Servlet

유병익·2022년 10월 17일

Spring springMVC

Spring MVC - 백엔드 웹 개발 핵심 기술

목록 보기

2/7

1. 프로젝트 생성

1.1 사전 준비물

프로젝트 선택
- Project: Gradle Project
- Spring Boot: 최신 버전 선택
- Language: Java
Project Metadata
- Group: hello
- Artifact: servlet
- Name: servlet
- Package name: hello.servlet
- Packaging: War (주의!)
- Java: 11
- Dependencies: Spring Web, Lombok

build.gradle 설정

plugins {
		id 'org.springframework.boot' version '2.4.3'
		id 'io.spring.dependency-management' version '1.0.11.RELEASE'
		id 'java'
		id 'war'
}
group = 'hello'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '11'
configurations {
		compileOnly {
				extendsFrom annotationProcessor
		}
}
repositories {
		mavenCentral()
}
dependencies {
		implementation 'org.springframework.boot:spring-boot-starter-web'
		compileOnly 'org.projectlombok:lombok'
		annotationProcessor 'org.projectlombok:lombok'
		providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'
		testImplementation 'org.springframework.boot:spring-boot-starter-test'
}
test {
		useJUnitPlatform()
}

2. HttpServletRequest

2.1 역할

Servlet은 개발자 대신 HTTP 요청 메시지 파싱
그 결과를 HttpServletRequest 객체에 담아서 제공

💡 HttpServletRequest를 사용하면 HTTP 요청 메시지를 편리하게 조회할 수 있다!

참고

📌 HttpServletRequest, HttpServletResponse 기능에 대해서 깊이 있는 이해를 하려면 HTTP 스펙이 제공하는 요청, 응답 메시지 자체를 이해해야 한다.

2.2 사용법

package hello.servlet.basic.request;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

//http://localhost:8080/request-header?username=hello
@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);
				 response.getWriter().write("ok");
		 }
}

2.2.1 start-line 정보 조회

Code

//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.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();
}

Result

--- REQUEST-LINE - start ---
request.getMethod() = GET
request.getProtocal() = HTTP/1.1
request.getScheme() = http
request.getRequestURL() = http://localhost:8080/request-header
request.getRequestURI() = /request-header
request.getQueryString() = username=hello
request.isSecure() = false
--- REQUEST-LINE - end ---

Code

//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();
}

Result

--- Headers - start ---
host: localhost:8080
connection: keep-alive
cache-control: max-age=0
sec-ch-ua: "Chromium";v="88", "Google Chrome";v="88", ";Not A Brand";v="99"
sec-ch-ua-mobile: ?0
upgrade-insecure-requests: 1
user-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 11_2_0) AppleWebKit/537.36 
(KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36
accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/
webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
sec-fetch-site: none
sec-fetch-mode: navigatesec-fetch-user: ?1
sec-fetch-dest: document
accept-encoding: gzip, deflate, br
accept-language: ko,en-US;q=0.9,en;q=0.8,ko-KR;q=0.7
--- Headers - end ---

2.2.3 Header 편리한 조회

Code

//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();
}

Result

--- Header 편의 조회 start ---
[Host 편의 조회]
request.getServerName() = localhost
request.getServerPort() = 8080
[Accept-Language 편의 조회]
locale = ko
locale = en_US
locale = en
locale = ko_KR
request.getLocale() = ko
[cookie 편의 조회]
[Content 편의 조회]
request.getContentType() = null
request.getContentLength() = -1
request.getCharacterEncoding() = UTF-8
--- Header 편의 조회 end ---

2.2.4 기타 정보 조회

Code

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();
}

Result

--- 기타 조회 start ---
[Remote 정보]
request.getRemoteHost() = 0:0:0:0:0:0:0:1
request.getRemoteAddr() = 0:0:0:0:0:0:0:1
request.getRemotePort() = 54305
[Local 정보]
request.getLocalName() = localhost
request.getLocalAddr() = 0:0:0:0:0:0:0:1
request.getLocalPort() = 8080
--- 기타 조회 end ---

💡 지금까지 HttpServletRequest를 사용해서 HTTP Message의 start-line, header 정보 조회 방법을 학습했다. 이제 HTTP 요청 데이터를 어떻게 조회하는지 알아보자.

3. HTTP Request Data

📌 HTTP 요청 메시지를 통해 클라이언트에서 서버로 데이터를 전달하는 방법을 알아보자.

주로 다음 3가지 방법을 사용한다.

