[스프링 MVC 1편] 서블릿

우나·2022년 11월 25일

Spring

스프링 MVC 1편 - 백엔드 웹 개발 핵심 기술

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프로젝트 생성

Jar가 아니라 War 선택! Jar는 톰캣이 내장되어 있어서 War는 톰캣 서버를 별도로 설치해 사용할 때 사용한다. JSP를 사용하려면 War를 선택해줘야 함

Lombok 설정

Settings -> plugins 에서 Lombok 설치
Settings -> annotation processors 에서 Enable annotation processing 체크

서블릿 등록

/src/main/java/hello.servlet/ServletApplication

package hello.servlet;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;

@ServletComponentScan // 서블릿 자동등록
@SpringBootApplication
public class ServletApplication {

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

}

@ServletComponentScan : 스프링 부트에서 지원, 서블릿 컴포넌트를 자동으로 등록해주는 역할

servlet 만들어보기

request 받아서 response 보내기

/src/main/java/hello.servlet/basic/HelloServlet

package hello.servlet.basic;

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 = "helloServlet", urlPatterns = "/hello")
public class HelloServlet extends HttpServlet {

    // 서블릿 호출하면 service 메소드 호출
    @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);
    }
}

@WebServlet : 서블릿 애노테이션
Ctrl+O 단축키를 사용해서 Service 자동완성
서버를 열고 http://localhost:8080/hello 에 접속해보면

이러한 결과를 볼 수 있다

Parameter 받기

/src/main/java/hello.servlet/basic/HelloServlet

package hello.servlet.basic;

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 = "helloServlet", urlPatterns = "/hello")
public class HelloServlet extends HttpServlet {

    // 서블릿 호출하면 service 메소드 호출
    @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);

    }
}

request에서 Parameter을 받아서 출력
http://localhost:8080/hello?username=kim 에 접속하면 이러한 결과가 나온다

response 메세지 보내기

/src/main/java/hello.servlet/basic/HelloServlet

package hello.servlet.basic;

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 = "helloServlet", urlPatterns = "/hello")
public class HelloServlet extends HttpServlet {

    // 서블릿 호출하면 service 메소드 호출
    @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/palin");
        response.setCharacterEncoding("utf-8");
        response.getWriter().write("hello " + username);
    }
}

setContentType : response 타입 설정
setCharacterEncoding : 문자 인코딩 정보 설정 (대부분 utf-8 사용)
getWriter().write : http 메세지 body에 문자 작성

HttpServletRequest

Http 요청 메세지를 파싱하고 그 결과를 HttpServletRequest 객체에 담아서 제공하는 역할
임시 저장소 기능: request.setAttribute(name, value) 로 저장하고 request.getAtrribute(name)으로 조회할 수 있다
세션 관리 기능: request.getSession(create: true)

StartLine 조회

/src/main/java/hello.servlet/basic/request/RequestHeaderServlet

package hello.servlet.basic.request;

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

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

    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 사용 유무
        System.out.println("--- REQUEST-LINE - end ---");
        System.out.println();
    }
}

/src/main/java/hello.servlet/basic/request/RequestHeaderServlet

package hello.servlet.basic.request;

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;

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

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        printHeaders(request);
        printHeaderUtils(request);
    }
    private void printHeaders(HttpServletRequest request) {
        System.out.println("--- Headers - start ---");
        /* 옛날 방식
        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 ---");
        System.out.println();
    }
}

조회 결과

편의 조회 결과

기타 정보 조회

/src/main/java/hello.servlet/basic/request/RequestHeaderServlet

HTTP 메세지의 정보 X

package hello.servlet.basic.request;

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;

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

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

GET (쿼리 파라미터) : URL에 데이터를 포함해서 전달

POST (HTML Form) :메세지 바디에 쿼리 파라미터 형식으로 전달

HTTP message body : JSON 형식!

GET - 쿼리 파라미터

URL에 쿼리 파라미터를 사용해서 데이터를 포함해서 전달
?username=kim&age=20
?로 시작하고, 추가 파라미터는 &로 구분한다

파라미터 조회

/src/main/java/hello.servlet/basic/request/RequestParamServlet

package hello.servlet.basic.request;

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;

/*
1. 파라미터 전송 기능
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");
        System.out.println("username = " + username);

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

        System.out.println("[이름이 같은 복수 파라미터 조회]");

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

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

request.getParameter()은 하나의 파라미터 이름에 하나의 값만 있을 때 사용해야 하고, 중복일 때는 request.getParameterValues()를 사용해야 한다

POST - HTML Form

/src/main/java/webapp/basic/hello-form

<!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>

이전 GET 실습 코드로 그대로 연결되고 있으나 정상적으로 작동한다 -> 동일한 쿼리 파라미터 형식이기 때문

HTTP message body

단순 텍스트

/src/main/java/hello.servlet/basic/request/RequestBodyStringServlet

package hello.servlet.basic.request;

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 = "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");
    }
}

Postman으로 Text형식을 보내면 정상적으로 출력 되는 것을 확인할 수 있다.

