Add context path to Spring Boot application

I am trying to set a Spring Boot applications context root programmatically. The reason for the context root is we want the app to be accessed from localhost:port/{app_name} and have all the controller paths append to it.

Here is the application configuration file for the web-app.

@Configuration
public class ApplicationConfiguration {

  Logger logger = LoggerFactory.getLogger(ApplicationConfiguration.class);

  @Value("${mainstay.web.port:12378}")
  private String port;

  @Value("${mainstay.web.context:/mainstay}")
  private String context;

  private Set<ErrorPage> pageHandlers;

  @PostConstruct
  private void init(){
      pageHandlers = new HashSet<ErrorPage>();
      pageHandlers.add(new ErrorPage(HttpStatus.NOT_FOUND,"/notfound.html"));
      pageHandlers.add(new ErrorPage(HttpStatus.FORBIDDEN,"/forbidden.html"));
  }

  @Bean
  public EmbeddedServletContainerFactory servletContainer(){
      TomcatEmbeddedServletContainerFactory factory = new TomcatEmbeddedServletContainerFactory();
      logger.info("Setting custom configuration for Mainstay:");
      logger.info("Setting port to {}",port);
      logger.info("Setting context to {}",context);
      factory.setPort(Integer.valueOf(port));
      factory.setContextPath(context);
      factory.setErrorPages(pageHandlers);
      return factory;
  }

  public String getPort() {
      return port;
  }

  public void setPort(String port) {
      this.port = port;
  }
}

Here is the index controller for the main page.

@Controller
public class IndexController {

  Logger logger = LoggerFactory.getLogger(IndexController.class);

  @RequestMapping("https://stackoverflow.com/")
  public String index(Model model){
      logger.info("Setting index page title to Mainstay - Web");
      model.addAttribute("title","Mainstay - Web");
      return "index";
  }

}

The new root of the application should be at localhost:12378/mainstay, but it is still located at localhost:12378.

What am I missing that is causing Spring Boot to not append the context root before the request mapping?