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HTTP 응답 데이터(HttpServletResponse) - 단순 텍스트, HTML, HTTP API JSON

먹태 2021. 4. 21. 23:21

HttpServletResponse역할

- Htttp 응답 메세지 생성 (HTTP응답코드 지정, 헤더생성 ,바디생성)

- 편의 기능 제공(Content-Type, 쿠키, Redirect)

 

 

 

0. HttpServletResponse 사용법

ResponseHeaderServlet.java

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;

@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);

        //[response-headers]
        response.setHeader("Content-Type", "text/plain;charset=utf-8");
        response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); //캐시무효화
        response.setHeader("Pragma", "no-cache");
        response.setHeader("my-header", "hello");


        //[Header 편의 메서드]
        //content(response);
        //cookie( response);
        //redirect(response);
        
        PrintWriter writer = response.getWriter();
        writer.println("초밥먹고싶당");
    }
}

 

 

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");
  }

 

 

 

1.  HTTP 응답 데이터 - 단순 텍스트 응답

 -writer.println("oK");

 

 

 

2.  HTTP 응답 데이터 - HTML 응답

 

ResponseHtmlServlet.java

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>");
 }
}

- html로 반환할때는 content-type을 text/html 로 지정해야함

 

 

실행결과↓

 

 

 

3. HTTP 응답 데이터 - API JSON

 

ResponseJsonServlet.java

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;

@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 {


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

        HelloData helloData = new HelloData();
        helloData.setUsername("Kim");
        helloData.setAge(20);

        ////{"username":"kim","age":20}
        String result = objectMapper.writeValueAsString(helloData);
        response.getWriter().write(result);
    }
}

- HTTP 응답으로 JSON을 반환할 때는 content-type을 application/json 로 지정

- Jackson 라이브러리가 제공하는 objectMapper.writeValueAsString() 를 사용하면 객체를 JSON 문자로 변경가능

 

 

실행결과↓

 

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