스프링 MVC 3일차_서블릿_2

# 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.