Forwarding

서블릿 또는 JSP에서 요청을 받은 후에 다른 component로 요청을 위임할 수 있다. 그것을 포워딩이라한다.

포워딩 방법에는 2개의 클래스(RequestDispatcher, HttpServletResponse)를 이용한다.

RequestDispatcher 클래스

요청받은 요청객체(request)를 위임받는 컴포넌트(S2)에 동일하게 전달할 수 있다.

예제

dispatcher.jsp

<%@ page language="java" contentType="text/html; charset=EUC-KR"
    pageEncoding="EUC-KR"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>Insert title here</title>
</head>
<body>

        dispacherJsp.jsp
        <hr />

        id : <%= request.getAttribute("id") %> <br />
        pw : <%= request.getAttribute("pw") %>

</body>
</html>

RequestObj.java

package com.javalec.ex;

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;

/**
 * Servlet implementation class RequestObj
 */
@WebServlet("/RequestObj")
public class RequestObj extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public RequestObj() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("doGet");
        actionDo(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("doPost");
        actionDo(request, response);
    }

    private void actionDo(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("actionDo");

        request.setAttribute("id", "abcde");
        request.setAttribute("pw", "12345");

        RequestDispatcher dispatcher = request.getRequestDispatcher("/dispacherJsp.jsp");
        dispatcher.forward(request, response);

    }
}

RequestDispatcher dispatcher = request.getRequestDispatcher("/dispacherJsp.jsp");
dispatcher.forward(request, response);

클라이언트가 준 request객체에서 getRequestDispatcher("위임받을 컴포넌트") 로 생성해준다.

dispatcher.forward 로 전달해준다. 두 파일에서 사용하는 파일이 동일한 request라는 것을 확인할 수 있다.

HttpServletResponse 클래스

Request를 위임하는 클래스이다. 하지만 RequestDispatcher 클래스와의 차이점은 요청받은 객체를 위임 받는 컴포넌트에 전달하는 것이 아닌 새로운 객체를 생성한다.

예제

JSP

<%@ page language="java" contentType="text/html; charset=EUC-KR"
    pageEncoding="EUC-KR"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>Insert title here</title>
</head>
<body>

        <%
            request.setAttribute("id", "abcde");
            request.setAttribute("pw", "12345");

            response.sendRedirect("RequestObj");
        %>

</body>
</html>

response.sendRedirect("RequestObj"); 가 HttpServletResponse 객체이다.

RequestObj.java

package com.javalec.ex;

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

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;

/**
 * Servlet implementation class RequestObj
 */
@WebServlet("/RequestObj")
public class RequestObj extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public RequestObj() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("doGet");
        actionDo(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("doPost");
        actionDo(request, response);
    }

    private void actionDo(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("actionDo");

        String id = (String)request.getAttribute("id");
        String pw = (String)request.getAttribute("pw");

        response.setContentType("text/jhtml; charset=EUC-KR");
        PrintWriter writer = response.getWriter();
        writer.print("<html><head></head><body>");
        writer.print("RequestObj" + "<hr />");
        writer.print("id : " + id + "<br />");
        writer.print("pw : " + pw);
        writer.print("</body></html>");

    }
}

id: null
pw: null

null값이 뜨는 것을 볼 수 있다. 위임을 한다고 해서 바로 전달되는 것이 아니라 클라이언트가 다시 위임 받은 컴포넌트를 요청한다. 새로운 객체가 생성되어 전달되므로 요청받은 컴포넌트에 setAttribute 해준 값은 위임받은 Component로 전달되지 않는다.

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