There was an unexpected error (type=Internal Server Error, status=500).
Error resolving template "form", template might not exist or might not be accessible by any of the configured Template Resolvers

package test.config;

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

@EnableAutoConfiguration
@EnableWebMvc
@ComponentScan("test")
public class Application {

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

}

package test.config;

import org.springframework.context.annotation.*;
import org.springframework.web.servlet.config.annotation.*;
import org.springframework.web.servlet.view.*;

@Configuration
@EnableWebMvc
@ComponentScan
public class WebConfig extends WebMvcConfigurerAdapter {

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/WEB-INF/pages/**").addResourceLocations("/pages/");
    }

    @Bean
    public InternalResourceViewResolver getViewResolver() {
        InternalResourceViewResolver resolver = new InternalResourceViewResolver();
        resolver.setPrefix("/WEB-INF/pages/");
        resolver.setSuffix(".jsp");
        resolver.setViewClass(JstlView.class);

        return resolver;
    }

    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        configurer.enable();
    }

}

@Controller
public class WebController extends WebMvcConfigurerAdapter {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/results").setViewName("results");
    }

    @RequestMapping(value="/", method=RequestMethod.GET)
    public String showForm(Person person) {
        return "form";
    }

    @RequestMapping(value="/", method=RequestMethod.POST)
    public String checkPersonInfo(@Valid Person person, BindingResult bindingResult) {
        if (bindingResult.hasErrors()) {
            return "form";
        }
        return "redirect:/results";
    }

}

@Configuration
@EnableWebMvc
public class AppConfig extends WebMvcConfigurerAdapter  {
    @Bean
    public EmbeddedServletContainerFactory servletContainer() {
        TomcatEmbeddedServletContainerFactory factory =
                new TomcatEmbeddedServletContainerFactory();
        return factory;
    }
    //start Thymeleaf specific configuration
    @Bean(name ="templateResolver")
    public ServletContextTemplateResolver getTemplateResolver() {
        ServletContextTemplateResolver templateResolver = new ServletContextTemplateResolver();
        templateResolver.setPrefix("/WEB-INF/templates/");
        templateResolver.setSuffix(".html");
        templateResolver.setTemplateMode("XHTML");
        return templateResolver;
    }
    @Bean(name ="templateEngine")
    public SpringTemplateEngine getTemplateEngine() {
        SpringTemplateEngine templateEngine = new SpringTemplateEngine();
        templateEngine.setTemplateResolver(getTemplateResolver());
        return templateEngine;
    }
    @Bean(name="viewResolver")
    public ThymeleafViewResolver getViewResolver(){
        ThymeleafViewResolver viewResolver = new ThymeleafViewResolver();
        viewResolver.setTemplateEngine(getTemplateEngine());
        return viewResolver;
    }
    //end Thymeleaf specific configuration
    @Bean(name ="messageSource")
    public MessageSource getMessageSource() {
        ReloadableResourceBundleMessageSource messageSource = new ReloadableResourceBundleMessageSource();
        messageSource.setBasename("/WEB-INF/i18/blogmsg");
        messageSource.setDefaultEncoding("UTF-8");
        return messageSource;
    }
}

public class WebAppInitializer implements WebApplicationInitializer {

    public void onStartup(ServletContext servletContext) throws ServletException {
        System.out.println("===============================================================");
        AnnotationConfigWebApplicationContext ctx = new AnnotationConfigWebApplicationContext();
        ctx.register(AppConfig.class);
        ctx.setServletContext(servletContext);
        Dynamic dynamic = servletContext.addServlet("dispatcher", new DispatcherServlet(ctx));
        dynamic.addMapping("/");
        dynamic.setLoadOnStartup(1);
    }
}

@ComponentScan("test")
public class Application {

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

}

Spring boot - Это уж совсем когда нужно быстро ... и не в даваясь в подробности ... в 90% он удовлетворяет всем потребностям чтобы не вдаваться в подробности - из серии взял и используй ...но иногда шаг влево шаг в право и все затырка ...и тут нужно оооочень хорошо понимать как это работает и как устроено .... на понимание можно и больше времени потратить ...