[스프링 MVC - 백엔드 웹 개발 핵심 기술] 04. MVC 프레임워크 만들기

1. FrontController 패턴

- 프론트 컨트롤러 서블릿 하나로 클라이언트의 요청을 받음

- 프론트 컨트롤러가 요청에 맞는 컨트롤러를 찾아서 호출

- 프론트 컨트롤러를 제외한 나머지 컨트롤러는 서블릿을 사용하지 않아도 됨

@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);

    }
}

 

2. 서블릿 종속성 제거, 중복 요소 제거

- 컨트롤러 입장에서 HttpServletRequest, HttpServletResponse은 필요없음

- 요청 파라미터 정보는 자바의 Map으로 대신 넘기도록 하면 컨트롤러가 서블릿 기술을 몰라도 동작할 수 있다.

- 프레임워크나 공통 기능이 수고로워야 사용하는 개발자가 편리해진다.

@WebServlet(name = "frontControllerServletV4", urlPatterns = "/front-controller/v4/*")
public class FrontControllerServletV4 extends HttpServlet {

    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 {

        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);
    }

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

    private static 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;
    }
}

 

3. 어댑터 패턴 (유연한 컨트롤러)

- 다양한 버전의 컨트롤러를 자유롭게 사용하고 싶을 때 사용하는 것이 어댑터 패턴이다.

- 프론트 컨트롤러가 다양한 방식의 컨트롤러를 처리할 수 있도록 해보자.

@WebServlet(name = "frontControllerServletV5", 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());
        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 {

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

        MyHandlerAdapter adapter = getHandlerAdapter(handler);

        ModelView mv = adapter.handle(request, response, handler);

        String viewName = mv.getViewName();
        MyView view = viewResolver(viewName);

        view.render(mv.getModel(), request, response);
    }

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

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