4. MVC 프레임워크 만들기

프론트 컨트롤러 패턴

• 프론트 컨트롤러 서블릿 하나로 클라이언트 요청을 받는다.

• 이후 프론트 컨트롤러가 요청에 맞는 컨트롤러를 찾아서 호출한다.

• 입구가 하나이기 때문에 공통 부분을 프론트 컨트롤러에서 처리할 수 있다.

• 프론트 컨트롤러 이외의 다른 컨트롤러는 서블릿을 사용할 필요가 없다.

프론트 컨트롤러 도입 - v1

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

@WebServlet(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);
    }
}

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 데이터 보관
        request.setAttribute("member", member);

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

문제점

• view를 직접 호출하기 때문에 각 Controller에서 공통적인 부분이 존재하게 된다.

• Controller에서 view를 직접 알고 있어야 하기 때문에 view의 경로를 변경하려면 controller를 건드려야한다.

View 분리 - v2

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);
    }
}

public interface ControllerV2 {
    MyView process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;
}

@WebServlet(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 {
        System.out.println("FrontControllerServletV2.service");

        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);
    }
}

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 데이터 보관
        request.setAttribute("member", member);

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

문제점

• Controller입장에서 HttpServletRequest와 HttpServletResponse를 전혀 사용하지 않기 때문에 알 필요가 없다.
  • request.setAttribute()를 사용하고 있지만, 따로 Model 객체를 만들어서 전달하면 사용할 필요도 없다.

• 뷰 이름의 중복 부분(prefix, suffix)가 존재한다.

Model 추가 - v3

ModelView

• HttpSerlvetRequest에 데이터를 담지말고, 따로 ModelView객체를 만들어 Model정보 뿐만 아니라 View에 대한 정보도 모두 담을 수 있도록 한다.

@Getter
@Setter
public class ModelView {
    private String viewName;
    private Map<String, Object> model = new HashMap<>();

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

public class MyView {
		...
    public void render(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        modelToRequestAttribute(model, request);
        render(request, response);
    }

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

public interface ControllerV3 {
    ModelView process(Map<String, String> paramMap);
}

@WebServlet(urlPatterns = "/front-controller/v3/*")
public class FrontControllerServletV3 extends HttpServlet {
    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();
        ControllerV3 controller = controllerMap.get(requestURI);
        if (controller == null) {
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

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

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

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

    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;
    }
}

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);
        memberRepository.save(member);

        ModelView modelView = new ModelView("save-result");
        modelView.getModel().put("member", member);

        return modelView;
    }
}

문제점

• 여전히 Controller에서 계속 ModelView를 생성해서 반환해야한다. 여전히 중복적인 코드다.

단순하고 실용적인 컨트롤러 - v4

public interface ControllerV4 {
    String process(Map<String, String> paramMap, Map<String, Object> model);
}

@WebServlet(urlPatterns = "/front-controller/v4/*")
public class FrontControllerServletV4 extends HttpServlet {
    ...
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("FrontControllerServletV4.service");

        String requestURI = request.getRequestURI();
        ControllerV4 controller = controllerMap.get(requestURI);
        if (controller == null) {
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

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

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

        MyView view = viewResolver(viewName);
        view.render(model, request, response);
    }
		...
}

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);
        memberRepository.save(member);

        model.put("member", member);

        return "save-result";
    }
}

문제점

• 지금도 충분히 편리한 프레임워크이지만, 개발자가 V4컨트롤러 뿐만 아니라 V3나 V2, V1 컨트롤러도 사용하고 싶다면 지원할 수 있는 방법이 없다.

• 즉, 다른 형태의 컨트롤러를 지원할 수 있는 방법이 없다.

유연한 컨트롤러1 - v5(v3)

어댑터 패턴

• 진짜 우리가 아는 그 어댑터처럼, 이미 개발된 기존의 코드를 전혀 고치지 않고(V3, V4등) 코드의 인터페이스만 변경하여 활용하는 패턴이다.
  • V3 - ModelView process(Map<String, String> paramMap);
  • V4 - String process(Map<String, String> paramMap, Map<String, Object> model);

• 인터페이스가 다른 여러 컨트롤러(핸들러)를 호출하기 위해 어댑터를 정의하고, 각 어댑터를 호출하여 핸들러를 직접 핸들링 하도록 한다.

public interface MyHandlerAdapter {
    boolean supports(Object handler);

    ModelView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws ServletException, IOException;
}

public class ControllerV3HandlerAdapter implements MyHandlerAdapter {
    @Override
    public boolean supports(Object handler) {
        return handler instanceof ControllerV3;
    }

    @Override
    public ModelView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws ServletException, IOException {
        ControllerV3 controllerV3 = (ControllerV3) handler;

        Map<String, String> paramMap = createParamMap(request);
        return controllerV3.process(paramMap);
    }

    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;
    }
}

@WebServlet(urlPatterns = "/front-controller/v5/*")
public class FrontControllerServletV5 extends HttpServlet {
    private final Map<String, Object> handlerMappingMap = new HashMap<>();
    private final List<MyHandlerAdapter> handlerAdapters = new ArrayList<>();

    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());
		}

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

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        Object handler = getHandler(request);
        if (handler == null) {
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        MyHandlerAdapter adapter = getHandlerAdapter(handler);
        ModelView modelView = adapter.handle(request, response, handler);

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

    private MyHandlerAdapter getHandlerAdapter(Object handler) {
        return handlerAdapters.stream().filter(adapter -> adapter.supports(handler)).findFirst()
                .orElseThrow(() -> new IllegalArgumentException("handler adpater를 찾을 수 없습니다. handler = " + handler));
    }

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

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

유용한 컨트롤러2 - v5(v4)

• 이제 v5에 v4를 추가해보자.

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)
            throws ServletException, IOException {
        ControllerV4 controller = (ControllerV4) handler;

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

        String viewName = controller.process(paramMap, model);
        ModelView modelView = new ModelView(viewName);
        modelView.setModel(model);

        return modelView;
    }

    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;
    }
}

@WebServlet(urlPatterns = "/front-controller/v5/*")
public class FrontControllerServletV5 extends HttpServlet {
		...
    private void initHandlerMappingMap() {
        ...
        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 ControllerV4HandlerAdapter());
    }
		...
}

• FrontControllerServletV5에 적은 량의 코드만 추가하면 V4도 지원하는 FrontController를 만들 수 있다.

정리

• v1: 프론트 컨트롤러 도입
  • 기존 구조를 최대한 유지하면서 프론트 컨트롤러 도입

• v2: View 분류
  • 단순 반복되는 뷰 로직 관리

• v3: Model 추가
  • 서블릿 종속성 제거
  • 뷰 이름 중복 제거

• v4: 단순하고 실용적인 컨트롤러
  • v3와 거의 비슷
  • 구현 입장에서 ModelView를 직접 생성해서 반환하지 않도록 편리한 인터페이스 제공

• v5: 유연한 컨트롤러
  • 어댑터 도입
  • 어댑터를 추가해서 프레임워크를 유연하고 확장성 있게 설계

Uploaded by N2T

(23.06.21 22:15)에 작성된 글 입니다.