Spring MVC는 다른 많은 웹프레임워크와 마찬가지로 Front Controller Pattern와 Command Pattern을 사용합니다.

기본적인 Sevlet 구조

Servlet은 다음과 같은 web.xml 설정을 통해 요청과 Servlet이 1:1로 mapping 됩니다.

<servlet>
  <servlet-name>hello</servlet-name>
  <servlet-class>HelloServlet</servlet-class>
</servlet>
<servlet>
  <servlet-name>world</servlet-name>
  <servlet-class>WorldServlet</servlet-class>
</servlet>

<servlet-mapping>
  <servlet-name>hello</servlet-name>
  <url-pattern>/hello</url-pattern>
</servlet-mapping>
> <servlet-mapping>
  <servlet-name>world</servlet-name>
  <url-pattern>/world</url-pattern>
</servlet-mapping>

public class HelloServlet extends HttpServlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do GET http method - /hello");
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do POST http method - /hello");
  }
}

public class WorldServlet extends HttpServlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do GET http method - /world");
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do POST http method - /world");
  }
}

이러한 구조는 요청이 많아 질 수록 그만큼 Servlet도 많아져 복잡해집니다.

Front Controller Pattern

이러한 단점을 해결하고자 Front Controller Pattern이 등장하였습니다.
Front Controller을 해석하면 “앞에 있는 컨트롤”인 것처럼 모든 요청을 하나의 Servlet에서 받아 내부적으로 각 요청을 처리하는 형태입니다.

<servlet>
  <servlet-name>frontController</servlet-name>
  <servlet-class>FrontController</servlet-class>
</servlet>

<servlet-mapping>
  <servlet-name>frontController</servlet-name>
  <url-pattern>*.do</url-pattern>
</servlet-mapping>

public class FrontController extends HttpServlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      String url = request.getRequestURI().substring(request.contextPath.length());
      if(url.equals("/hello.do")) {
        System.out.println("Do GET http method - /http");
      } else if(url.equals("/world.do")) {
        System.out.println("Do GET http method - /world");
      }
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      String url = request.getRequestURI().substring(request.contextPath.length());
      if(url.equals("/hello.do")) {
        System.out.println("Do POST http method - /http");
      } else if(url.equals("/world.do")) {
        System.out.println("Do POST http method - /world");
      }
  }
}

FrontController 패턴은 모든 처리를 하나의 서블릿에서 처리하기 때문에 요청이 많아 질 수록 서블릿의 덩치가 커지게 됩니다.

Command Pattern

Command 패턴은 Interface를 구현한 클래스에 요청을 분산 시켜 관리하는 디자인 패턴입니다.

<servlet>
  <servlet-name>frontController</servlet-name>
  <servlet-class>FrontController</servlet-class>
</servlet>

<servlet-mapping>
  <servlet-name>frontController</servlet-name>
  <url-pattern>*.do</url-pattern>
</servlet-mapping>

public interface Controller extends HttpServlet {
}

public class HelloController extends HttpServlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do GET http method - /hello");
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do POST http method - /hello");
  }
}

public class WorldController extends HttpServlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do GET http method - /world");
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      System.out.println("Do POST http method - /world");
  }
}

public class FrontController extends HttpServlet {
  public HelloController helloController = new HelloController();
  public WorldController worldController = new WorldContoroller();
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      String url = request.getRequestURI().substring(request.contextPath.length());
      if(url.equals("/hello.do")) {
          helloController(request, response);
      } else if(url.equals("/world.do")) {
          worldController(request, response);
      }
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExceptionb, IOException {
      String url = request.getRequestURI().substring(request contextPath.length());
      if(url.equals("/hello.do")) {
          helloController(request, response);
      } else if(url.equals("/world.do")) {
          worldController(request, response);
      }
  }
}

이처럼 Spring MVC는 FrontControllerPattern과 CommandPattern을 적용하여 구현됩니다.