SpringBoot专栏：巧妙运用SpringBoot的事件监听机制，原来这么重要..

你的名字 2022-04-10 05:56 419阅读 0赞

## ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p6aHVhbl8x_size_16_color_FFFFFF_t_70][] ##

## 前言 ##

SpringBoot涉及了几个比较重要的事件回调机制，巧妙运用给开发者带来不一样的”福利“。

回调：**ApplicationContextInitializer、SpringApplicationRunListener、CommandLineRunner、ApplicationRunner**

在SpringBoot启动的时候，以上几个回调事件是何时触发的？下面样例中会有详细讲解。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p6aHVhbl8x_size_16_color_FFFFFF_t_70 1][]

## 哪些场景会用到 ##

1.启动前环境检测？

2.启动时配置初始化？

3.启动后数据初始化？

...

应用的场景很多，可以发挥我们的想象。

## 事件回调机制 ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p6aHVhbl8x_size_16_color_FFFFFF_t_70 2][]

## 代码样例 ##

分别对4个类继承

HelloApplicationContextInitializer

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p6aHVhbl8x_size_16_color_FFFFFF_t_70 3][]

HelloApplicationRunner

@Component
    public class HelloApplicationRunner implements ApplicationRunner {
        @Override
        public void run(ApplicationArguments args) throws Exception {
            System.out.println("运行ApplicationRunner:ApplicationRunner...run....");
        }
    }

HelloCommandLineRunner类

@Component
    public class HelloCommandLineRunner implements CommandLineRunner {
        @Override
        public void run(String... args) throws Exception {
            System.out.println("运行LineRunner：CommandLineRunner...run..."+ Arrays.asList(args));
        }
    }

HelloSpringApplicationRunListener类

package com.limp.listerner;
    
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.SpringApplicationRunListener;
    import org.springframework.context.ConfigurableApplicationContext;
    import org.springframework.core.env.ConfigurableEnvironment;
    
    public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
    
        //必须有的构造器
        public HelloSpringApplicationRunListener(SpringApplication application, String[] args){
    
        }
    
        @Override
        public void starting() {
            System.out.println("运行RunListener：SpringApplicationRunListener...starting...");
        }
    
        @Override
        public void environmentPrepared(ConfigurableEnvironment environment) {
            Object o = environment.getSystemProperties().get("os.name");
            System.out.println("获取系统环境：SpringApplicationRunListener...environmentPrepared.."+o);
        }
    
        @Override
        public void contextPrepared(ConfigurableApplicationContext context) {
            System.out.println("SpringApplicationRunListener...contextPrepared...");
        }
    
        @Override
        public void contextLoaded(ConfigurableApplicationContext context) {
            System.out.println("SpringApplicationRunListener...contextLoaded...");
        }
    
        @Override
        public void started(ConfigurableApplicationContext context) {
    
        }
    
        @Override
        public void running(ConfigurableApplicationContext context) {
    
        }
    
        @Override
        public void failed(ConfigurableApplicationContext context, Throwable exception) {
    
        }
    
    
    }

注意上面2个类需要META-INF/spring.factories添加如下配置才能生效

org.springframework.context.ApplicationContextInitializer=\
    com.limp.listerner.HelloApplicationContextInitializer
    
    org.springframework.boot.SpringApplicationRunListener=\
    com.limp.listerner.HelloSpringApplicationRunListener

## 开始测试 ##

启动应用...运行结果如下

运行RunListener：SpringApplicationRunListener...starting...
    获取系统环境：SpringApplicationRunListener...environmentPrepared..Windows 10
    .....
    运行Initializer:ApplicationContextInitializer...initialize...org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@557cd14f: startup date [Thu Jan 01 08:00:00 CST 1970]; root of context hierarchy
    
    运行ApplicationRunner:ApplicationRunner...run....
    运行LineRunner：CommandLineRunner...run...[]

源码地址：

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