[스프링 MVC 1편 - 백엔드 웹 개발 핵심 기술] 5. MVC 프레임워크 만들기

1. 프론트 컨트롤러(Front Controller) 패턴 소개

특징

• 프론트 컨트롤러 서블릿 하나로 클라이언트의 요청을 받음
• 프론트 컨트롤러가 요청에 맞는 컨트롤러를 찾아서 호출 (입구를 하나로!)
• 공통 처리가 가능하며, 나머지 컨트롤러는 서블릿을 사용하지 않아도 됨

2. 프론트 컨트롤러 도입 - v1 (구조 맞추기)

기존 로직을 최대한 유지하면서 프론트 컨트롤러만 도입하는 단계입니다.

ControllerV1 인터페이스

package com.example.spring_mvc_study1_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;
}

MemberFormControllerV1 - 회원 등록 폼

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.controller;

import com.example.spring_mvc_study1_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);
    }
}

MemberSaveControllerV1 - 회원 저장

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_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);
        System.out.println("member = " + member);
        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

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_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 {
        System.out.println("MvcMemberListServlet.service");
        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);
    }
}

FrontControllerServletV1

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v1;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.controller.MemberFormControllerV1;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.controller.MemberListControllerV1;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.controller.MemberSaveControllerV1;
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/*") // v1으로 들어오는 요청은 해당 controller가 먼저 받음
public class FrontControllerServletV1 extends HttpServlet {

    // String의 URL이 들어오면, 그에 맞는 Controller를 반환해주기 위함
    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(); // localhost8080 뒤의 URL을 받음 예시 -> /front-controller/v1/members/new-form

        // 다형성에 의해 자식 객체 new MemberFormControllerV1(), MemberSaveControllerV1(), MemberListControllerV1() 을 ControllerV1으로 받을 수 있음
        ControllerV1 controller = controllerMap.get(requestURI);

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

        controller.process(request, response);

    }
}

3. View 분리 - v2 (중복 제거)

모든 컨트롤러에서 중복되는 forward 로직을 별도의 MyView 객체로 분리합니다.

MyView 클래스

package com.example.spring_mvc_study1_servlet.web.frontcontroller;

import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;

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

public class MyView {
    private String viewPath; // 예시: /front-controller/v2/members/new-form

    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);
    }

    public void render(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException  {

        modelToRequestAttribute(model, request); // model의 값을 모두 꺼내서, request에 setAttribute(key, value)로 모두 넣어줌
        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
        dispatcher.forward(request, response);
    }

    private void modelToRequestAttribute(Map<String, Object> model, HttpServletRequest request) {
        model.forEach((key, value)-> request.setAttribute(key,value));
    }
}

ControllerV2 인터페이스

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v2;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public interface ControllerV2 {

    // v1에서의 void 타입이 아닌 Myview 타입으로 만듬 -> dispather를 생성해서, forward하는 과정을 MyView에서 render() 함수로 처리
    MyView process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;
}

MemberFormControllerV2 - 회원 등록 폼

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_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 {
//        String viewPath = "/WEB-INF/views/new-form.jsp";
//        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
//        dispatcher.forward(request, response);

        // 위의 주석의 내용을 MyView에서 처리함
        // MyView myView = new MyView("/WEB-INF/views/new-form.jsp");
        // return myView;
        return new MyView("/WEB-INF/views/new-form.jsp");
    }
}

MemberSaveControllerV2 - 회원 저장

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.ControllerV1;
import com.example.spring_mvc_study1_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);
        System.out.println("member = " + member);
        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);

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

MemberListControllerV2 - 회원 목록

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.ControllerV1;
import com.example.spring_mvc_study1_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;
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 {
        System.out.println("MvcMemberListServlet.service");
        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);

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

FrontControllerServletV2

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v2;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v1.ControllerV1;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller.MemberFormControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller.MemberListControllerV2;
import com.example.spring_mvc_study1_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/*") // v2으로 들어오는 요청은 해당 controller가 먼저 받음
public class FrontControllerServletV2 extends HttpServlet {