JSON 형식

JSON 형식 파싱 추가

/src/main/java/hello.servlet/basic/HelloData

package hello.servlet.basic;

import lombok.Getter;
import lombok.Setter;

@Getter @Setter
public class HelloData {

    private String username;
    private int age;
}

/src/main/java/hello.servlet/basic/request/RequestBodyJsonServlet

package hello.servlet.basic.request;

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 {

    private final 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);

        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");
    }
}

ObjectMapper : Json 데이터를 파싱해서 자바 객체에 넣을 수 있다 ( 스프링에서 제공 )

HttpServletResponse

HTTP 응답 데이터 생성, Content-type, 쿠키, redirect 등의 역할 수행

/src/main/java/hello.servlet/basic/response/ResponsHeaderServlet

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");
        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("ok");

        //
    }

    private void content(HttpServletResponse response) {
        response.setContentType("text/plain");
        response.setCharacterEncoding("utf-8");
    }

    private void cookie(HttpServletResponse response) {
        Cookie cookie = new Cookie("myCookie", "good");
        cookie.setMaxAge(600); // 600초 유지
        response.addCookie(cookie);
    }

    private void redirect(HttpServletResponse response) throws IOException {
        response.sendRedirect("/basic/hello-form.html");
    }
}

response.setStatus: Http 상태 코드 지정
response.setHeader: Http header 설정, 새로운 header를 만들 수도 있다
cookie.setMaxAge(int) : 초 단위로 쿠키 유지 시간 설정
response.addCookie(cookie) : response에 쿠키 추가
response.sendRedirect("경로") : 지정한 경로로 redirect

HTTP 응답 데이터

단순 텍스트 응답 : writer.println("ok");

HTML 응답

/src/main/java/hello.servlet/basic/response/ResponsHtmlServlet

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>hi</div>");
        writer.println("</body>");
        writer.println("</html>");
    }
}

response로 html을 보내려면, content-type을 text/html로 지정해주어야 한다!

API JSON

/src/main/java/hello.servlet/basic/response/ResponsJsonServlet

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 final 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("kim");
        helloData.setAge(20);

        String result = objectMapper.writeValueAsString(helloData);
        response.getWriter().write(result);
    }
}

response를 json으로 보내려면 content-type을 application/json으로 지정
objectMapper.writeValueAsString() : 객체를 Json으로 변환

우나

다음 포스트

[스프링 MVC 1편] 서블릿

스프링 MVC 1편 - 백엔드 웹 개발 핵심 기술

프로젝트 생성

Lombok 설정

서블릿 등록

/src/main/java/hello.servlet/ServletApplication

servlet 만들어보기

request 받아서 response 보내기

/src/main/java/hello.servlet/basic/HelloServlet

Parameter 받기

/src/main/java/hello.servlet/basic/HelloServlet

response 메세지 보내기

/src/main/java/hello.servlet/basic/HelloServlet

HttpServletRequest

StartLine 조회

/src/main/java/hello.servlet/basic/request/RequestHeaderServlet

Header 조회

/src/main/java/hello.servlet/basic/request/RequestHeaderServlet

기타 정보 조회

/src/main/java/hello.servlet/basic/request/RequestHeaderServlet

HTTP 요청 데이터

GET - 쿼리 파라미터

파라미터 조회

/src/main/java/hello.servlet/basic/request/RequestParamServlet

POST - HTML Form

/src/main/java/webapp/basic/hello-form

HTTP message body

단순 텍스트

/src/main/java/hello.servlet/basic/request/RequestBodyStringServlet

JSON 형식

/src/main/java/hello.servlet/basic/HelloData

/src/main/java/hello.servlet/basic/request/RequestBodyJsonServlet

HttpServletResponse

/src/main/java/hello.servlet/basic/response/ResponsHeaderServlet

HTTP 응답 데이터

HTML 응답

/src/main/java/hello.servlet/basic/response/ResponsHtmlServlet

API JSON

/src/main/java/hello.servlet/basic/response/ResponsJsonServlet

[스프링 MVC 1편] 서블릿, JSP, MVC 패턴

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