[스프링 MVC 1편] #4. MVC 프레임워크 만들기 (1)

[Pracrobo]

MVC 프레임워크 만들기

프론트 컨트롤러 패턴 소개 - V1

FrontController 패턴 특징

• 프론트 컨트롤러 서블릿 하나로 클라이언트의 요청을 받음
• 프론트 컨트롤러가 요청에 맞는 컨트롤러를 찾아서 호출
• 입구를 하나로
• 공통 처리 가능
• 프론트 컨트롤러를 제외한 나머지 컨트롤러는 서블릿을 사용하지 않아도 된다.

"스프링 웹 MVC와 프론트 컨트롤러"

• 스프링 웹 MVC의 핵심도 바로 FrontController
• 스프링 웹 MVC의 "DispatcherServlet" 이 FrontController 패턴으로 구현되어 있음

프론트 컨트롤러의 도입 - V1

• 최대한 기존 코드를 유지하면서 프론트 컨트롤러를 도입하는 것
• 먼저 구조를 맞춰두고 점진적으로 리팩토링하기
  

package hello.servlet.web.frontcontroller.v1;

import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public interface ControllerV1 {
    void process (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;

}

• 서블릿과 비슷한 모양의 컨트롤러 인터페이스를 도입한다.
• 각 컨트롤러들은 이 인터페이스를 구현하면 된다.
• 프론트 컨트롤러는 이 인터페이스를 호출해서 구현과 관계없이 로직의 일관성을 가져갈 수 있다.

회원 등록 컨트롤러 V1(MemberFormControllerV1)

package hello.servlet.web.frontcontroller.v1.controller;

import hello.servlet.web.frontcontroller.v1.ControllerV1;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class MemberFormControllerV1 implements ControllerV1 {
    @Override
    public void process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String viewPath = "/WEB-INF/views/new-form.jsp";
        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
        dispatcher.forward(request, response);
    }
}

회원 저장 컨트롤러 V1(MemberSaveControllerV1)

package hello.servlet.web.frontcontroller.v1.controller;

import hello.servlet.domain.Member;
import hello.servlet.domain.MemberRepository;
import hello.servlet.web.frontcontroller.v1.ControllerV1;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class MemberSaveControllerV1 implements ControllerV1 {

    private MemberRepository memberRepository = MemberRepository.getInstance();
    @Override
    public void process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        int age = Integer.parseInt(request.getParameter("age"));


        Member member = new Member(username, age);
        memberRepository.save(member);

        // Model에 데이터를 보관한다.
        request.setAttribute("member" , member);
        String viewPath = "/WEB-INF/views/save-result.jsp";
        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
        dispatcher.forward(request, response);
    }
}

회원 목록 컨트롤러 V1(MemberListControllerV1)

package hello.servlet.web.frontcontroller.v1.controller;

import hello.servlet.domain.Member;
import hello.servlet.domain.MemberRepository;
import hello.servlet.web.frontcontroller.v1.ControllerV1;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.List;

public class MemberListControllerV1 implements ControllerV1 {

    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public void process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Member> members = memberRepository.findAll();
        request.setAttribute("members", members);

        String viewPath = "/WEB-INF/views/members.jsp";
        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
        dispatcher.forward(request, response);

    }
}

package hello.servlet.web.frontcontroller.v1;

import hello.servlet.web.frontcontroller.v1.controller.MemberFormControllerV1;
import hello.servlet.web.frontcontroller.v1.controller.MemberListControllerV1;
import hello.servlet.web.frontcontroller.v1.controller.MemberSaveControllerV1;
import hello.servlet.web.servlet.MemberSaveServlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

@WebServlet(name = "FrontControllerServletV1", urlPatterns = "/front-controller/v1/*")
public class FrontControllerServletV1 extends HttpServlet {

    private Map<String, ControllerV1> controllerMap = new HashMap<>();

    public FrontControllerServletV1() {
        controllerMap.put("/front-controller/v1/members/new-form", new MemberFormControllerV1());
        controllerMap.put("/front-controller/v1/members/save", new MemberSaveControllerV1());
        controllerMap.put("/front-controller/v1/members", new MemberListControllerV1());

