w3schools.com -> Bootstrap 4 -> BootStap4 Navbar

https://www.w3schools.com/bootstrap4/bootstrap_navbar.asp

Collapsing The Navigation Bar 사용

index.jsp -> header.jsp, footer.jsp 분할

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boardController 생성 - > index 이동

package com.cos.blog.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class BoardController {

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