[스프링MVC - 1편] MVC 프레임워크 만들기 (1)

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 FrontController이다

스프링 웹 MVC의 DispatcherServlet이 FrontController 패턴으로 구현되어 있다

 

 

프론트 컨트롤러 도입 - v1

[V1 구조 ]

 

 

1. ControllerV1

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

서블릿과 비슷한 모양의 컨트롤러 인터페이스를 도입한다 (각 컨트롤러들은 이 인터페이스를 구현)

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

 

 

2. MemberFormControllerV1 - 회원 등록 컨트롤러

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);
    }
}

 

 

3. MemberSaveControllerV1 - 회원 저장 컨트롤러

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);

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

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

}

 

 

4. MemberListControllerV1 - 회원 목록 컨트롤러

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);
    }
}

 

 

5. FrontControllerServletV1 - 프론트 컨트롤러

@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/v1를 포함한 하위 모든 요청은 이 서블릿에서 받아들인다
• controllerMap
  • key : 매핑 URL
  • value : 호출될 컨트롤러
• service()
  • requestURI를 조회해서 실제 호출할 컨트롤러를 controllerMap에서 찾는다
  • 컨트롤러를 찾고 controller.process(request, response);을 호출해서 해당 컨트롤러를 실행한다
• JSP - 동일

 

 

View 분리 - v2

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

모든 컨트롤러에서 뷰로 이동하는 부분에 중복이 있고, 깔끔하지 않다

이 부분을 깔끔하게 분리하기 위해 별도로 뷰를 처리하는 객체를 만든다

 

 

V2 구조

 

 

1. MyView

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);
    }
}

 

 

2. ControllerV2

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

 

 

3. MemberFormControllerV2 - 회원 등록 폼

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");
    }
}

 

 

4. MemberSaveControllerV2 - 회원 저장

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);

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

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

 

 

5. MemberListControllerV2 - 회원 목록

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");
    }
}

 

 

6. 프론트 컨트롤러 V2

@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);
    }

}