Servlet / JSP #10 동적 페이지

underlier12·2020년 1월 25일
서블릿
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SERVLET&JSP

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10. 동적 페이지

서버에서 페이지 전환하기

기존에는 아래와 같이 요청한 것에 대해서만 응답을 했다면 이제 이를 Redirection을 통해 전환

image.png

image.png

코드 추가

Calc2.java

package com.newlecture.web;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
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 javax.servlet.http.HttpSession;

@WebServlet("/calc2")
public class Calc2 extends HttpServlet{
	@Override
	protected void service(HttpServletRequest request
			, HttpServletResponse response) 
					throws ServletException, IOException {
		// Application 저장소 선언
		ServletContext application = request.getServletContext();
		
		// Session 선언
		HttpSession session = request.getSession();
		
		// Cookie 선언
		Cookie[] cookies = request.getCookies();
		
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html; charset=UTF-8");
		
		PrintWriter out = response.getWriter();
		
		String value_ = request.getParameter("value");
		String op = request.getParameter("operator");
		
		int value = 0;
				
		if(!value_.equals("")) value = Integer.parseInt(value_);
		
		// 계산
		if(op.equals("=")) {

			int x = 0;
			
			for(Cookie c : cookies) {
				if(c.getName().equals("value")) {
					x = Integer.parseInt(c.getValue());
					break;
				}
			}
			
			int y = value;

			String operator = "";
			
			for(Cookie c : cookies) {
				if(c.getName().equals("op")) {
					operator = c.getValue();
					break;
				}
			}
			
			int result = 0;
			
			if(operator.equals("+")) {
				result = x + y;					
			} else {
				result = x - y;
			}
			
			response.getWriter().printf("결과 값 : %d\n", result);
			
		} else { // 값 저장	
			Cookie valueCookie = new Cookie("value", String.valueOf(value));
			Cookie opCookie = new Cookie("op", op);
			
			// path 설정
			valueCookie.setPath("/calc2");
			opCookie.setPath("/calc2");
			
			// maxAge 설정 - 24시간 유지
			valueCookie.setMaxAge(24 * 60 * 60);
			opCookie.setMaxAge(24 * 60 * 60);
			
			response.addCookie(valueCookie);
			response.addCookie(opCookie);
			
			// Redirection
			response.sendRedirect("calc2.html");
		}
	}
}

서버 페이지의 필요성

서버 페이지(동적 페이지)의 등장은 사용자의 입력을 실시간으로 웹 페이지에 반영할 필요에 의해 나타남

image.png

따라서 아래와 같이 html 대신 servlet을 통해 redirection하여 페이지를 동적으로 작업해 넘김

image.png

동적인 페이지 서블릿 작성

정적인 html 코드를 동적인 servlet으로 변환

Calc3.java

여기에서는 쿠키의 정보들을 불러와 페이지에 보여줄 수 있도록 준비

package com.newlecture.web;

import java.io.IOException;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
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;

@WebServlet("/calc3")
public class Calc3 extends HttpServlet{
	@Override
	protected void service(HttpServletRequest request
			, HttpServletResponse response) 
					throws ServletException, IOException {
		
		// Cookie 선언
		Cookie[] cookies = request.getCookies();
		
		String value = request.getParameter("value");
		String operator = request.getParameter("operator");
		String dot = request.getParameter("dot");
		
		String exp = "";
		
		if(cookies!=null) {
			for(Cookie c : cookies) {
				if(c.getName().equals("exp")) {
					exp = c.getValue();
					break;
				}
			}			
		}
		
		if(operator != null && operator.equals("=")) {
			ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
			try {
				exp = String.valueOf(engine.eval(exp));
			} catch (ScriptException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		} else {
			exp += (value == null) ? "" : value;
			exp += (operator == null) ? "" : operator;
			exp += (dot == null) ? "" : dot;			
		}
		
		Cookie expCookie = new Cookie("exp", exp);
		
