spring探秘:通过BeanPostProcessor、@PostConstruct、InitializingBean在启动前执行方法

springboot启动前执行方法的3种方式：实现BeanPostProcessor接口、实现InitializingBean接口、使用@PostConstruct注解

示例：

第一种 实现BeanPostProcessor接口

@Configuration
public class Test3 implements BeanPostProcessor {

    @Autowired
    private Environment environment;
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        String property = environment.getProperty("aaa.bbb");
        System.out.println("test3"+property);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

第二种 实现InitializingBean接口

@Configuration
public class Test2 implements InitializingBean {

    @Autowired
    private Environment environment;

    @Override
    public void afterPropertiesSet() throws Exception {
        String property = environment.getProperty("aaa.bbb");
        System.out.println("test2"+property);
    }

}

第三种 使用@PostConstruct注解

@Configuration
public class Test1 {

    @Autowired
    private Environment environment;

    @PostConstruct
    public void test(){
        String property = environment.getProperty("aaa.bbb");
        System.out.println("test1"+property);
    }

}

运行的优先级是：

启动类前->BeanPostProcessor->@PostConstruct->InitializingBean

需注意：BeanPostProcessor的方式会让实现类里的方法提前执行。BeanPostProcessor为每一个spring维护的对象调用前后做操作，实现了它我们当前类就会变成一个BeanPostProcessor对象，就可以像BeanPostProcessor一样在容器加载最初的几个阶段被实例化，只要被实例化，PostConstruct注解的标注的方法就会立即执行。

参考：https://www.jianshu.com/p/1845fe64decd
https://www.jianshu.com/p/1417eefd2ab1

原文地址：https://www.cnblogs.com/feng-gamer/p/12001205.html