详解spring注解配置启动过程

@Order(1)
public class WebMvcInit extends AbstractAnnotationConfigDispatcherServletInitializer {
 protected Class<?>[] getRootConfigClasses() {
  return new Class[]{RootConfig.class,WebSecurityConfig.class};
 }

 protected Class<?>[] getServletConfigClasses() {
  return new Class[]{WebConfig.class};
 }

 protected String[] getServletMappings() {
  return new String[]{"/"};
 }

 @Override
 protected Filter[] getServletFilters() {
  return new Filter[]{new HiddenHttpMethodFilter()};
 }

}

@Override
 protected WebApplicationContext createRootApplicationContext() {
  Class<?>[] configClasses = getRootConfigClasses();
  if (!ObjectUtils.isEmpty(configClasses)) {
   AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();
   rootAppContext.register(configClasses);
   return rootAppContext;
  }
  else {
   return null;
  }
 } 

public abstract class AbstractContextLoaderInitializer implements WebApplicationInitializer {

 /** Logger available to subclasses */
 protected final Log logger = LogFactory.getLog(getClass());


 @Override
 public void onStartup(ServletContext servletContext) throws ServletException {
  registerContextLoaderListener(servletContext);
 }

 /**
  * Register a {@link ContextLoaderListener} against the given servlet context. The
  * {@code ContextLoaderListener} is initialized with the application context returned
  * from the {@link #createRootApplicationContext()} template method.
  * @param servletContext the servlet context to register the listener against
  */
 protected void registerContextLoaderListener(ServletContext servletContext) {
  WebApplicationContext rootAppContext = createRootApplicationContext();
  if (rootAppContext != null) {
   ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
   listener.setContextInitializers(getRootApplicationContextInitializers());
   servletContext.addListener(listener);
  }
  else {
   logger.debug("No ContextLoaderListener registered, as " +
     "createRootApplicationContext() did not return an application context");
  }
 }

 /**
  * Create the "<strong>root</strong>" application context to be provided to the
  * {@code ContextLoaderListener}.
  * <p>The returned context is delegated to
  * {@link ContextLoaderListener#ContextLoaderListener(WebApplicationContext)} and will
  * be established as the parent context for any {@code DispatcherServlet} application
  * contexts. As such, it typically contains middle-tier services, data sources, etc.
  * @return the root application context, or {@code null} if a root context is not
  * desired
  * @see org.springframework.web.servlet.support.AbstractDispatcherServletInitializer
  */
 protected abstract WebApplicationContext createRootApplicationContext();

 /**
  * Specify application context initializers to be applied to the root application
  * context that the {@code ContextLoaderListener} is being created with.
  * @since 4.2
  * @see #createRootApplicationContext()
  * @see ContextLoaderListener#setContextInitializers
  */
 protected ApplicationContextInitializer<?>[] getRootApplicationContextInitializers() {
  return null;
 }

}

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
 @Override
 public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
   throws ServletException {

  List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();

  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) 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);
  }
 }

}