    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("FrontControllerServletV1.service");

    }
}

결과

FrontControllerServletV1

package hello.servlet.web.frontcontroller.v1;

import hello.servlet.web.frontcontroller.v1.controller.MemberFormControllerV1;
import hello.servlet.web.frontcontroller.v1.controller.MemberListControllerV1;
import hello.servlet.web.frontcontroller.v1.controller.MemberSaveControllerV1;
import hello.servlet.web.servlet.MemberSaveServlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

@WebServlet(name = "FrontControllerServletV1", urlPatterns = "/front-controller/v1/*")
public class FrontControllerServletV1 extends HttpServlet {

    private Map<String, ControllerV1> controllerMap = new HashMap<>();

    public FrontControllerServletV1() {
        controllerMap.put("/front-controller/v1/members/new-form", new MemberFormControllerV1());
        controllerMap.put("/front-controller/v1/members/save", new MemberSaveControllerV1());
        controllerMap.put("/front-controller/v1/members", new MemberListControllerV1());

    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("FrontControllerServletV1.service");
        String requestURI = request.getRequestURI();
        ControllerV1 controller = controllerMap.get(requestURI);
        if(controller == null) {
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        controller.process(request, response);
    }
}

결과

"흐름정리"

@WebServlet(name = "FrontControllerServletV1", urlPatterns = "/front-controller/v1/*")
public class FrontControllerServletV1 extends HttpServlet {

    private Map<String, ControllerV1> controllerMap = new HashMap<>();

    public FrontControllerServletV1() {
        controllerMap.put("/front-controller/v1/members/new-form", new MemberFormControllerV1());
        controllerMap.put("/front-controller/v1/members/save", new MemberSaveControllerV1());
        controllerMap.put("/front-controller/v1/members", new MemberListControllerV1());

    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("FrontControllerServletV1.service");
        //front-controller/v1/members
        String requestURI = request.getRequestURI();
        // ControllerV1 controller =   MemberListControllerV1(); //다형성, 인스턴스 주소가 들어온다.
        ControllerV1 controller = controllerMap.get(requestURI);

        if(controller == null) {
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        controller.process(request, response); //@Override 호출
        
    }
}

"NotFound"

결과

프론트 컨트롤러 분석

urlPatterns

• urlPatterns = "/front-controller/v1/*" : /front-controller/v1를 포함한 하위 모든 요청은 이 서블릿에서 받아들인다.
• ex) /front-controller/v1, /front-controller/v1/a, /front-controller/v1/a/b

controllerMap

• key: 매핑 URL
• value: 호출될 컨트롤러

service()
먼저requestURI를 조회해서 실제 호출할 컨트롤러를 controllerMap에서 찾는다. 만약 없다면 404(SC_NOT_FOUND) 상태 코드를 반환한다.
컨트롤러를 찾고 controller.process(request, response);을 호출해서 해당 컨트롤러를 실행한다.

JSP
JSP는 이전 MVC에서 사용했던 것을 그대로 사용한다

View 분리 - V2

모든 컨트롤러에서 뷰로 이동하는 부분에 중복이 있고, 깔끔하지 않다.

String viewPath = "/WEB-INF/views/new-form.jsp";
RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
dispatcher.forward(request, response);

MyView 객체를 만들어 호출한다.

