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    • 7. 서블릿 API 사용하기
      개발자 수업/JSP 2021. 11. 27. 21:27

      1. 서블릿 포워드 기능
          1) 하나의 서블릿에서 다른 서블릿 혹은 JSP와 연동하는 방법

      2. 포워드 기능의 용도
          1) 요청(request)에 대한 추가 작업을 다른 서블릿에게 수행하게 함
          2) 요청(request)에 포함된 정보를 다른 서블릿 혹은 JSP와 공유함
          3) 요청(request)에 정보를 포함시켜 다른 서블릿에 전달할 수 있음

      3. 서블릿 포워드 방법
          1) redirect를 이용한 포워딩
              - HttpServletResponse 객체의 sendRedirect() 메서드를 이용
              - 웹 브라우저에 재요청하는 방식
              - 형식 : sendRedirect("포워드할 서블릿 or JSP");

      package kr.co.ezenac.redirect;

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

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("/first")
public class FirstServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest reqeust, HttpServletResponse response) throws ServletException, IOException {
		
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		response.sendRedirect("second");	//웹 브라우저에게 다른 서블릿인 second로 재요청함
	}
}
      package kr.co.ezenac.redirect;

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

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("/second")
public class SecondServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		out.println("<html><body>");
		out.println("sendRedirect를 이용한 redirect 실행");
		out.println("</body></html>");
	}
}


          2) refresh 방법
              - HttpServletResponse 객체의 addHeader() 메서드를 이용
              - 웹 브라우저에 재요청하는 방식
              - 형식 : response.addHeader("Refresh", 경과시간(초);url=요청할 서블릿 or JSP);

      package kr.co.ezenac.redirect02;

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

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("/first2")
public class FirstServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest reqeust, HttpServletResponse response) throws ServletException, IOException {
		
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		response.addHeader("Refresh", "1;url=second2");	//웹 브라우저에게 1초 후 서블릿인 second2로 재요청함
	}
}
      package kr.co.ezenac.redirect02;

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

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("/second2")
public class SecondServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		out.println("<html><body>");
		out.println("refresh를 이용한 redirect 실행");
		out.println("</body></html>");
	}
}

          3) location 방법
              - 자바스크립트 location 객체의 href 속성을 이용
              - 자바스크립트에서 재요청하는 방식
              - 형식) location.href = '요청할 서블릿 or JSP';

      package kr.co.ezenac.location;

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

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("/first3")
public class FirstServlet extends HttpServlet{
	
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		out.print("<script type='text/javascript'>");
		out.print("location.href='second3';");
		out.print("</script>");
	}
}
      package kr.co.ezenac.location;

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

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("/second3")
public class SecondServlet extends HttpServlet {
	
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		out.print("<html><body>");
		out.print("location을 이용한 redirect 테스트입니다.");
		out.print("</body></html>");
	}
}


          4) 위의 1~3 redirect 방식으로 다른 서블릿에 데이터 전달하기

      package kr.co.ezenac.redirectData;

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

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("/first4")
public class FirstServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		response.sendRedirect("second4?name=lee");	//Get 방식 이용해 이름/값 쌍으로 데이터를 다른 서블릿으로 전달함
	}
}
      package kr.co.ezenac.redirectData;

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

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("/second4")
public class SecondServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		String name = request.getParameter("name");		//name으로 이전 서블릿에서 전달된 lee를 받음
		
		out.println("<html><body>");
		out.print("이름 : " + name);
		out.print("<br>");
		out.println("</body></html>");
	}
}


          5) dispatch 방법
              - 일반적으로 포워딩 기능을 지칭
              - 서블릿이 직접 요청하는 방법
              - RequestDispatcher 클래스의 forward() 메서드 이용
              - 형식) RequestDispatcher dis = request.getRequestDispatcher("포워드 할 서블릿 or JSP");
                      dis.forward(request, responce);
              - 모델2나 스프링 프레임워크에서 포워딩시 사용
              - 웹 브라우저 주소 창의 URL이 변경되지 않고 그대로임
                  - 서블릿의 포워드가 서버에서 수행되었기 때문임

      package kr.co.ezenac.dispatch;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
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("/first5")
public class FirstServlet extends HttpServlet {
	
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		
		//dispatcher 방법을 이용해 second로 전달함
		RequestDispatcher dispatcher = request.getRequestDispatcher("second5?name=lee2");
		dispatcher.forward(request, response);
	}
}
      package kr.co.ezenac.dispatch;

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

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("/second5")
public class SecondServlet extends HttpServlet{
	
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		String name = request.getParameter("name");		//다른 서블릿에서 전달된 데이터를 가져옴
		out.println("<html><body>");
		out.println("이름 : " + name);
		out.println("<br>");
		out.println("dispatch를 이용한 forward 테스트입니다.");
		out.println("</body></html>");
	}
}

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