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SpringBoot版本：2.1.1.RELEASE

在SpringApplication对象创建和run()方法的运行过程中，我们可以发现有几个重要的事件回调机制，分别是：

1. ApplicationContextInitializer
2. SpringApplicationRunListener
3. ApplicationRunner
4. CommandLineRunner

这几个重要的事件回调机制在很多环境下都有应用，例如：

1. 启动前的环境检测
2. 启动时的配置初始化
3. 启动后的数据初始化

下面将会对这四个事件回调机制进行详细的讲解：

1. ApplicationContextInitializer

   首先SpringBoot项目启动时，会先创建SpringApplication对象，在创建对象过程中，会将根路径下的META-INF/spring.factories 文件中的 key为org.springframework.context.ApplicationContextInitializer的值加入SpringApplication对象的属性 List<ApplicationContextInitializer<?>> initializers中
   
   SpringApplication对象创建完成，会运行run方法，然后在容器初始化的时候调用applyInitializers(context)方法实例化initializers属性中保存的值。如下图：
   
   

   2.SpringApplicationRunListener

   SpringBoot启动过程中多次被回调，详细可参考：

   3.ApplicationRunner、CommandLineRunner

   容器启动完成之后回调，其中ApplicationRunner比CommandLineRunner先执行，一般可用于系统数据的初始化
   

代码示例：

1.代码结构

2.代码工程

package com.van.springbootdemo7.listeners;import org.springframework.context.ApplicationContextInitializer;import org.springframework.context.ConfigurableApplicationContext;/** * description: * * @author van.shu * @date 2019/5/28 23:03 */public class MyApplicaitonInitilizer implements ApplicationContextInitializer
   
     {
       @Override    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
           System.out.println("MyApplicaitonInitilizer...running...");    }}
   

package com.van.springbootdemo7.listeners;import org.springframework.boot.ApplicationArguments;import org.springframework.boot.ApplicationRunner;import org.springframework.stereotype.Component;/** * description: * * @author van.shu * @date 2019/5/28 23:09 */@Componentpublic class MyApplicaitonRunner implements ApplicationRunner {
       @Override    public void run(ApplicationArguments args) throws Exception {
           System.out.println("MyApplicaitonRunner...running...");    }}

然后将上面两个类的路径加入到资源路径下META-INF/spring.factories配置文件中

org.springframework.context.ApplicationContextInitializer=\  com.van.springbootdemo7.listeners.MyApplicaitonInitilizerorg.springframework.boot.SpringApplicationRunListener=\  com.van.springbootdemo7.listeners.MyApplicationRunLIstener

最后再实现另外两个事件回调接口ApplicaitonRunner和CommandLineRunner:

package com.van.springbootdemo7.listeners;import org.springframework.boot.SpringApplication;import org.springframework.boot.SpringApplicationRunListener;import org.springframework.context.ConfigurableApplicationContext;import org.springframework.core.env.ConfigurableEnvironment;/** * description: * * @author van.shu * @date 2019/5/28 23:06 */public class MyApplicationRunLIstener implements SpringApplicationRunListener {
       public MyApplicationRunLIstener(SpringApplication application, String[] args) {
       }    @Override    public void starting() {
           System.out.println("MyApplicationRunLIstener...starting...");    }    @Override    public void environmentPrepared(ConfigurableEnvironment environment) {
       }    @Override    public void contextPrepared(ConfigurableApplicationContext context) {
       }    @Override    public void contextLoaded(ConfigurableApplicationContext context) {
       }    @Override    public void started(ConfigurableApplicationContext context) {
       }    @Override    public void running(ConfigurableApplicationContext context) {
       }    @Override    public void failed(ConfigurableApplicationContext context, Throwable exception) {
       }}

package com.van.springbootdemo7.listeners;import org.springframework.boot.CommandLineRunner;import org.springframework.stereotype.Component;/** * description: * * @author van.shu * @date 2019/5/28 23:10 */@Componentpublic class MyCommandLineRunner implements CommandLineRunner {
       @Override    public void run(String... args) throws Exception {
           System.out.println("MyCommandLineRunner...running...");    }}

运行效果如下：

Connected to the target VM, address: '127.0.0.1:10623', transport: 'socket'MyApplicationRunLIstener...starting...  .   ____          _            __ _ _ /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/  ___)| |_)| | | | | || (_| |  ) ) ) )  '  |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot ::        (v2.1.1.RELEASE)MyApplicaitonInitilizer...running.........(启动信息省略)2019-06-05 00:57:37.393  INFO 9992 --- [           main] c.v.s.SpringbootDemoApplication          : Started SpringbootDemoApplication in 5.989 seconds (JVM running for 6.406)MyApplicaitonRunner...running...MyCommandLineRunner...running...

总结：

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