package hello.servlet.web.frontcontroller;

import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class MyView {
    private String viewPath;

    public MyView(String viewPath) {
        this.viewPath = viewPath;
    }

    public void render(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
        dispatcher.forward(request, response);
    }
}

view 분리 - MemberFormControllerV2

package hello.servlet.web.frontcontroller.v2.controller;

import hello.servlet.web.frontcontroller.MyView;
import hello.servlet.web.frontcontroller.v2.ControllerV2;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class MemberFormControllerV2 implements ControllerV2 {
    @Override
    public MyView process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //   MyView myView = new MyView("/WEB-INF/views/new-form.jsp");
        //   return myView; 
        // inline으로 합친다. Ctrl + Alt + Shift + T (refactoring)      
        return new MyView("/WEB-INF/views/new-form.jsp");
    }
}

view 분리 - MemberListControllerV2

package hello.servlet.web.frontcontroller.v1.controller;

import hello.servlet.domain.Member;
import hello.servlet.domain.MemberRepository;
import hello.servlet.web.frontcontroller.v1.ControllerV1;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.List;

public class MemberListControllerV1 implements ControllerV1 {

    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public void process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Member> members = memberRepository.findAll();
        request.setAttribute("members", members);

        String viewPath = "/WEB-INF/views/members.jsp";
        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
        dispatcher.forward(request, response);

    }
}

view 분리 - MemberSaveControllerV2

package hello.servlet.web.frontcontroller.v2.controller;

import hello.servlet.domain.Member;
import hello.servlet.domain.MemberRepository;
import hello.servlet.web.frontcontroller.MyView;
import hello.servlet.web.frontcontroller.v2.ControllerV2;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class MemberSaveControllerV2 implements ControllerV2 {
    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public MyView process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        int age = Integer.parseInt(request.getParameter("age"));


        Member member = new Member(username, age);
        memberRepository.save(member);

        // Model에 데이터를 보관한다.
        request.setAttribute("member" , member);

        return new MyView("/WEB-INF/views/save-result.jsp");
    }
}

FrontControllerServletV2

package hello.servlet.web.frontcontroller.v2;

import hello.servlet.web.frontcontroller.MyView;
import hello.servlet.web.frontcontroller.v2.controller.MemberFormControllerV2;
import hello.servlet.web.frontcontroller.v2.controller.MemberListControllerV2;
import hello.servlet.web.frontcontroller.v2.controller.MemberSaveControllerV2;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

@WebServlet(name = "FrontControllerServletV2", urlPatterns = "/front-controller/v2/*")
public class FrontControllerServletV2 extends HttpServlet {

    private Map<String, ControllerV2> controllerMap = new HashMap<>();

    public FrontControllerServletV2() {
        controllerMap.put("/front-controller/v2/members/new-form", new MemberFormControllerV2());
        controllerMap.put("/front-controller/v2/members/save", new MemberSaveControllerV2());
        controllerMap.put("/front-controller/v2/members", new MemberListControllerV2());

    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String requestURI = request.getRequestURI();

        ControllerV2 controller = controllerMap.get(requestURI);

        if(controller == null) {
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        MyView view = controller.process(request, response);//@Override 호출
        view.render(request, response);

    }
}

결과

흐름정리

• 10:50부터 ~

• new MyView("/WEB-INF/views/new-form.jsp")의 render 호출

• MyView Class 의 viewPath의 객체에 URL값이 들어가있음

• forward해서 웹브라우저로 내려감

Controller V2 class

MyView view = controller.process(request, response);
        view.render(request, response);

ControllerV2의 반환 타입이 MyView이므로 프론트 컨트롤러는 컨트롤러의 호출 결과로 Myview를 반환받는다. 그리고 view.render()를 호출하면 forward로직을 수행해서 JSP가 실행된다.

 public void render(HttpServletRequest request, HttpServletResponse response) 
throws ServletException, IOException {
 RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
    dispatcher.forward(request, response);
 }

프론트 컨트롤러의 도입으로 HyView객체의 render()를 호출하는 부분을 모두 일관되게 처리할 수 있다. 각각의 컨트롤러는 MyView 객체를 생성만 해서 반환하면 된다.

단축키

• Ctrl + Alt + Shift + T : refactoring this
• Ctrl + Alt + N : inline Variable
• Ctrl + Alt + V
• Ctrl + Alt + B : Navigate > Go to Implementation(s) (옵션으로 들어감)