在@EnableWebMvc注解并且继承WebMvcConfigurerAdapter类的配置中重写addViewControllers方法：
@EnableWebMvc
@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void addViewControllers(ViewControllerRegistry registry) {
//设置默认首页
registry.addViewController("/").setViewName("index");
registry.setOrder( Ordered.HIGHEST_PRECEDENCE );
super.addViewControllers(registry);
}
}