Spring Boot Controller not mapping

I have used STS and now I am using IntelliJ Ultimate Edition but I am still getting the same output. My controller is not getting mapped thus showing 404 error. I am completely new to Spring Framework.

DemoApplication.java

package com.webservice.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
public class DemoApplication {

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

HelloController.java

package com.webservice.demo;


import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @RequestMapping("/hello")
    public String sayHello(){
        return "Hey";
    }

}

Console Output

com.webservice.demo.DemoApplication      : Starting DemoApplication on XFT000159365001 with PID 11708 (started by Mayank Khursija in C:UsersMayank KhursijaIdeaProjectsdemo)
    2017-07-19 12:59:46.150  INFO 11708 --- [           main] com.webservice.demo.DemoApplication      : No active profile set, falling back to default profiles: default
    2017-07-19 12:59:46.218  INFO 11708 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@238e3f: startup date [Wed Jul 19 12:59:46 IST 2017]; root of context hierarchy
    2017-07-19 12:59:47.821  INFO 11708 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8211 (http)
    2017-07-19 12:59:47.832  INFO 11708 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
    2017-07-19 12:59:47.832  INFO 11708 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.15
    2017-07-19 12:59:47.944  INFO 11708 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
    2017-07-19 12:59:47.944  INFO 11708 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1728 ms
    2017-07-19 12:59:47.987  INFO 11708 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
    2017-07-19 12:59:48.510  INFO 11708 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
    2017-07-19 12:59:48.519  INFO 11708 --- [           main] o.s.c.support.DefaultLifecycleProcessor  : Starting beans in phase 0
    2017-07-19 12:59:48.634  INFO 11708 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8211 (http)
    2017-07-19 12:59:48.638  INFO 11708 --- [           main] com.webservice.demo.DemoApplication      : Started DemoApplication in 2.869 seconds (JVM running for 3.44)

Answer

I too had the similar issue and was able to finally resolve it by correcting the source package structure following this

Your Controller classes are not scanned by the Component scanning. Your Controller classes must be nested below in package hierarchy to the main SpringApplication class having the main() method, then only it will be scanned and you should also see the RequestMappings listed in the console output while Spring Boot is getting started.

Tested on Spring Boot 1.5.8.RELEASE

But in case you prefer to use your own packaging structure, you can always use the @ComponentScan annotation to define your basePackages to scan.