    // String의 URL이 들어오면, 그에 맞는 Controller를 반환해주기 위함
    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 {
        System.out.println("FrontControllerServletV2.service");

        String requestURI = request.getRequestURI(); // localhost8080 뒤의 URL을 받음 예시 -> /front-controller/v2/members/new-form

        // 다형성에 의해 자식 객체 new MemberFormControllerV2(), MemberSaveControllerV2(), MemberListControllerV2() 을 ControllerV2으로 받을 수 있음
        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);

    }
}

4. Model 추가 - v3 (서블릿 종속성 제거)

컨트롤러가 서블릿 기술을 몰라도 동작할 수 있도록 파라미터는 Map으로, 응답은 ModelView 객체로 처리합니다.

ModelView 클래스

package com.example.spring_mvc_study1_servlet.web.frontcontroller;

import lombok.Getter;
import lombok.Setter;

import java.util.HashMap;
import java.util.Map;

@Getter
@Setter
public class ModelView {
    private String viewName; // 논리 이름 -> "new-form"
    private Map<String, Object> model = new HashMap<>(); // 화면에 뿌릴 데이터(model)

    public ModelView(String viewName) {
        this.viewName = viewName;
    }

}

ControllerV3 인터페이스

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v3;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;

import java.util.Map;

public interface ControllerV3 {

    ModelView process(Map<String, String> paramMap);
}

MemberFormControllerV3

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.ControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.ControllerV3;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

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

public class MemberFormControllerV3 implements ControllerV3 {

    @Override
    public ModelView process(Map<String, String> paramMap){
//        String viewPath = "/WEB-INF/views/new-form.jsp";
//        RequestDispatcher dispatcher = request.getRequestDispatcher(viewPath);
//        dispatcher.forward(request, response);

//        return new MyView("/WEB-INF/views/new-form.jsp");
        return new ModelView("new-form");
    }
}

MemberSaveControllerV3

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.ControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.ControllerV3;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

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

public class MemberSaveControllerV3 implements ControllerV3 {
    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public ModelView process(Map<String, String> paramMap){
        String username = paramMap.get("username");
        int age = Integer.parseInt(paramMap.get("age"));

        Member member = new Member(username, age);
        System.out.println("member = " + member);
        memberRepository.save(member);

//        //Model에 데이터를 보관한다.
//        request.setAttribute("member", member);
        ModelView mv = new ModelView("save-result");
        mv.getModel().put("member", member);
        return mv;

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

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

MemberListControllerV3

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.ControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.ControllerV3;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

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

public class MemberListControllerV3 implements ControllerV3 {
    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public ModelView process(Map<String, String> paramMap){
        System.out.println("MvcMemberListServlet.service");
        List<Member> members = memberRepository.findAll();

        ModelView mv = new ModelView("members");
        mv.getModel().put("members", members);

        return mv;

//        request.setAttribute("members", members);

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

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

FrontControllerServletV3

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v3;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.ControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller.MemberFormControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller.MemberListControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v2.controller.MemberSaveControllerV2;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberFormControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberListControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberSaveControllerV3;
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 = "frontControllerServletV3", urlPatterns = "/front-controller/v3/*") // v3으로 들어오는 요청은 해당 controller가 먼저 받음
public class FrontControllerServletV3 extends HttpServlet {

    // String의 URL이 들어오면, 그에 맞는 Controller를 반환해주기 위함
    private Map<String, ControllerV3> controllerMap = new HashMap<>();

    public FrontControllerServletV3() {
        controllerMap.put("/front-controller/v3/members/new-form", new MemberFormControllerV3());
        controllerMap.put("/front-controller/v3/members/save", new MemberSaveControllerV3());
        controllerMap.put("/front-controller/v3/members", new MemberListControllerV3());
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("FrontControllerServletV3.service");

