的方法 -> DisposableBean接口的destroy方法 -> @Bean注解中destroyMethod属性指定的方法

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.DisposableBean;
import javax.annotation.PreDestroy;

@Slf4j
public class Male implements DisposableBean {

    @PreDestroy
    public void gg() {
        log.info("call by hook: @PreDestroy");
    }

    @Override
    public void destroy() throws Exception {
        log.info("call by hook: destroy of DisposableBean");
    }

    public void bye() {
        log.info("call by hook: destroyMethod of @Bean");
    }

}

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MaleConfig {

    @Bean(destroyMethod = "bye")
    public Male male() {
        return new Male();
    }

}

Note: 利用@Bean注解创建实例时需要注意，@Bean注解存在 销毁方法推断 的行为。即如果没有显式设置destroyMethod属性时，其会将public公共的、无参的、命名为close或shutdown的方法自动注册为该Bean的销毁方法。如果需要禁用某个@Bean注解的 销毁方法推断 行为，可以将destroyMethod属性显式设置为””空字符串

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SpringBoot Bean生命周期的Hook

Bean实例化时的Hook

Bean销毁时的Hook