3.1 GET - Query Parameter

URL의 Query Parameter에 데이터를 포함해서 전달
- 예시) /url?username=hello&age=20
검색, 필터, 페이징 등에서 많이 사용하는 방식
Query Parameter 조회 Methods

//단일 파라미터 조회
String username = request.getParameter("username");

//파라미터 이름들 모두 조회
Enumeration<String> parameterNames = request.getParameterNames();

//파라미터를 Map 으로 조회 
Map<String, String[]> parameterMap = request.getParameterMap(); 

//복수 파라미터 조회
String[] usernames = request.getParameterValues("username");

❓ 파라미터 이름은 하나인데 값이 중복이면? ex) username=hello&username=kim

→ request.getParameterValues() 사용

📌중복일 때 request.getParameter() 사용

→ request.getParameterValues() 의 첫 번째 값 반환

3.2 POST - HTML Form

content-type: application/x-www-form-urlencoded
Message Body에 Query Parameter 형식으로 전달
- ex) username=hello&age=20
회원 가입, 상품 주문, HTML Form 사용
hello-form.html

<!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>

POST의 HTML Form을 전송하면 웹 브라우저는 다음 형식으로 HTTP 메시지를 만든다.

요청 URL: http://localhost:8080/request-param

content-type: application/x-www-form-urlencoded

message body: username=hello&age=20

application/x-www-form-urlencoded 형식 == GET의 Query Parameter 형식

Query Parameter 조회 Method를 그대로 사용하면 됨

request.getParameter() → 두 방식 구분 없이 조회 가능

📌 content-type은 HTTP Message Body의 데이터 형식을 지정한다.

GET URL Query Parameter 형식으로 데이터를 전달
- HTTP Message Body 사용 X
- content-type이 없다.
POST HTML Form 형식으로 데이터를 전달
- HTTP Message Body에 해당 데이터를 포함해서 보냄
- HTTP Message Body에 포함된 데이터가 어떤 형식인지 content-type 지정 필수
- Form으로 데이터를 전송하는 형식 = application/x-www-form-urlencoded

❗ HTTP Message Body 에 Form Data 형식으로 전송하는 것은 POST Method만 가능!!

3.3 HTTP Message Body

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

3.3.1 HTTP Request Data - API Message Body - 단순 텍스트

Code

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-bodystring")
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");
		 }
}

HTTP Request 전송

결과

messageBody = hello

📌 HTTP Message Body의 데이터를 InputStream을 사용해서 직접 읽을 수 있음

3.3.2 HTTP Request Data - API Message Body - JSON

Code

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;
/**
 * http://localhost:8080/request-body-json
 *
 * JSON 형식 전송
 * content-type: application/json
 * message body: {"username": "hello", "age": 20}
 *
 */
@WebServlet(name = "requestBodyJsonServlet", urlPatterns = "/request-bodyjson")
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");
		 }
}

HTTP Request 전송

결과

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

📌 참고

JSON 결과를 파싱해 자바 객체로 변환 → JSON 변환 라이브러리를 추가해서 사용
- ex)Jackson, Gson
Spring MVC를 선택하면 기본으로 Jackson 라이브러리(ObjectMapper)를 함께 제공

4. HttpServletResponse & HTTP Response Data

4.1 HttpServletResponse 역할

HTTP Response Message 생성
HTTP Response Code 지정
Header 생성
Body 생성
편의 기능 제공
- ex) Content-Type, Cookie, Redirect

4.2 HttpServletResponse 사용법

4.2.1 HTTP Response Data - 단순 텍스트

Code

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;
/**
 * http://localhost:8080/response-header
 *
 */
@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, mustrevalidate");
				 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 Method

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)
}

Cookie 편의 Method

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 Method

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");
}

4.2.2 HTTP Response Data - HTML

Code

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>");
		 }
}

📌 HTTP 응답으로 HTML을 반환할 때는 content-type을 text/html로 지정해야함!!

4.2.3 HTTP Response Data - JSON

Code

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;
/**
 * http://localhost:8080/response-json
 *
 */
@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);
		 }
}

📌 HTTP 응답으로 JSON을 반환할 때는 content-type을 application/json로 지정해야함!!

📌 Jackson Libarary의 objectMapper.writeValueAsString()

객체를 JSON 문자로 변경할 수 있음

유병익

Backend 개발자가 되고 싶은

이전 포스트

웹 애플리케이션 이해

다음 포스트

Servlet

Spring MVC - 백엔드 웹 개발 핵심 기술

1. 프로젝트 생성

1.1 사전 준비물

2. HttpServletRequest

2.1 역할

2.2 사용법

2.2.1 start-line 정보 조회

2.2.2 전체 Header 정보 조회

2.2.3 Header 편리한 조회

2.2.4 기타 정보 조회

3. HTTP Request Data

3.1 GET - Query Parameter

3.2 POST - HTML Form

3.3 HTTP Message Body

3.3.1 HTTP Request Data - API Message Body - 단순 텍스트

3.3.2 HTTP Request Data - API Message Body - JSON

4. HttpServletResponse & HTTP Response Data

4.1 HttpServletResponse 역할

4.2 HttpServletResponse 사용법

4.2.1 HTTP Response Data - 단순 텍스트

4.2.2 HTTP Response Data - HTML

4.2.3 HTTP Response Data - JSON

웹 애플리케이션 이해

Servlet, JSP, MVC 패턴

0개의 댓글

관련 채용 정보