16 - Mini MVC using Servlets: Page 3 of 3

f. Write displayRooms.jsp in WebContent directory.

<!DOCTYPE html>
<html>
<head>
<title>Available Rooms</title>
</head>
<%@ page import="java.util.List"%>
<%@ page import="java.util.ArrayList"%>
<%@ page import="com.servlet.tutorial.Room"%>
<body>
    <H4>Below Rooms are available for the selected Residence.</H4>
    <%
        Object obj  = request.getAttribute("availableRooms");
        List<Room> rooms = (List<Room>)obj;
    %>
    <table border="1">
        <thead>
            <tr>
                <th>Room Number</th>
                <th>Residence Code</th>
                <th>Floor Number</th>
                <th>Room Rent</th>
            </tr>
        </thead>
        <%
            for(int i=0;i<rooms.size();i++)
            {
                Room room = rooms.get(i);
        %>
        <tr>
            <td><%= room.getRoomNumber()%></td>
            <td><%= room.getResidenceCode()%></td>
            <td><%= room.getFloorNumber()%></td>
            <td><%= room.getRoomRent()%></td>
        </tr>
        <%      
            }
        %>     
    </table>                  
</body>
</html>

g. Write noRooms.jsp in WebContent directory.

<!DOCTYPE html>
<html>
<head>
<title>No Rooms</title>
</head>
<body>    
    <h4>Sorry There are no rooms available for the selected
        Residence!!</h4>
</body>
</html>

Testing

Hit http://localhost:8080/HelloWorld/SelectHostel.jsp and select any Residency other than Residence 4

Hit http://localhost:8080/HelloWorld/SelectHostel.jsp and select Residence 4

16.3 Alternate Approach.

Another approach to implement MVC is –

  1. Create a servlet which will just forward  request to some Controller say CommandController
  2. All JSP will send a hidden parameter in a request
  3. Controller will scan the hidden parameter and based on its value, invoke business classes. Based on result, returns the display name
  4. Servlet will read the result and forward the request to the returned display name.

Pseudo Code

  1. JSP will send hidden parameter say “Request_Type” and will post to say ActionServlet

<input type=”hidden” name=”Request_Type” value=”Login”/>

  1. ActionServlet will have following code in doPost()
String view = CommandController.processRequest(request,response);
RequestDispatcher rd = request.getRequestDispatcher(view);
    rd.forward(request,response);
  1. CommandController class will have one static method processRequest() like below
public static String processRequest(HttpServletRequest request, HttpServletResponse response )
{
    String requestType = request.getParameter(“Request_Type”);
    if(requestType.equals(“Login”)
    {
        // invoke corresponding business 
        return view;
    }
    else if(requestType.equals(“Logout”)
    {
        // invoke corresponding business 
        return view;
    }
}

Advantage of this approach is that your web application will have one and only Controller which is CommandController instead of all Servlets acting as a controller.

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