4. MVC 프레임워크 만들기(1)

프론트 컨트롤러 패턴 소개
프론트 컨트롤러 도입 - v1
View 분리 - v2

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프론트 컨트롤러 패턴 소개

프론트 컨트롤러 도입 전

프론트 컨트롤러 도입 후

 

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 됨

스프링 웹 MVC와 프론트 컨트롤러
스프링 웹 MVC의 핵심도 바로 FrontController
스프링 웹 MVC의 DispatcherServlet이 FrontController 패턴으로 구현되어 있음

프론트 컨트롤러 도입 - v1

프론트 컨트롤러를 단계적으로 도입해보자.

이번 목표는 기존 코드를 최대한 유지하면서, 프론트 컨트롤러를 도입하는 것이다. 먼저 구조를 맞추어두

고 점진적으로 리펙터링 해보자.

V1 구조

ControllerV1

package hello.servlet.web.frontcontroller.v1;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.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 된

다. 프론트 컨트롤러는 이 인터페이스를 호출해서 구현과 관계없이 로직의 일관성을 가져갈 수 있다.

이제 이 인터페이스를 구현한 컨트롤러를 만들어보자. 지금 단계에서는 기존 로직을 최대한 유지하는게 핵심

이다.
 

MemberFormControllerV1 - 회원 등록 컨트롤러

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

import hello.servlet.web.frontcontroller.v1.ControllerV1;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.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);
    }
}

 

MemberSaveControllerV1 - 회원 저장 컨트롤러

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

import hello.servlet.domain.member.Member;
import hello.servlet.domain.member.MemberRepository;
import hello.servlet.web.frontcontroller.v1.ControllerV1;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.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);
    }
}

 

MemberListControllerV1 - 회원 목록 컨트롤러

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

import hello.servlet.domain.member.Member;
import hello.servlet.domain.member.MemberRepository;
import hello.servlet.web.frontcontroller.v1.ControllerV1;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.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);
    }
}

 

내부 로직은 기존 서블릿과 거의 같다. 이제 프론트 컨트롤러를 만들어보자.

 

FrontControllerServletV1 - 프론트 컨트롤러

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 javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.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);
    }
}

 

프론트 컨트롤러 분석

urlPatterns
urlPatterns = "/front-controller/v1/*" :  /front-controller/v1 를 포함한 하위 모든 요청은 이 서블릿에서 받아들인다.

예) front-controller/v1, front-controller/v1/a, front-controller/v1/a/b

 

controllerMap

key: 매핑 URL

value: 호출될 컨트롤러

 

service()
먼저  requestURI 를 조회해서 실제 호출할 컨트롤러를  controllerMap 에서 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.

실행
등록: http://localhost:8080/front-controller/v1/members/new-form

저장: http://localhost:8080/front-controller/v1/members/save

목록:  http://localhost:8080/front-controller/v1/members

기존 서블릿, JSP로 만든 MVC와 동일하게 실행 되는 것을 확인할 수 있다.

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);

 

이 부분을 깔끔하게 분리하기 위해 별도로 뷰를 처리하는 객체를 만들자.

V2 구조

MyView

뷰 객체는 이후 다른 버전에서도 함께 사용하므로 패키지 위치를  frontcontroller 에 두었다

package hello.servlet.web.frontcontroller;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.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);
    }
}

 

이 코드만 봐서는 어떻게 활용하는지 아직 감이 안올 것이다. 다음 버전의 컨트롤러 인터페이스를 만들어보

자. 컨트롤러가 뷰를 반환하는 특징이 있다.

ControllerV2

package hello.servlet.web.frontcontroller.v2;

import hello.servlet.web.frontcontroller.MyView;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public interface ControllerV2 {

    MyView process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;
}

 

MemberFormControllerV2 - 회원 등록 폼

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

import hello.servlet.web.frontcontroller.MyView;
import hello.servlet.web.frontcontroller.v2.ControllerV2;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class MemberFormControllerV2 implements ControllerV2 {

    @Override
    public MyView process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        return new MyView("/WEB-INF/views/new-form.jsp");
    }
}

 

이제 각 컨트롤러는 복잡한  dispatcher.forward() 를 직접 생성해서 호출하지 않아도 된다. 

단순히 MyView 객체를 생성하고 거기에 뷰 이름만 넣고 반환하면 된다.

 ControllerV1 을 구현한 클래스와  ControllerV2 를 구현한 클래스를 비교해보면, 이 부분의 중복이 확실하

게 제거된 것을 확인할 수 있다.

MemberSaveControllerV2 - 회원 저장

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

import hello.servlet.domain.member.Member;
import hello.servlet.domain.member.MemberRepository;
import hello.servlet.web.frontcontroller.MyView;
import hello.servlet.web.frontcontroller.v2.ControllerV2;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.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");
    }
}

 

MemberListControllerV2 - 회원 목록

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

import hello.servlet.domain.member.Member;
import hello.servlet.domain.member.MemberRepository;
import hello.servlet.web.frontcontroller.MyView;
import hello.servlet.web.frontcontroller.v2.ControllerV2;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

public class MemberListControllerV2 implements ControllerV2 {

    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public MyView process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        List<Member> members = memberRepository.findAll();
        request.setAttribute("members", members);
        return new MyView("/WEB-INF/views/members.jsp");
    }

}

프론트 컨트롤러 V2

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 javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.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);
        view.render(request, response);
    }
}

 

ControllerV2의 반환 타입이  MyView 이므로 프론트 컨트롤러는 컨트롤러의 호출 결과로  MyView 를 반환
받는다. 그리고  view.render() 를 호출하면 로직을 수행해서 JSP가 실행된다.

MyView.render()

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

프론트 컨트롤러의 도입으로 MyView 객체의  render() 를 호출하는 부분을 모두 일관되게 처리할 수 있다. 각각의 컨트롤러는 MyView 객체를 생성만 해서 반환하면 된다.
 
실행
등록: http://localhost:8080/front-controller/v2/members/new-form

저장: http://localhost:8080/front-controller/v2/members/save

목록:  http://localhost:8080/front-controller/v2/members