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# 서블릿
## HttpServletResponse - 기본 사용방법
HttpServletResponse 역할
1. HTTP 응답 메시지 생성
- HTTP 응답코드 지정
- 헤더 생성
- 바디 생성
2. 편의 기능 제공
- Content-Type
- 쿠키
- Redirect
HttpServletResponse 기본 사용방법
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 = "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.setStatus(HttpServletResponse.SC_BAD_REQUEST);
// [response-header]
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"); // 직접 생성가능.
PrintWriter writer = response.getWriter();
writer.println("OK");
}
}
- Content 편의 메서드
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 = "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.setStatus(HttpServletResponse.SC_BAD_REQUEST);
// [response-header]
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"); // 직접 생성가능.
// [Header 편의 메서드]
content(response);
PrintWriter writer = response.getWriter();
writer.println("ok");
}
// [Header 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");
// response.setContentLength(2); //(생략시 자동 생성)
}
}
- 쿠키 편의 메서드
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.setStatus(HttpServletResponse.SC_BAD_REQUEST);
// [response-header]
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"); // 직접 생성가능.
// [Header 편의 메서드 - content]
// content(response);
// [Header 편의 메서드 - 쿠키]
cookie(response);
PrintWriter writer = response.getWriter();
writer.println("ok");
}
// [Header 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");
// response.setContentLength(2); //(생략시 자동 생성)
}
// [Header 편의 메서드 - 쿠키]
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 (GMT 기준)
response.addCookie(cookie);
}
}
- redirect 편의 메서드
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.setStatus(HttpServletResponse.SC_BAD_REQUEST);
// [response-header]
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"); // 직접 생성가능.
// [Header 편의 메서드 - content]
// content(response);
// [Header 편의 메서드 - 쿠키]
// cookie(response);
// [Header 편의 메서드 - redirect]
redirect(response);
PrintWriter writer = response.getWriter();
writer.println("ok");
}
// [Header 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");
// response.setContentLength(2); //(생략시 자동 생성)
}
// [Header 편의 메서드 - 쿠키]
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 (GMT 기준)
response.addCookie(cookie);
}
// [Header 편의 메서드 - redirect]
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
1. 단순 텍스트 응답
- ( writer.println("ok"); )
2. HTML 응답
3. HTTP API - MessageBody JSON 응답
HttpServletResponse - HTML 응답
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>HELLO 안녕</div>");
writer.println("</body>");
writer.println("</html>");
writer.close();
}
}
- HTTP 응답으로 HTML을 반환할 때는 content-type을 text/html 로 지정.
HTTP 응답 데이터 - API JSON
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 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(25);
// {"username" : "kim", "age" : 25}
String result = objectMapper.writeValueAsString(helloData);
response.getWriter().write(result);
}
}
- HTTP 응답으로 JSON을 반환할 때 content-type을 application/json 로 지정.
- Jackson 라이브러리가 제공하는 objectMapper.writeValueAsString() 를 사용 객체를 JSON 문자로 변경.
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