중복확인을 조금 더 안정적으로 하기 위해서 AjaxController package com.itwillbs.controller; import javax.inject.Inject; import javax.servlet.http.HttpServletResponse; import org.springframework.http.HttpStatus; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; import com.itwillbs.domain.MemberDTO;.....