What is Dispatcher-Servlet, Why & How to use

What is Dispatcher-Servlet: 

Dispatcher-Servlet is important in Spring MVC.

Dispatcher-Servlet first gets client's requests and sends them to corresponding controller.

Dispatcher-Servlet is called Front Controller.

 

 

 

Why use Dispatcher-Servlet : 

To process common codes in each controller.

To get all client requests using only a single dispatcher-servlet

Don't have to use servlet in other controllers except dispatcher-servlet

 

 

 

How to use Dispatcher-Servlet:

1. Make FrontControllerServletV1 class and extends HttpServlet.

@WebServlet(name = "frontControllerServletV1", urlPatterns = "/front-controller/v1/*")
public class FrontControllerServletV1 extends HttpServlet {

 

 

2. Make a Map. The Key is Strring and the value is a ControllerV1 Interface.

protected Map<String, ControllerV1> controllerMap = new HashMap<>();

 

 

3. Make a constructor consposed controllerMap.

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());
}

 

 

 

4. Search the controller from the url(location) mappring information.

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

    String requestURI = request.getRequestURI();

    ControllerV1 controller = controllerMap.get(requestURI);
    if(controller == null) {
        response.setStatus(HttpServletResponse.SC_NOT_FOUND);
        return;
    }

    controller.process(request, response);
}

 

 

getRequestURI() returns the part of this request's URL.    

 

 

Entire codes of FrontContollerServletV1 which is Dispatcher-Servlet.

@WebServlet(name = "frontControllerServletV1", urlPatterns = "/front-controller/v1/*")
public class FrontControllerServletV1 extends HttpServlet {

    protected 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 {

        String requestURI = request.getRequestURI();

        ControllerV1 controller = controllerMap.get(requestURI);
        if(controller == null) {
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        controller.process(request, response);
    }
}

 

 

 

Reference:

https://www.inflearn.com/course/%EC%8A%A4%ED%94%84%EB%A7%81-mvc-1/dashboard

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