Spring MVC-1 TIL (3)

[참고 강의] 김영한님의 스프링 MVC 1편 - 백엔드 웹 개발 핵심 기술

💡 서블릿 - HTTP 요청 데이터

✏️ API 메시지 바디 - 단순 텍스트

HTTP message body에 데이터를 직접 담아서 요청

• HTTP API에서 주로 사용, JSON, XML, TEXT
• 데이터 형식은 주로 JSON사용
• POST, PUT, PATCH

먼저 가장 단순한 텍스트 메시지를 HTTP 메시지 바디에 담아서 전송하고, 읽어보자.
HTTP 메시지 바디의 데이터를 inputStream을 사용해서 직접 읽을 수 있다.

@WebServlet(name = "requestBodyStringServlet", urlPatterns = "/request-body-string")
public class RequestBodyStringServlet extends HttpServlet {

      @Override
      protected void service(HttpServletRequest request, HttpServletResponse response)
              throws ServletException, IOException {
              
          ServletInputStream inputStream = request.getInputStream();
          String messageBody = StreamUtils.copyToString(inputStream,
  StandardCharsets.UTF_8);
  
          System.out.println("messageBody = " + messageBody);
          
          response.getWriter().write("ok");
      }
}

문자 전송

• POST http://localhost:8080/request-body-string
• content-type: text/plain
• message body: hello
• 결과: messageBody = hello

✏️ API 메시지 바디 - JSON

HTTP API에서 주로 사용하는 JSON 형식으로 데이터를 전달해보자.

• POST http://localhost:8080/request-body-json
• content-type: application/json
• message body: {"username": "hello", "age": 20}
• 결과: messageBody = {"username": "hello", "age": 20}

객체 생성

@Getter @Setter
public class HelloData {

      private String username;
      private int age;
      
}

@WebServlet(name = "requestBodyJsonServlet", urlPatterns = "/request-body-json")
public class RequestBodyJsonServlet extends HttpServlet {

        private ObjectMapper objectMapper = new ObjectMapper();
        
        @Override
        protected void service(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
                
            ServletInputStream inputStream = request.getInputStream();
            
            String messageBody = StreamUtils.copyToString(inputStream, StandardCharsets.UTF_8);
    
            System.out.println("messageBody = " + messageBody);
            HelloData helloData = objectMapper.readValue(messageBody, HelloData.class);
            
            System.out.println("helloData.username = " + helloData.getUsername());
            System.out.println("helloData.age = " + helloData.getAge());
            
            response.getWriter().write("ok");
        }
}

출력 결과

    messageBody={"username": "hello", "age": 20}
    data.username=hello
    data.age=20

✏️ HttpServletResponse - 기본 사용법

HTTP 응답 메시지 생성

• HTTP 응답코드 지정
• 헤더 생성
• 바디 생성

@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");

}

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");
}

✏️ HTTP 응답 데이터 - 단순 텍스트, HTML

HttpServletResponse - HTML 응답

Content-type을 text/html로 지정해야함

@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>");
     } 
}

API JSON 응답 데이터

content-type을 application/json으로 지정해야 한다.
Jackson 라이브러리가 제공하는 objectMapper.writeValueAsString()를 사용하면 객체를 JSON 문자로 변경할 수 있다.

@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);
      } 
}

진짜 강의 곧 폭주해서 들어야겠당..!!!!