[스프링 MVC 1편] 2. 서블릿 (3)

HttpServletResponse - 기본 사용법

HttpServletResponse 역할

• HTTP 응답 메시지 생성
  - HTTP 응답코드 지정
  - 헤더 생성
  - 바디 생성
• 편의 기능 제공
  - Content-Type, 쿠키, Redirect
  

ResponseHeaderServlet

@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"); //content 메서드에서 수행
        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"); //위 두 줄(setStatus, setHeader)의 기능을 수행
    }

실행 결과

HTTP 응답 데이터 - JSON

ResponseJsonServlet

@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.setContentType("application/json");
        response.setCharacterEncoding("utf-8");

        HelloData helloData = new HelloData();
        helloData.setUsername("maeng");
        helloData.setAge(26);

        //{"username":"maeng", "age":26}
        String result = objectMapper.writeValueAsString(helloData);

        response.getWriter().write(result);
    }
}

Jackson 라이브러리가 제공하는 ObjectMapper를 사용하면 객체를 JSON 문자로 변경할 수 있다. (Request에서도 사용했었음)

실행 결과

Reference

https://www.inflearn.com/course/%EC%8A%A4%ED%94%84%EB%A7%81-mvc-1/dashboard