		// Redirection
		response.addCookie(expCookie);
		response.sendRedirect("calcpage");
		
	}
}

CalcPage.java

여기서는 전달 된 내용을 바탕으로 html 문서로 작성하여 사용자에게 보여줌

package com.newlecture.web;

import java.io.IOException;
import java.io.PrintWriter;

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;

@WebServlet("/calcpage")
public class CalcPage extends HttpServlet{
	@Override
	protected void service(HttpServletRequest request
			, HttpServletResponse response) 
					throws ServletException, IOException {
		

		String exp = "0";
		Cookie[] cookies = request.getCookies();
		
		if(cookies!=null) {
			for(Cookie c : cookies) {
				if(c.getName().equals("exp")) {
					exp = c.getValue();
					break;
				}
			}			
		}
		
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html; charset=UTF-8");
		
		PrintWriter out = response.getWriter();
		
		out.write("<!DOCTYPE html>");
		out.write("<html>");
		out.write("<head>");
		out.write("<meta charset=\"UTF-8\">");
		out.write("<title>Calculation</title>");
		out.write("<style>");
		out.write("input{");
		out.write("width: 50px;");
		out.write("	height: 50px;");
		out.write("}");

		out.write(".output{");
		out.write("	height: 50px;");
		out.write("	background: #e9e9e9;");
		out.write("	font-size: 24px;");
		out.write("	font-weight: bold;");
		out.write("	text-align: right;");
		out.write("	padding: 0px 5px;");
		out.write("}");
		out.write("</style>");
		out.write("</head>");
		out.write("<body>");
		out.write("	<div>");
		out.write("		<form action=\"calc3\" method=\"post\">");
		out.write("			<table>");
		out.write("				<tr>");
		out.printf("					<td class=\"output\" colspan=\"4\">%s</td>", exp);
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"CE\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"C\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"<-\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"/\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"7\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"8\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"9\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"*\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"4\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"5\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"6\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"-\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"1\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"2\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"3\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"+\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"0\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"dot\" value=\".\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"=\"/></td>");
		out.write("				</tr>");
		out.write("			</table>");
		out.write("		</form>");
		out.write("	</div>");
		out.write("</body>");
		out.write("</html>");
		
	}
}

위와 같이 무분별한 write() 메소드 사용은 추후 JSP 등장의 이유가 됨

GET / POST 특화된 서비스 함수

필요에 따라 service 함수 없이 doGet(), doPost() 메소드를 오버라이드하여 사용 가능
각기 달리 작성하여 특화되게 활용

image.png

만약 doGet(), doPost() 를 사용하지 않고 URL 접근시 405 Error 발생(허용되지 않는 메소드)
--> 404 Error : URL 없음 405 Error : URL은 있으나 이를 처리할 메소드 없음

image.png

코드 구현

calcultor.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="calculator" method="get">
		<input type="submit" value="요청">
	</form>
</body>
</html>

method 를 get / post 바꿔가며 테스트

Calculator.java

package com.newlecture.web;

import java.io.IOException;

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

@WebServlet("/calculator")
public class Calculator extends HttpServlet{
//	@Override
//	protected void service(HttpServletRequest req
//			, HttpServletResponse res) 
//					throws ServletException, IOException {
//
//		// getMethod()를 통해 전달된 식별자는 대문자
//		if(req.getMethod().equals("GET")) {
//			System.out.println("GET Request");
//		} else if(req.getMethod().equals("POST")) {
//			System.out.println("POST Request");
//		}
//		
//		// 요청에 따른 doGet(), doPost() 메소드 반환
//		super.service(req, res);
//	}
	
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("doGET Call");
	}
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("doPOST Call");
	}
}

서블릿 합치기

계산기 프로그램 합치기

위에서 진행하였던 내용들을 토대로 계산기 프로그램을 하나의 서블릿으로 합침
GET 요청에 대해서는 /calcpage가 POST 요청에 대해서는 /calc3 로 연결 시킴

image.png

위와 같이 분할 시 쿠키에 대한 문제 발생(Redundancy)

