servlet servlet context 상태 저장소

ServletContext를 통해 저장하고 싶은 value 값을 (key, value) 형태로 저장할 수 있다.

package com.newlec.web;

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

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

@WebServlet("/calc2")
public class Calc2 extends HttpServlet{
	@Override
	protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
		PrintWriter out = res.getWriter();
		res.setCharacterEncoding("UTF-8");
		res.setContentType("text/html; charset=UTF-8");
		ServletContext application = req.getServletContext();
		String v_ = req.getParameter("v");
		String op = req.getParameter("op");
		int v=0;
		if (!v_.equals("")) v = Integer.parseInt(v_);
		
		if (op.equals("=")) {
			int x = (Integer)application.getAttribute("value");
			int y = v;
			int result=0;
			String operator = (String)application.getAttribute("op");
			if (operator.equals("+")) result = x+y;
			else result = x-y;
			
			out.println("result is "+result);
		}
		else {
			application.setAttribute("value",v);
			application.setAttribute("op",op);
		}
	}
}