서블릿이란 (JSON, HttpServletRequest, HttpServletResponse)

서블릿

• 서블릿 사용을 위한 프로젝트 WAR, 롬복, 스프링 웹 설치

@ServletComponentScan // 서블릿 자동 등록 
@SpringBootApplication
public class HelloApplication {

    public static void main(String[] args) {
        SpringApplication.run(HelloApplication.class, args);
    }

}

----------------http://localhost:8080/hello?username=kim url 입력
@WebServlet(name = "helloServlet", urlPatterns = "/hello")
public class HelloServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("HelloServlet.service");

        System.out.println("request = " + request);
        System.out.println("response = " + response);
        String username = request.getParameter("username");
        System.out.println("username = " + username);

        response.setContentType("text/plain");
        response.setCharacterEncoding("utf-8");
        response.getWriter().write("hello "+username); //응답
    }
}
--------------------------------------------------------------------------
HelloServlet.service
request = org.apache.catalina.connector.RequestFacade@2eb7a3e1
response = org.apache.catalina.connector.ResponseFacade@61cdd749
username = kim

• ctrl + o 를 통해 service 상속 메서드 생성

• 응답 헤더를 확인 (F12 - Network- Headers)

// application.properties에 설정시 로그를 찍어볼 수 있다.
logging.level.org.apache.coyote.http11=debug

HttpServletRequest

@WebServlet(name = "requestHeaderServlet", urlPatterns = "/request-header")
public class RequestHeaderServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       printStartLine(request);
       printHeaderUtils(request);
       printEtc(request);
    }

    private void printStartLine(HttpServletRequest request) {
        System.out.println("--- REQUEST-LINE - start ---");
        System.out.println("request.getMethod() = " + request.getMethod()); //GET
        System.out.println("request.getProtocal() = " + request.getProtocol()); // HTTP/1.1
        System.out.println("request.getScheme() = " + request.getScheme()); //http
        // http://localhost:8080/request-header
        System.out.println("request.getRequestURL() = " + request.getRequestURL());
        // /request-test
        System.out.println("request.getRequestURI() = " + request.getRequestURI());
        //username=hi
        System.out.println("request.getQueryString() = " + request.getQueryString());
        System.out.println("request.isSecure() = " + request.isSecure()); //https 사용 유무
        System.out.println("--- REQUEST-LINE - end ---");
        System.out.println();
    }
    private void printHeaderUtils(HttpServletRequest request) {

        System.out.println("--- Header 편의 조회 start ---");
        System.out.println("[Host 편의 조회]");
        System.out.println("request.getServerName() = " +  request.getServerName()); //Host 헤더
        System.out.println("request.getServerPort() = " +  request.getServerPort()); //Host 헤더
        System.out.println();
        System.out.println("[Accept-Language 편의 조회]");
        request.getLocales().asIterator()
                .forEachRemaining(locale -> System.out.println("locale = " +
                        locale));
        System.out.println("request.getLocale() = " + request.getLocale());
        System.out.println();
        System.out.println("[cookie 편의 조회]");
        if (request.getCookies() != null) {
            for (Cookie cookie : request.getCookies()) {
                System.out.println(cookie.getName() + ": " + cookie.getValue());
            }
        }
        System.out.println();
        System.out.println("[Content 편의 조회]");
        System.out.println("request.getContentType() = " +
                request.getContentType());
        System.out.println("request.getContentLength() = " +
                request.getContentLength());
        System.out.println("request.getCharacterEncoding() = " +
                request.getCharacterEncoding());
        System.out.println("--- Header 편의 조회 end ---");
        System.out.println();
    }

    private void printEtc(HttpServletRequest request) {
        System.out.println("--- 기타 조회 start ---");
        System.out.println("[Remote 정보]");
        System.out.println("request.getRemoteHost() = " +  request.getRemoteHost()); //
        System.out.println("request.getRemoteAddr() = " +  request.getRemoteAddr()); //
        System.out.println("request.getRemotePort() = " +  request.getRemotePort()); //
        System.out.println();
        System.out.println("[Local 정보]");
        System.out.println("request.getLocalName() = " +   request.getLocalName()); //
        System.out.println("request.getLocalAddr() = " +   request.getLocalAddr()); //
        System.out.println("request.getLocalPort() = " +   request.getLocalPort()); //
        System.out.println("--- 기타 조회 end ---");
        System.out.println();
    }
}

