protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(SpringBootTestApplication.class);
    }

@Controller
public class StartController {

    @GetMapping("/")
    public String index(){
        return "index";
    }
}

<dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </dependency>

        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
        </dependency>

There was an unexpected error (type=Not Found, status=404).
/WEB-INF/views/index.jsp