J2EE Design Patterns: Getting Started

The View component calls the controller component which in turn uses the DAO implementation to get the connection. Then it creates a DTO and passes it to the next View Component if the username and password are correct.

package loginmodule;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.*;
import javax.servlet.http.*;
import loginmodule.dao.LoginDAO;
import loginmodule.dto.LoginDTO;
public class Login extends HttpServlet {
    private static final String CONTENT_TYPE = "text/html; charset=windows-1252";
   private LoginDAO connection;   

   private ConfigService configService;
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
       try {
         connection=new DBConnection();
               }
       catch (Exception e) {
        e.printStackTrace();//for now just display the exception   
       }
    }
    public void doGet(HttpServletRequest request, 
                      HttpServletResponse response) throws ServletException,
IOException {response.setContentType(CONTENT_TYPE);
        PrintWriter out = response.getWriter();
        String flush=null;
        HttpSession session=request.getSession();       

       //implementation of the service class not shown for brevity
        service=new DataService(connection.getStatement());       

        String user=request.getParameter("user_txt");
        String passwd=request.getParameter("password_txt");       

//check user’s credential and if its ok create a dto and sent to the next
view
        if(isValidUser(user,passwd)) {           

//service class takes the user name, populates the dto and
returns //the dto
              session.setAttribute("USER",service.getDetails(user));
           

            RequestDispatcher dispatcher=request.getRequestDispatcher
(“/welcome.jsp”));
            dispactcher.forward(request,response);
        }
        else {
            flushSession(session);//invalidate the crated session on invalid
login
            RequestDispatcher dispactcher;
            dispactcher = request.getRequestDispatcher
(configService.getPage(ConfigService.PAGE_ERROR));
            dispactcher.forward(request,response);
        }       

        out.close();
    }
    public void doPost(HttpServletRequest request, 
                      HttpServletResponse response) throws ServletException,
IOException {
                          doGet(request,response);
                      }   

    private void flushSession(HttpSession session) {
        session.invalidate();
    }   

    public void destroy() {
    connection.close();       
    }
}

And here's the DTO.

package loginmodule.dto;
public class LoginDTO
{
  String user;
  String favColor; 

  public LoginDTO()
  {
  }
//the constructor called by service class to populate the dto
 public LoginDTO(String user, String favColor)
  {
    this.user=user;
    this.favColor=favColor;
  }
  public void setUser(String user)
  {
    this.user = user;
  }
  public String getUser()
  {
    return user;
  }
  public void setFavColor(String favColor)
  {
    this.favColor = favColor;
  }
  public String getFavColor()
  {
    return favColor;
  }
}

That’s it. In this part I have given a glimpse of what Design Patterns are and what can be achieved by implementing design patterns in context of J2EE. From the next part onwards I will focus on each Design Pattern available for each of the tiers. Till then…