c. Define a class GetAvailableRoomsByResidence will be a business logic class which will have all the business logic to pull the available rooms. As I mentioned earlier, ideally this data should come from database but here in this example we will return some dummy data.

package com.servlet.tutorial;
import java.util.ArrayList;
import java.util.List;
public class GetAvailableRoomsByResidence {
    public static List<Room> getAvailableRoomsByResidence(String residenceCode)
    {
        List<Room> availableRooms = new ArrayList<Room>();
        if(residenceCode.equals("Residence 1"))
        {
            Room room = new Room();
            room.setFloorNumber( "2" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R001" );
            room.setRoomRent(200);
            availableRooms.add(room);
            room = new Room();
            room.setFloorNumber( "1" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R002" );
            room.setRoomRent(230);
            availableRooms.add(room);
            room = new Room();
            room.setFloorNumber( "4" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R003" );
            room.setRoomRent(400);
            availableRooms.add(room);
        }
        else if(residenceCode.equals("Residence 2"))
        {
            Room room = new Room();
            room.setFloorNumber( "1" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R011" );
            room.setRoomRent(240);
            availableRooms.add(room);      
            room = new Room();                                                        
            room.setFloorNumber( "11" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R022" );
            room.setRoomRent(330);
            availableRooms.add(room);
            room = new Room();
            room.setFloorNumber( "4" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R013" );
            room.setRoomRent(300);
            availableRooms.add(room);
        }
        else if(residenceCode.equals("Residence 3"))
        {
            Room room = new Room();
            room.setFloorNumber( "1" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R111" );
            room.setRoomRent(440);
            availableRooms.add(room);
            room = new Room();
            room.setFloorNumber( "21" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R222" );
            room.setRoomRent(340);
            availableRooms.add(room);
            room = new Room();
            room.setFloorNumber( "4" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R213" );
            room.setRoomRent(300);
            availableRooms.add(room);
            room = new Room();
            room.setFloorNumber( "5" );
            room.setResidenceCode( residenceCode );
            room.setRoomNumber( "R513" );
            room.setRoomRent(360);
            availableRooms.add(room);
        }
        else if(residenceCode.equals("Residence 4"))
        {
            // No Rooms available 
        }                                                                 
        return availableRooms;                                                                                                                      
    }
}

d. Define Entry of “GetRoomsByResidenceServlet”  in web.xml

<servlet>
<servlet-name>GetRoomsByResidenceServlet</servlet-name>
<servlet-class>com.servlet.tutorial.GetRoomsByResidenceServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>GetRoomsByResidenceServlet</servlet-name>
    <url-pattern>/GetRoomsByResidenceServlet</url-pattern>
</servlet-mapping>

e. Write Servlet “GetRoomsByResidenceServlet” Code. Calling of Business classes and delegate to different presentation based on business logic results are highlighted in below code

package com.servlet.tutorial;
import java.io.IOException;
import java.util.List;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class GetRoomsByResidenceServlet extends HttpServlet {
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
{
    String residenceCode= request.getParameter("Residence");
    // invoke Business logic 
    List<Room> availableRooms = GetAvailableRoomsByResidence.getAvailableRoomsByResidence(residenceCode);
    // store the result in requst 
    request.setAttribute("availableRooms", availableRooms);
    if(availableRooms.size()>0)
    {
        RequestDispatcher rd = request.getRequestDispatcher("displayRooms.jsp");
        rd.forward(request, response);
    }
    else
    {
        RequestDispatcher rd = request.getRequestDispatcher("noRooms.jsp");
        rd.forward(request, response);
    }
    }
}