SpringBoot原理发现（四）

说明：

本系列基于SpringBoot 2.2.9.RELEASE 版本，对SpringBoot的原理进行分析，一共分为四节：

SpringBoot原理发现（一）：创建Hello World，对pom依赖以及@SpringBootApplication注解进行分析

SpringBoot原理发现（二）：分析SpringBoot自动配置原理

SpringBoot原理发现（三）：通过主配置类main方法分析SpringBoot启动配置原理

SpringBoot原理发现（四）：了解SpringBoot启动中的几个重要回调机制
 

SpringBoot回调机制

  针对SpringBoot原理发现（三）第二步骤springApplication.run(args)应用启动中包含的回调机制，编写如下四个实现类，主要观察启动流程

 

 1.ApplicationContextInitializer

@Component
public class MyApplicationContextInitializer implements ApplicationContextInitializer {

    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        System.out.println("MyApplicationContextInitializer initialize ...");
    }
}

 2.SpringApplicationRunListener

@Component
public class MySpringApplicationRunListener implements SpringApplicationRunListener {

    public MySpringApplicationRunListener(){}
    public MySpringApplicationRunListener(SpringApplication application, String[] args){}

    public void starting() {
        System.out.println("MySpringApplicationRunListener starting...");
    }


    public void environmentPrepared(ConfigurableEnvironment environment) {
        System.out.println("MySpringApplicationRunListener environmentPrepared...");
    }


    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("MySpringApplicationRunListener contextPrepared...");
    }


    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("MySpringApplicationRunListener contextLoaded...");
    }

    public void started(ConfigurableApplicationContext context) {
        System.out.println("MySpringApplicationRunListener started...");
    }


    public void running(ConfigurableApplicationContext context) {
        System.out.println("MySpringApplicationRunListener running...");
    }

}

　通过SpringBoot原理发现（三）知道ApplicationContextInitializer和SpringApplicationRunListener是从
　META-INF/spring.factories读取的，所以需要配置该文件。

META-INF/spring.factories配置：

# Initializers
org.springframework.context.ApplicationContextInitializer=\
com.example.demo.listener.MyApplicationContextInitializer

org.springframework.boot.SpringApplicationRunListener=\
com.example.demo.listener.MySpringApplicationRunListener

 3.ApplicationRunner

@Component
public class MyApplicationRunner implements ApplicationRunner {

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("MyApplicationRunner run...");

    }
}

4.CommandLineRunner

@Component
public class MyCommandLineRunner implements CommandLineRunner {

    @Override
    public void run(String... args) throws Exception {
        System.out.println("MyCommandLineRunner run");
    }
}

输出

观察结果能验证出输出顺序和上一篇文章分析结果一样

MySpringApplicationRunListener starting...
MySpringApplicationRunListener environmentPrepared...

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.2.9.RELEASE)

MyApplicationContextInitializer initialize ...
MySpringApplicationRunListener contextPrepared...
2020-10-30 17:46:09.280  INFO 5132 --- [           main] com.example.demo.DemoApplication         : Starting DemoApplication on 
2020-10-30 17:46:09.283  INFO 5132 --- [           main] com.example.demo.DemoApplication         : No active profile set, falling back to default profiles: default
MySpringApplicationRunListener contextLoaded...
2020-10-30 17:46:10.410  INFO 5132 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-10-30 17:46:10.425  INFO 5132 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-10-30 17:46:10.426  INFO 5132 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.37]
2020-10-30 17:46:10.574  INFO 5132 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-10-30 17:46:10.579  INFO 5132 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1256 ms
2020-10-30 17:46:10.766  INFO 5132 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2020-10-30 17:46:10.966  INFO 5132 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-10-30 17:46:10.970  INFO 5132 --- [           main] com.example.demo.DemoApplication         : Started DemoApplication in 3.292 seconds (JVM running for 3.959)
MySpringApplicationRunListener started...
MyApplicationRunner run...
MyCommandLineRunner run
MySpringApplicationRunListener running...