@Configuration
public class Test1 {
    @Autowired
    private Environment environment;
    @PostConstruct
    public void test(){
        String property = environment.getProperty("aaa.bbb");
        System.out.println("test1"+property);
    }
}

第二種實現(xiàn)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);
    }
}

第三種實現(xiàn)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;
    }
}

第四種在啟動類run之前執(zhí)行方法

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        System.out.println("test4");
        SpringApplication.run(DemoApplication.class, args);
    }
}

當(dāng)然這是不可取的

他們運行的優(yōu)先級是

啟動類前->BeanPostProcessor->@PostConstruct->InitializingBean

值得注意的是第三種方式，他可以讓實現(xiàn)類里的方法提前執(zhí)行

同樣的使用@PostConstruct的兩個類

@Configuration
public class Test1 {
    @PostConstruct
    public void test(){
        System.out.println("test1");
    }
}

第一個沒有實現(xiàn)BeanPostProcessor接口

@Configuration
public class Test3 implements BeanPostProcessor {
    @Autowired
    private Environment environment;
    @PostConstruct
    public void  test(){
        System.out.println("test3");
    }
}

第二個實現(xiàn)了BeanPostProcessor接口，但是沒有重寫他的方法

打印結(jié)果如下