role of configuration classes in spring boot projects

Question

i am new to springboot application development and i generated my project with the help of this url https://start.spring.io/ and when i open this project in my IDE i had 2 classes generated this is the first class

    public class ServletInitializer extends SpringBootServletInitializer   {
    @Override
    protected SpringApplicationBuilder    configure(SpringApplicationBuilder application) {
        return application.sources(TravellingApplication.class);
    }}

and this is the second class

@SpringBootApplication
public class TravellingApplication {
public static void main(String[] args) {
    SpringApplication.run(TravellingApplication.class, args);
}}

i really don't get it whats happening inside the configure method in my Servletinitializer class. i can write better code configuration if i delete both of the classes and do something like this,

 class simmilar to dispatcherservlet.xml
 
 @Configuration
 @EnableWebMvc
 @ComponentScan(basePackages = "com.travelliing")
 public class WebConfig extends WebMvcConfigurerAdapter {
 }

  class simmilar to web.xml 

public class WebAppInitializer implements WebApplicationInitializer {
@Override
public void onStartup(ServletContext servletContext) throws    ServletException { } 
}
    

correct me if i am wrong. i think both ServletInitializer class and webAppInitializer is capable of same functionalities since the somehow implement WebApplicationInitializer. except for the configure method in servletInitializer class.

whats happening with the travellingApplication class annotated with @SpringBootApplication is it simmilar to my webConfig Class which extends WebMvcConfigureAdapter

Answer 1

Both classes load the Spring application context.

The class with the main method (TravellingApplication) will be used if you run your application as normal java application. For example if you do Run As -> Java applciatnion from Eclipse or if you package the application as a jar and run java -jar myApp.jar from the command line.

SpringBootServletInitializer will be used to load the application context if you package the application as a war file and deploy it in Tomcat or another web server that supports Servlet 3.0+. It basically replaces the web.xml.

i really don't get it whats happening inside the configure method in my Servletinitializer class.

TravellingApplication is a @Configuration class - it declares Spring beans and other Spring configuration, so this line - return application.sources(TravellingApplication.class); just loads this configuration (application context). The same thing that happens in the main method.

whats happening with the travellingApplication class annotated with @SpringBootApplication is it simmilar to my webConfig Class which extends WebMvcConfigureAdapter

@SpringBootApplication is just a shortcut to

 @Configuration
 @EnableAutoConfiguration
 @ComponentScan

See here.