코드 수정

doGet()에는 기존 CalcPage.java의 내용을 doPost()에는 기존 Calc3.java의 내용을 삽입

Calculator.java

package com.newlecture.web;

import java.io.IOException;
import java.io.PrintWriter;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
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;

@WebServlet("/calculator")
public class Calculator extends HttpServlet{	
	@Override
	protected void doGet(HttpServletRequest request
			, HttpServletResponse response) 
					throws ServletException, IOException {
		
		String exp = "0";
		Cookie[] cookies = request.getCookies();
		
		if(cookies!=null) {
			for(Cookie c : cookies) {
				if(c.getName().equals("exp")) {
					exp = c.getValue();
					break;
				}
			}			
		}
		
		response.setCharacterEncoding("UTF-8");
		response.setContentType("text/html; charset=UTF-8");
		
		PrintWriter out = response.getWriter();
		
		out.write("<!DOCTYPE html>");
		out.write("<html>");
		out.write("<head>");
		out.write("<meta charset=\"UTF-8\">");
		out.write("<title>Calculation</title>");
		out.write("<style>");
		out.write("input{");
		out.write("width: 50px;");
		out.write("	height: 50px;");
		out.write("}");

		out.write(".output{");
		out.write("	height: 50px;");
		out.write("	background: #e9e9e9;");
		out.write("	font-size: 24px;");
		out.write("	font-weight: bold;");
		out.write("	text-align: right;");
		out.write("	padding: 0px 5px;");
		out.write("}");
		out.write("</style>");
		out.write("</head>");
		out.write("<body>");
		out.write("	<div>");
		out.write("		<form method=\"post\">");
		out.write("			<table>");
		out.write("				<tr>");
		out.printf("					<td class=\"output\" colspan=\"4\">%s</td>", exp);
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"CE\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"C\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"<-\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"/\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"7\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"8\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"9\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"*\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"4\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"5\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"6\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"-\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"1\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"2\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"3\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"+\"/></td>");
		out.write("				</tr>");
		out.write("				<tr>");
		out.write("					<td></td>");
		out.write("					<td><input type=\"submit\" name=\"value\" value=\"0\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"dot\" value=\".\"/></td>");
		out.write("					<td><input type=\"submit\" name=\"operator\" value=\"=\"/></td>");
		out.write("				</tr>");
		out.write("			</table>");
		out.write("		</form>");
		out.write("	</div>");
		out.write("</body>");
		out.write("</html>");
	}
	
	@Override
	protected void doPost(HttpServletRequest request
			, HttpServletResponse response) 
					throws ServletException, IOException {
	
		// Cookie 선언
		Cookie[] cookies = request.getCookies();
		
		String value = request.getParameter("value");
		String operator = request.getParameter("operator");
		String dot = request.getParameter("dot");
		
		String exp = "";
		
		if(cookies!=null) {
			for(Cookie c : cookies) {
				if(c.getName().equals("exp")) {
					exp = c.getValue();
					break;
				}
			}			
		}
		
		if(operator != null && operator.equals("=")) {
			ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
			try {
				exp = String.valueOf(engine.eval(exp));
			} catch (ScriptException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		} else {
			exp += (value == null) ? "" : value;
			exp += (operator == null) ? "" : operator;
			exp += (dot == null) ? "" : dot;			
		}
		
		Cookie expCookie = new Cookie("exp", exp);
		
		// setMaxAge, setPath
		if(operator != null && operator.equals("C")) {
			expCookie.setMaxAge(0);
		}
		expCookie.setPath("/calculator");
		
		// Redirection
		response.addCookie(expCookie);
		response.sendRedirect("calculator");
	}
}
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Servlet / JSP #09 상태 유지를 위한 방법

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Servlet / JSP #11 JSP Program

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