spring boot war package starts principles

spring boot war started is the use of Servlet 3.0 new ServletContainerInitializer interface implementation.

 

Main logic

1. Spring in the spring-web-version.jar / META-INF / services / javax.servlet.ServletContainerInitializer document, disposed on a spring org.springframework.web.SpringServletContainerInitializer ServletContainerInitializer implementation class interface.
2. Servlet Container scanning start phase jar package META-INF / services / javax.servlet.ServletContainerInitializer file, obtaining ServletContainerInitializer implementation class and instantiated, the analytic ServletContainerInitializer @HandlesTypes annotation, to find out the type of collection @HandlesTypes defined as ServletContainerInitializer. OnStartup Method the first process parameter c.
3. Servlet Container in turn calls onStartup each ServletContainerInitializer instance. Scene war package calls initiated in SpringServletContainerInitializer.onStartup, the method set for each cycle is called c WebApplicationInitializer subclass (i.e. SpringBootServletInitializer) of onStartup method.
4. SpringBootServletInitializer.onStartup method calls SpringBootServletInitializer.createRootApplicationContext method, createRootApplicationContext method SpringApplication build and execute the entire spring SpringApplication.run method to initiate the project.

Source

Spring's implementation class ServletContainerInitializer

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
......
     @Override
     public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
              throws ServletException {
          List<WebApplicationInitializer> initializers = new LinkedList<>();
          if (webAppInitializerClasses != null) {
              for (Class<?> waiClass : webAppInitializerClasses) {
                   // Be defensive: Some servlet containers provide us with invalid classes,
                   // no matter what @HandlesTypes says...
                   if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
                             WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
                        try {
                             initializers.add((WebApplicationInitializer)ReflectionUtils.accessibleConstructor(waiClass).newInstance());
                        } catch (Throwable ex) {
                             throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
                        }
                   }
              }
          }
          if (initializers.isEmpty()) {
              servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
              return;
          }
          servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
          AnnotationAwareOrderComparator.sort(initializers);
          for (WebApplicationInitializer initializer : initializers) {
              initializer.onStartup(servletContext);
          }
     }
}

 

Interface implementation class WebApplicationInitializer.class

public abstract class SpringBootServletInitializer implements WebApplicationInitializer {
......
     @Override
     public void onStartup(ServletContext servletContext) throws ServletException {
          // Logger initialization is deferred in case an ordered
          // LogServletContextInitializer is being used
          this.logger = LogFactory.getLog(getClass());
          WebApplicationContext rootAppContext = createRootApplicationContext(servletContext);
          ......//略去部分代码
     }

     protected WebApplicationContext createRootApplicationContext(
              ServletContext servletContext) {
          SpringApplicationBuilder builder = createSpringApplicationBuilder();
          builder.main(getClass());
          ApplicationContext parent = getExistingRootWebApplicationContext(servletContext);
          ......//略去部分代码
          return run(application);
     }

    protected WebApplicationContext run(SpringApplication application) {
          return (WebApplicationContext) application.run();
     }

}

 

spring boot main application class

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