SpringBoot启动时初始化资源的几种方法

SpringBoot提供了多种方法可实现在启动过程中初始化资源

1. 使用注解@PostConstruct
2. 实现InitializingBean接口
3. 实现CommandLineRunner接口
4. 实现ApplicationRunner接口
5. 监听Spring事件ContextRefreshedEvent

以上5个方法的执行顺序为：

Bean初始化-》依赖注入-》@PostConstruct-》InitializingBean接口-》ContextRefreshedEvent-》ApplicationRunner接口-》CommandLineRunner接口

Talk is cheap. Show me the code!

以下代码在同一个Bean实现以上多种初始化方法，并在每个阶段打印日志信息。

package com.makai.initorder;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.CommandLineRunner;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;

import javax.annotation.PostConstruct;

/**
 * @ClassName InitClass
 * @Description TODO
 * @Author m00381966
 * @Date 2019/9/2 19:42
 * @Version 1.0
 */
public class InitClass implements InitializingBean, CommandLineRunner, ApplicationRunner, ApplicationListener {

    public InitClass() {
        System.out.println("now is doing construct method");
    }

    //bean初始化后执行
    @PostConstruct
    public void postConstruct() {
        System.out.println("now is doing @PostConstruct");
    }

    //bean指定initMethod方法，bean初始化后执行
    public void initMethod() {
        System.out.println("now is doing initMethod");
    }

    //实现ApplicationRunner，bean初始化后执行
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("now is doing afterPropertiesSet");
    }

    //实现CommandLineRunner，SpringBoot启动后后执行
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("now is doing run method of ApplicationRunner Interface");
    }

    //实现CommandLineRunner，SpringBoot启动后后执行
    @Override
    public void run(String... args) throws Exception {
        System.out.println("now is doing run method of CommandLineRunner Interface");
    }

    //监听SpringBean加载事件，在springboot 初始化完成时执行
    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        System.out.println("now is doing something when catch a contextRefreshedEvent");
    }
}

package com.makai.demo;

import com.makai.initorder.InitClass;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
@ComponentScan({"com.makai"})
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);

    }

    @Bean(initMethod = "initMethod")
    public InitClass initClass(){
        return new InitClass();
    }
}

启动过程中打印如下，可以验证各个接口的执行顺序。实际应用中按需选择。