ServletContextListener获得spring注入的bean对象

public class SystemInitListener implements ServletContextListener {
    private Logger logger = LoggerFactory.getLogger(getClass());
    private CityService cityService;
    private WebApplicationContext webApplicationContext;

    public void setCityService(CityService cityService) {
        this.cityService = cityService;
    }

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        if(null == webApplicationContext){
            webApplicationContext = WebApplicationContextUtils.getWebApplicationContext(servletContextEvent.getServletContext());
            if(null != webApplicationContext){
                cityService = (CityService)webApplicationContext.getBean("cityService");
            }
        }
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}