2-3. HTTP 응답 데이터

shin·2025년 4월 6일

Spring MVC

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1) HttpServletResponse 역할

HTTP 응답 메시지 생성

HTTP 응답 코드 지정

헤더 생성

바디 생성

편의 기능 제공

Content-Type, 쿠키, Redirect

2) 기본 사용법

hello.servlet.basic.response.ResponseHeaderServlet

package hello.servlet.basic.response;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
 
/**
* http://localhost:8080/response-header
*
*/
@WebServlet(name = "responseHeaderServlet", urlPatterns = "/response-header")
public class ResponseHeaderServlet extends HttpServlet {
    
    @Override
 	protected void service(HttpServletRequest request, HttpServletResponse response)  throws ServletException, IOException {
    
		//[status-line]
        response.setStatus(HttpServletResponse.SC_OK); //200
 		
        //[response-headers]
        response.setHeader("Content-Type", "text/plain;charset=utf-8");
        response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
        response.setHeader("Pragma", "no-cache");
        response.setHeader("my-header","hello");
        
 		//[Header 편의 메서드]
 		content(response);
 		cookie(response);
 		redirect(response);
        
 		//[message body]
 		PrintWriter writer = response.getWriter();
        writer.println("ok");
    }
 }

Content 편의 메서드

private void content(HttpServletResponse response) {

	//Content-Type: text/plain;charset=utf-8
 	//Content-Length: 2
 	//response.setHeader("Content-Type", "text/plain;charset=utf-8");
    response.setContentType("text/plain");
    response.setCharacterEncoding("utf-8");
 	//response.setContentLength(2); //(생략시 자동 생성)
 }

쿠키 편의 메서드

private void cookie(HttpServletResponse response) {

 	//Set-Cookie: myCookie=good; Max-Age=600;
 	//response.setHeader("Set-Cookie", "myCookie=good; Max-Age=600");
 	Cookie cookie = new Cookie("myCookie", "good");
    cookie.setMaxAge(600); //600초
    response.addCookie(cookie);
}

redirect 편의 메서드

private void redirect(HttpServletResponse response) throws IOException {

 	//Status Code 302
 	//Location: /basic/hello-form.html
 	//response.setStatus(HttpServletResponse.SC_FOUND); //302
 	//response.setHeader("Location", "/basic/hello-form.html");
    response.sendRedirect("/basic/hello-form.html");
 }

3) HTTP 응답 데이터

HTTP 응답 메시지는 주로 다음 내용을 담아서 전달함
단순 텍스트 응답
- 앞에서 살펴봄(write.println("ok"))
HTML 응답
HTMP API - MessageBody JSON 응답

(1) HttpServletResponse - HTML 응답

hello.servlet.web.response.ResponseHtmlServlet

package hello.servlet.basic.response;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "responseHtmlServlet", urlPatterns = "/response-html")
public class ResponseHtmlServlet extends HttpServlet {
    
    @Override
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
 		//Content-Type: text/html;charset=utf-8
        response.setContentType("text/html");
        response.setCharacterEncoding("utf-8");
        
 		PrintWriter writer = response.getWriter();
        writer.println("<html>");
        writer.println("<body>");
        writer.println("  <div>안녕?</div>");
        writer.println("</body>");
        writer.println("</html>");
    }
}

HTTP 응답으로 HTML을 반환할 때는 content-type을 text/html로 지정해야 함

실행

http://localhost:8080/response-html
페이지 소스보기를 사용하면 결과 HTML을 확인할 수 있음

4) HTTP 응답 데이터 - API JSON

hello.servlet.response.ResponseJsonServlet

package hello.servlet.basic.response;

import com.fasterxml.jackson.databind.ObjectMapper; import hello.servlet.basic.HelloData;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * http://localhost:8080/response-json
 *
 */
@WebServlet(name = "responseJsonServlet", urlPatterns = "/response-json")
public class ResponseJsonServlet extends HttpServlet {

	private ObjectMapper objectMapper = new ObjectMapper();

    @Override
 	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
 		//Content-Type: application/json
        response.setHeader("content-type", "application/json");
        response.setCharacterEncoding("utf-8");
        
 		HelloData data = new HelloData();
        data.setUsername("kim");
        data.setAge(20);
        
 		//{"username":"kim","age":20}
 		String result = objectMapper.writeValueAsString(data);
        
        response.getWriter().write(result);
    }
 }

HTTP 응답으로 JSON을 반환할 때는 content-type을 application/json으로 지정해야 함
jackson 라이브러리가 제공하는 objectMapper.writeValueAsString()를 사용하면 객체를 JSON 문자로 변환할 수 있음

실행

http://localhost:8080/response-json

참고

application/json은 스펙상 utf-8 형식을 사용하도록 정의되어 있음
- 그래서 스펙에서 charset=utf-8과 같은 추가 파라미터를 지원하지 않음
- 따라서 application/json이라고만 사용해야지 application/json;charset=utf-8이라고 전달하는 것은 의미없는 파라미터를 추가한 것이 됨
response.getWriter()를 사용하면 추가 파라미터를 자동으로 추가해버림
- 이때는 response.getOutputStream()으로 출력하면 그런 문제는 발생하지 않음