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 .