Spring Boot源码分析之外部tomcat启动war包的原理

前情提示:以前我们说过，springboot程序是jar的方式,是通过IOC容器启动带动了tomcat的启动
那么，我们把springboot的程序打成war的时候，是怎么样的原理了？(tomcat启动带动IOC容器的启动)
从疑问开始: 我们把springboot打成war的包时候，为什么要在启动类程序上实现 SpringBootServletInitializer 接口?
以及com.tuling.TulingvipSpringbootWarApplication#configure()是在什么时候触发调用的?

@SpringBootApplication
public class TulingvipSpringbootWarApplication extends SpringBootServletInitializer {
   
    public static void main(String[] args) {
   
        SpringApplication.run(TulingvipSpringbootWarApplication.class, args);
    }
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
    return application.sources(TulingvipSpringbootWarApplication.class);
    }
}

1 从servlet3.0的特性说起

8.2.4 Shared libraries / runtimes pluggability

The ServletContainerInitializer class is looked up via the jar services API. For each application, an instance of the ServletContainerInitializer is created by the container at application startup time. The framework providing an implementation of the ServletContainerInitializer MUST bundle in the META-INF/services directory of the jar file a file called javax.servlet.ServletContainerInitializer, as per the jar services API,that points to the implementation class of the ServletContainerInitializer. In addition to the ServletContainerInitializ