[Spring] HTTP Servlet

jinsung·2026년 7월 3일

Spring

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@ServletComponentScan

스프링 부트는 서블릿을 직접 등록해서 사용할 수 있도록 @ServletComponentScan 을 지원

@WebServlet 서블릿 애노테이션

  • name: 서블릿 이름
  • urlPatterns: URL 매핑

HttpServletRequest 역할

임시 저장소 기능

해당 HTTP 요청이 시작부터 끝날 때 까지 유지되는 임시 저장소 기능

  • 저장: request.setAttribute(name, value)
  • 조회: request.getAttribute(name)

세션 관리 기능

request.getSession(create: true)

HttpServletRequest 헤더, 기타정보 조회

package hello.servlet.basic.request;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.Cookie;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.Enumeration;

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

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

        printStartLine(request);
        printHeaders(request);
        printHeaderUtils(request);
        printEtc(request);
    }

    //start line 정보
    private void printStartLine(HttpServletRequest request) {
        System.out.println("--- REQUEST-LINE - start ---");
        System.out.println("request.getMethod() = " + request.getMethod()); //GET
        System.out.println("request.getProtocol() = " + 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-header
        System.out.println("request.getRequestURI() = " + request.getRequestURI());
        //username=hi
        System.out.println("request.getQueryString() = " +
                request.getQueryString());
        System.out.println("request.isSecure() = " + request.isSecure()); //https 사용유무
        System.out.println("--- REQUEST-LINE - end ---");
        System.out.println();
    }

    //Header 모든 정보
    private void printHeaders(HttpServletRequest request) {
        System.out.println("--- Headers - start ---");
/*
         Enumeration<String> headerNames = request.getHeaderNames();
         while (headerNames.hasMoreElements()) {
            String headerName = headerNames.nextElement();
            System.out.println(headerName + ": " + request.getHeader(headerName));
         }

 */

        request.getHeaderNames().asIterator()
                .forEachRemaining(headerName -> System.out.println(headerName + ": "
                        + request.getHeader(headerName)));

        System.out.println("--- Headers - end ---");
        System.out.println();
    }

    //Header 편리한 조회
    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 ---");
    }

    //기타 정보
    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();
    }
}

HTTP 요청 데이터

클라이언트 -> 서버 보내는 방법

GET - 쿼리 파라미터

  • /url?username=hello&age=20
  • 메시지 바디 없이, URL의 쿼리 파라미터에 데이터를 포함해서 전달
  • 예) 검색, 필터, 페이징등에서 많이 사용하는 방식
package hello.servlet.basic.request;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.Enumeration;

@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");

 /*     Enumeration<String> parameterNames = request.getParameterNames();
        while (parameterNames.hasMoreElements()) {
           String paramName = parameterNames.nextElement();
           System.out.println(paramName + "=" +
           request.getParameter(paramName));
        }
 */

        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");
        System.out.println("request.getParameter(username) = " + username);
        String age = request.getParameter("age");
        System.out.println("request.getParameter(age) = " + age);
        System.out.println();
        System.out.println("[이름이 같은 복수 파라미터 조회]");
        System.out.println("request.getParameterValues(username)");
        String[] usernames = request.getParameterValues("username");

        for (String name : usernames) {
            System.out.println("username=" + name);
        }
        response.getWriter().write("ok");
    }
}

POST - HTML Form

  • content-type: application/x-www-form-urlencoded
  • 메시지 바디에 쿼리 파리미터 형식으로 전달 username=hello&age=20
  • 예) 회원 가입, 상품 주문, HTML Form 사용
<!DOCTYPE html>
<html>
<head>
   <meta charset="UTF-8">
   <title>Title</title>
</head>
<body>

<form action="/request-param" method="post">
   username: <input type="text" name="username" />
   age: <input type="text" name="age" />
   <button type="submit">전송</button>
</form>
</body>
</html>

HTTP message body에 데이터를 직접 담아서 요청

  • HTTP API에서 주로 사용, JSON, XML, TEXT
  • 데이터 형식은 주로 JSON 사용
  • POST, PUT, PATCH
package hello.servlet.basic.request;

import hello.servlet.basic.HelloData;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletInputStream;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.util.StreamUtils;
import tools.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.nio.charset.StandardCharsets;

@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.getUsername() = " + helloData.getUsername());
        System.out.println("helloData.getAge() = " + helloData.getAge());
    }
}

HttpServletResponse 역할

HTTP 응답 메시지 생성

  • HTTP 응답코드 지정
  • 헤더 생성
  • 바디 생성

편의 기능 제공

  • Content-Type, 쿠키, Redirect
package hello.servlet.basic.response;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.Cookie;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.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 {
        response.setStatus(HttpServletResponse.SC_OK);

        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", "hihi");

        content(response);
        cookie(response);
        redirect(response);

        PrintWriter writer = response.getWriter();
        writer.write("ok");

    }

    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;charset=UTF-8");
        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");
    }
}

HTTP 응답 데이터

  • 단순 텍스트 응답
  • HTML 응답
  • HTTP API - MessageBody JSON 응답
package hello.servlet.basic.response;

import hello.servlet.basic.HelloData;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import tools.jackson.databind.ObjectMapper;

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;charset=UTF-8");

        HelloData helloData = new HelloData();
        helloData.setUsername("ham");
        helloData.setAge(25);

        String result = objectMapper.writeValueAsString(helloData);
        response.getWriter().println(result);
    }
}
profile
jinsung
Backend Engineer
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