        String requestURI = request.getRequestURI(); // localhost8080 뒤의 URL을 받음 예시 -> /front-controller/v2/members/new-form

        // 다형성에 의해 자식 객체 new MemberFormControllerV2(), MemberSaveControllerV2(), MemberListControllerV2() 을 ControllerV2으로 받을 수 있음
        ControllerV3 controller = controllerMap.get(requestURI);

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

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

        Map<String, String> paramMap = createParamMap(request);
        ModelView mv = controller.process(paramMap);

        String viewName = mv.getViewName(); // 논리 이름 -> "new-form"
        MyView view = viewResolver(viewName); // "/WEB-INF/views/new-form.jsp" 처럼의 이름으로 변경
        view.render(mv.getModel(), request, response);
    }

    private Map<String, String> createParamMap(HttpServletRequest request) {
        Map<String, String> paramMap = new HashMap<>();
        request.getParameterNames().asIterator()
                .forEachRemaining(paramName -> paramMap.put(paramName, request.getParameter(paramName)));
        return paramMap;
    }

    private MyView viewResolver(String viewName) {
        return new MyView("/WEB-INF/views/" + viewName + ".jsp");
    }
}

5. 단순하고 실용적인 컨트롤러 - v4 (개발자 편의성)

개발자가 ModelView를 직접 생성하지 않고, 뷰 이름만 반환하도록 실용성을 높였습니다.

ControllerV4 인터페이스

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v4;

import java.util.Map;

public interface ControllerV4 {

    /**
     *
     * @param paramMap
     * @param model
     * @return viewName
     */
    String process(Map<String, String> paramMap, Map<String, Object> model);
}

MemberFormControllerV4

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.ControllerV4;

import java.util.Map;

public class MemberFormControllerV4 implements ControllerV4 {

    @Override
    public String process(Map<String, String> paramMap, Map<String, Object> model) {
        return "new-form";
    }
}

MemberSaveControllerV4

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.ControllerV4;

import java.util.Map;

public class MemberSaveControllerV4 implements ControllerV4 {
    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public String process(Map<String, String> paramMap, Map<String, Object> model) {
        String username = paramMap.get("username");
        int age = Integer.parseInt(paramMap.get("age"));

        Member member = new Member(username, age);
        System.out.println("member = " + member);
        memberRepository.save(member);

        model.put("member", member);
        return "save-result";
    }
}

MemberListControllerV4

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller;

import com.example.spring_mvc_study1_servlet.domain.Member.Member;
import com.example.spring_mvc_study1_servlet.domain.Member.MemberRepository;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.ControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.ControllerV4;

import java.util.List;
import java.util.Map;

public class MemberListControllerV4 implements ControllerV4 {
    private MemberRepository memberRepository = MemberRepository.getInstance();

    @Override
    public String process(Map<String, String> paramMap, Map<String, Object> model) {
        System.out.println("MvcMemberListServlet.service");
        List<Member> members = memberRepository.findAll();

        model.put("members", members);
        return "members";
    }
}

FrontControllerServletV4

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v4;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.ControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberFormControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberListControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberSaveControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller.MemberFormControllerV4;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller.MemberListControllerV4;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller.MemberSaveControllerV4;
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;
import java.util.Objects;

@WebServlet(name = "frontControllerServletV4", urlPatterns = "/front-controller/v4/*") // v4으로 들어오는 요청은 해당 controller가 먼저 받음
public class FrontControllerServletV4 extends HttpServlet {

    // String의 URL이 들어오면, 그에 맞는 Controller를 반환해주기 위함
    private Map<String, ControllerV4> controllerMap = new HashMap<>();

    public FrontControllerServletV4() {
        controllerMap.put("/front-controller/v4/members/new-form", new MemberFormControllerV4());
        controllerMap.put("/front-controller/v4/members/save", new MemberSaveControllerV4());
        controllerMap.put("/front-controller/v4/members", new MemberListControllerV4());
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("FrontControllerServletV4.service");

