本文来聊一下在spring中，当spring 容器启动后，我们有几种初始化操作的方式。

在spring 容器中有一个 Persion对象名字叫张三，需要在spring容器启动后调用它的run方法。代码如下

---

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

@Configuration
public class PersonConfig {

    @Bean
    public Person person(){
        Person person = new Person();
        person.setName("张三");
        person.setAge(18);
        return person;
    }
}

---

一、ContextRefreshedEvent事件

ContextRefreshedEvent：是Spring容器初始化完成后调用的事件。
ContextRefreshedEvent的父类是ApplicationContextEvent，是一个事件。所以我们通过ApplicationListener来实现。

代码如下：

import com.example.springbootdemo.bean.Person;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;

@Component
public class PersonAfterListener implements ApplicationListener<ContextRefreshedEvent> {
    @Autowired
    private Person person;

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        person.run("ContextRefreshedEvent");
    }
}

输出结果：

二、PostConstruct 注解

PostConstruct注解修饰的方式，是在spring容器启动时运行的。优先级大于ContextRefreshedEvent事件。

代码如下：

import com.example.springbootdemo.bean.Person;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

@Component
public class PersonAfterPostConstruct {
    @Autowired
    private Person person;

    @PostConstruct
    public void postConstruct(){
        person.run("PostConstruct");
    }
}

输出结果：

由此可见，PostConstruct优先级大于ContextRefreshedEvent事件。

三、InitializingBean

InitializingBean是spring容器在启动并初始化好内部示例后调用的，用来最终为总体bean添加最后属性和操作。

官方原话：This method allows the bean instance to perform validation of its overall configuration and final initialization when all bean properties have been set.

代码如下：

import com.example.springbootdemo.bean.Person;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class PersonAfterInitializingBean implements InitializingBean {
    @Autowired
    private Person person;

    @Override
    public void afterPropertiesSet() throws Exception {
        person.run("InitializingBean");
    }
}

输出结果：

四、init-method方法

这种方法有一定的局限性，并且可能会覆盖曾经的init操作，需要慎用。

Bean在加载到Spring容器中时需要先将Bean的定义信息抽象为BeanDefinition，其中有一个属性init-method代表将来Bean初始化时要调用的方法。

我们通过BeanFactoryPostProcessor来注入init-method方法，并且该方法必须是没有参数的。

代码如下：

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;

@Component
public class PersonAfterInit implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        BeanDefinition person = beanFactory.getBeanDefinition("person");
        person.setInitMethodName("run");
    }
}

输出结果：

五 、实现 SmartInitializingSingleton 接口

SmartInitializingSingleton是Bean容器在初始化所有非懒加载的单例Bean后调用的方法。

代码如下：

import com.example.springbootdemo.bean.Person;
import org.springframework.beans.factory.SmartInitializingSingleton;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class PersonAfterSmartInitializingSingleton implements SmartInitializingSingleton {
    @Autowired
    private Person person;

    @Override
    public void afterSingletonsInstantiated() {
        person.run("SmartInitializingSingleton");
    }
}

输出结果：

六、重写 onRefresh()方法

这个我实在是不会，但我不藏着掖着，告诉你也能实现。

七、CommandLineRunner（仅限Spring Boot）

CommandLineRunner 是一个Spring boot 接口，在应用初始化后执行，且仅会执行一次。可以用来打印项目中配置文件的参数，方便排查问题。

代码如下：

import com.example.springbootdemo.bean.Person;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class PersonAfterCommandLineRunner implements CommandLineRunner {
    @Autowired
    private Person person;

    @Override
    public void run(String... args) throws Exception {
        person.run("CommandLineRunner");
    }
}

输出结果：

八、SpringApplicationRunListener（仅限Spring boot）

SpringBoot的生命周期事件监听方法，需要搭配resource/META-INF/spring.factories 文件使用。

代码如下：

JAVA代码：

import com.example.springbootdemo.bean.Person;
import org.springframework.boot.ConfigurableBootstrapContext;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;

import java.time.Duration;


public class PersonAfterSpringApplicationRunListener implements SpringApplicationRunListener {
    private final SpringApplication application;
    private final String[] args;

    public PersonAfterSpringApplicationRunListener(SpringApplication application, String[] args) {
        this.application = application;
        this.args = args;
    }

    @Override
    public void starting(ConfigurableBootstrapContext bootstrapContext) {
        /*
         * Person has not been registered
         */
//        Person person = bootstrapContext.get(Person.class);
//        person.run("SpringApplicationRunListener:starting");
    }

    @Override
    public void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) {
        /*
         * Person has not been registered
         */
//        Person person = bootstrapContext.get(Person.class);
//        person.run("SpringApplicationRunListener:environmentPrepared");
    }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        /*
         * Person has not been registered
         */
//        Person person = context.getBean(Person.class);
//        person.run("SpringApplicationRunListener:contextPrepared");
    }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        /*
         * Person has not been registered
         */
//        Person person = context.getBean(Person.class);
//        person.run("SpringApplicationRunListener:contextLoaded");
    }

    @Override
    public void started(ConfigurableApplicationContext context, Duration timeTaken) {
        Person person = context.getBean(Person.class);
        person.run("SpringApplicationRunListener:started");
    }

    @Override
    public void ready(ConfigurableApplicationContext context, Duration timeTaken) {
        Person person = context.getBean(Person.class);
        person.run("SpringApplicationRunListener:ready");
    }

    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) {
        Person person = context.getBean(Person.class);
        person.run("SpringApplicationRunListener:failed");
    }
}

spring.factories

org.springframework.boot.SpringApplicationRunListener=com.example.springbootdemo.impl.PersonAfterSpringApplicationRunListener

输出结果：

总结：

执行优先级：init-Method >> InitializingBean >> PostConstruct >> SmartInitializingSingleton >> ContextRefreshedEvent >> SpringApplicationRunListener:started >> CommandLineRunner >> SpringApplicationRunListener:ready