where should I put RestController in spring boot project

I used idea IDE to developed a Java springboot project follow a tutorial.
However, in the tutorial, there's a function shown below. I do not know where to put this function in me spring boot project.
The function:

package com.helloworld.controller;

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

/**
 * Created by fangxiao on 2017/3/24.
 */
@RestController
public class Controller {

    @RequestMapping("/helloworld")
    public String helloWorld() {
        return "helloworld";
    }
}

where should I put this function as for the below project structure?<br/>
project structure

Following your example, the Controller Class have a organization like this picture:

I also created another packages that are frequentelly used in a spring-boot project

Since your package is :

package com.helloworld.controller;

You can create folder structure inside java folder com -> helloworld -> controller and keep the code (Controller.java class) inside.

Create a package under src/main/java like com.abc.rest and create RestController class
:Here is the sample code and to access this api use url like : localhost:8080/test/headers

@RestController
@RequestMapping(value = "/test", produces = MediaType.APPLICATION_JSON_VALUE)
public class Rest {
	
	@GetMapping("/headers")
	public String listAllHeaders(@RequestHeader Map<String, String> headers) {
	    headers.forEach((key, value) -> {
	        System.out.println(String.format("Header '%s' = %s", key, value));
	    });
	 return "success";
	}
}

For learning purpose is good to do it manually, but if you want to skip it, you can create the class shown above in the src/main/java and IntelliJ will dectect and offer to relocate it to the proper package.

Create your package com.project.controller under

> D:\Bill\java\test\src\main\java

directory