        String requestURI = request.getRequestURI(); // localhost8080 뒤의 URL을 받음 예시 -> /front-controller/v2/members/new-form

        // 다형성에 의해 자식 객체 new MemberFormControllerV2(), MemberSaveControllerV2(), MemberListControllerV2() 을 ControllerV2으로 받을 수 있음
        ControllerV4 controller = controllerMap.get(requestURI);

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

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

        Map<String, String> paramMap = createParamMap(request);
        Map<String, Object> model = new HashMap<>();
        String viewName = controller.process(paramMap, model); // 논리 이름 -> "new-form"

        MyView view = viewResolver(viewName); // "/WEB-INF/views/new-form.jsp" 처럼의 이름으로 변경
        view.render(model, request, response);
    }

    private Map<String, String> createParamMap(HttpServletRequest request) {
        Map<String, String> paramMap = new HashMap<>();
        request.getParameterNames().asIterator()
                .forEachRemaining(paramName -> paramMap.put(paramName, request.getParameter(paramName)));
        return paramMap;
    }

    private MyView viewResolver(String viewName) {
        return new MyView("/WEB-INF/views/" + viewName + ".jsp");
    }
}

6. 유연한 컨트롤러 - v5 (어댑터 패턴)

다양한 방식의 컨트롤러를 호출할 수 있도록 어댑터 패턴을 도입하여 유연성을 확보합니다.

MyHandlerAdapter 인터페이스

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v5;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public interface MyHandlerAdapter {
    boolean supports(Object handler); // handler는 컨트롤러를 의미 -> 어댑터가 해당 컨트롤러를 처리할 수 있는지 판단하는 메서드

    // 어댑터는 실제 컨트롤러를 호출하고, 그 결과로 ModelView를 반환
    // 실제 컨트롤러가 ModelView를 반환하지 못하면, 어댑터가 ModelView를 직접 생성해서라도 반환
    // 이전에는 프론트 컨트롤러가 실제 컨트롤러를 호출했지만 이제는 이 어댑터를 통해서 실제 컨트롤러가 호출
    ModelView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws ServletException, IOException;
}

ControllerV3HandlerAdapter

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v5.adapter;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.ControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v5.MyHandlerAdapter;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.util.HashMap;
import java.util.Map;

public class ControllerV3HandlerAdapter implements MyHandlerAdapter {

    @Override
    public boolean supports(Object handler) {
        return (handler instanceof ControllerV3); // ControllerV3로 구현된 handler가 넘어오게 되면 True를 반환
    }

    @Override
    public ModelView handle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        // 예시 : MemberFormControllerV3() 반환
        ControllerV3 controller = (ControllerV3) handler;

        Map<String, String> paramMap = createParamMap(request);
        ModelView mv = controller.process(paramMap);
        return mv;
    }

    private Map<String, String> createParamMap(HttpServletRequest request) {
        Map<String, String> paramMap = new HashMap<>();
        request.getParameterNames().asIterator()
                .forEachRemaining(paramName -> paramMap.put(paramName, request.getParameter(paramName)));
        return paramMap;
    }
}

ControllerV4HandlerAdapter

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v5.adapter;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.ControllerV4;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v5.MyHandlerAdapter;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.util.HashMap;
import java.util.Map;

public class ControllerV4HandlerAdapter implements MyHandlerAdapter {

    @Override
    public boolean supports(Object handler) {
        return (handler instanceof ControllerV4);
    }

    @Override
    public ModelView handle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        ControllerV4 controller = (ControllerV4) handler;

        Map<String, String> paramMap = createParamMap(request);
        HashMap<String, Object> model = new HashMap<>();

        String viewName = controller.process(paramMap, model);

