Spring boot demo application class

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.core.env.Environment;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
public class DemoApplication {

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

}

@RestController
@RequestMapping("/")
class DemoController {

    private final Environment env;

    DemoController(Environment env) {
        this.env = env;
    }

    @GetMapping
    public String sayHi() {
        return "Hi from Demo application with port: " + env.getProperty("local.server.port");
    }
}