J2EE Design Patterns: Getting Started - View component and DTO
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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…
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