• HttpServletRequest를 통해 start-line, header 정보 조회

HTTP 요청 데이터

• HTTP 요청 메시지를 통해 클라이언트에서 서버로 데이터를 전달하는 방법 3가지
• GET - 쿼리 파라미터
  • 메시지 바디 없이 URL에 쿼리 파라미터에 데이터를 포함해서 전달
  • /url?username=hello&age=20
• POST - HTML Form
  • content-type: application/x-www-form-urlencoded
  • 메시지 바디에 쿼리 파리미터 형식으로 전달 username=hello&age=20
• HTTP message body에 직접 담아서 요청
  • HTTP API에서 주로 사용, JSON, XML, TEXT (데이터 형식은 주로 JSON 사용)

GET - 쿼리파라미터

// http://localhost:8080/request-param?username=hello&age=20
@WebServlet(name = "requestParamServlet", urlPatterns = "/request-param")
public class RequestParamServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("[전체 파라미터 조회] - start");

        request.getParameterNames().asIterator()
                .forEachRemaining(paramName -> System.out.println(paramName + "=" + request.getParameter(paramName)));

        System.out.println("[전체 파라미터 조회] - end");
        System.out.println();

        System.out.println("[단일 파라미터 조회]");
        String username = request.getParameter("username");
        String age = request.getParameter("age");

        System.out.println("username = " + username);
        System.out.println("age = " + age);

        System.out.println("[이름이 같은 복수 파라미터 조회]");
        String[] usernames = request.getParameterValues("username");
        for (String name : usernames) {
            System.out.println("name = " + name);
        }

        response.getWriter().write("ok");
    }
}

POST - HTML Form

• content-type: application/x-www-form-urlencoded를 꼭 지정해주어야 한다.
• 메시지 바디에 쿼리 파리미터 형식으로 데이터를 전달한다. username=hello&age=20
• request.getParameter()는 Get 쿼리 파라미터, Post Html Form 형식 둘다 지원한다.

HTTP message body에 직접 담아서 요청

• HTTP API에서 주로사용 주로 JSON
• POST, PUT, PATCH 주로 사용

단순 텍스트

@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");
    }
}

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

JSON 형식

import com.fasterxml.jackson.databind.ObjectMapper;
import hello.servlet.basic.HelloData;
import org.springframework.util.StreamUtils;
import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
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.nio.charset.StandardCharsets;

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

    //json 라이브러리 Jackson MVC는 기본 제공 
    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.getUsername() = " + helloData.getUsername());
        System.out.println("helloData.getAge() = " + helloData.getAge());

        response.getWriter().write("ok");
    }
}

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

HttpServletResponse

• HTTP 응답 메시지 생성
  • HTTP 응답 코드 지정
  • 헤더, 바디 생성
• Content-Type, 쿠키, Redirect

@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); // 상태코드 200 성공

        //[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);

        PrintWriter writer = response.getWriter();
        writer.println("안녕하세요"); // println 이들어가면 \n 이 포함되어 Content-Length 2증가
    }

    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)
    }

    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);
    }

    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");
    }
}

HTML 응답

@WebServlet(name = "responseHtmlServlet", urlPatterns = "/response-html")
public class ResponseHtmlServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        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>");
    }
}

 

JSON 응답

@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);
    }
}

 

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본 포스팅은 인프런 김영한님 강의(스프링 MVC 1편 - 백엔드 웹 개발 핵심 기술)를 토대로 정리한 내용입니다.