        ModelView mv = new ModelView(viewName);
        mv.setModel(model);

        return mv;
    }

    private Map<String, String> createParamMap(HttpServletRequest request) {
        Map<String, String> paramMap = new HashMap<>();
        request.getParameterNames().asIterator()
                .forEachRemaining(paramName -> paramMap.put(paramName, request.getParameter(paramName)));
        return paramMap;
    }
}

FrontControllerServletV5

package com.example.spring_mvc_study1_servlet.web.frontcontroller.v5;

import com.example.spring_mvc_study1_servlet.web.frontcontroller.ModelView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.MyView;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberFormControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberListControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v3.controller.MemberSaveControllerV3;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller.MemberFormControllerV4;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller.MemberListControllerV4;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v4.controller.MemberSaveControllerV4;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v5.adapter.ControllerV3HandlerAdapter;
import com.example.spring_mvc_study1_servlet.web.frontcontroller.v5.adapter.ControllerV4HandlerAdapter;
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.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@WebServlet(name = "frontControllerServletV5", urlPatterns = "/front-controller/v5/*") // v4으로 들어오는 요청은 해당 controller가 먼저 받음
public class FrontControllerServletV5 extends HttpServlet {

    // String의 URL이 들어오면, 그에 맞는 Controller를 반환해주기 위함
    private final Map<String, Object> handlerMappingMap = new HashMap<>(); // v1,v2,v3... 등 다양한 타입이 들어가야 하기 때문에 Object 사용
    private final List<MyHandlerAdapter> handlerAdapters = new ArrayList<>(); // 여러개의 adapter 중에서 필요한 것을 사용

    public FrontControllerServletV5() {
        initHandlerMappingMap();
        initHandlerAdapters();
    }

    private void initHandlerMappingMap() {
        handlerMappingMap.put("/front-controller/v5/v3/members/new-form", new MemberFormControllerV3());
        handlerMappingMap.put("/front-controller/v5/v3/members/save", new MemberSaveControllerV3());
        handlerMappingMap.put("/front-controller/v5/v3/members", new MemberListControllerV3());

        // V4 추가
        handlerMappingMap.put("/front-controller/v5/v4/members/new-form", new MemberFormControllerV4());
        handlerMappingMap.put("/front-controller/v5/v4/members/save", new MemberSaveControllerV4());
        handlerMappingMap.put("/front-controller/v5/v4/members", new MemberListControllerV4());
    }

    private void initHandlerAdapters() {
        handlerAdapters.add(new ControllerV3HandlerAdapter());
        handlerAdapters.add(new ControllerV4HandlerAdapter());
    }

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

        // 예시 : MemberFormControllerV4() 반환
        Object handler = getHandler(request);

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

        // 예시 : ControllerV4HandlerAdapter 반환
        MyHandlerAdapter adapter = getHandlerAdapter(handler);
        ModelView mv = adapter.handle(request, response, handler);

        MyView view = viewResolver(mv.getViewName());
        view.render(mv.getModel(), request, response);
    }

    private Object getHandler(HttpServletRequest request) {
        String requestURI = request.getRequestURI();
        return handlerMappingMap.get(requestURI);
    }

    private MyHandlerAdapter getHandlerAdapter(Object handler) {
        
        for (MyHandlerAdapter adapter : handlerAdapters) {
            if (adapter.supports(handler)) {
                return adapter;
            }
        }

        throw new IllegalArgumentException("handler adapter를 찾을 수 없습니다. handler=" + handler);
    }

    private MyView viewResolver(String viewName) {
        return new MyView("/WEB-INF/views/" + viewName + ".jsp");
    }
}

7. 정리

• v1: 프론트 컨트롤러 도입 (입구 단일화)
• v2: View 분류 (MyView 도입)
• v3: Model 추가 (서블릿 종속성 제거, 논리 뷰 이름 사용)
• v4: 실용성 개선 (String 반환 타입 컨트롤러)
• v5: 어댑터 도입 (다형성과 어댑터로 유연한 확장성 설계)