Servlet + response.sendredirect & request dispatcher

[Rishabh Shah]

Hello Everyone,

Happy new year all of you,



I am making one website. Its demo website. URL is http://onlinemedicineshopping.jelastic.com. I have completed only 10 %. Now, The thing is, When I make new user, and submit, it redirects on my login page. but, When I click on back button, It gives me following error.

Note : I have not put any client side validation yet.

SEVERE: Servlet.service() for servlet SimpleCaptcha threw exception
java.lang.IllegalStateException: Cannot create a session after the response has been committed
at org.apache.catalina.connector.Request.doGetSession(Request.java:2381)
at org.apache.catalina.connector.Request.getSession(Request.java:2098)
at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:833)
at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:844)
at nl.captcha.servlet.SimpleCaptchaServlet.doGet(SimpleCaptchaServlet.java:73)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)

I know why is it happening..I also show you my code of servlet.

package com.onlinemedicine.controller;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import nl.captcha.Captcha;

import com.onlinemedicine.Forms.UserForm;
import com.onlinemedicine.bean.User;
import com.onlinemedicine.dao.UserDao;

public class UserRegistration extends HttpServlet {
	private static final long serialVersionUID = 1L;

	public UserRegistration() {
		super();

	}

	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {

	}

	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		HttpSession session = request.getSession();
		try {
			String username = request.getParameter("username");
			String password = request.getParameter("password");
			String firstname = request.getParameter("firstname");
			String middlename = request.getParameter("middlename");
			String lastname = request.getParameter("lastname");
			String gender = request.getParameter("gender");
			String dob = request.getParameter("dob");
			String emailid = request.getParameter("emailid");
			String secQue = request.getParameter("securityQuestion");
			String secAns = request.getParameter("securityAnswer");
			String address1 = request.getParameter("adderss1");
			String address2 = request.getParameter("adderss2");
			String city = request.getParameter("city");
			String pincode = request.getParameter("pincode");
			String phoneno = request.getParameter("phoneno");
			String capcha1 = request.getParameter("capcha1");

			User user = new User();
//set the values

			UserForm usrform = new UserForm();
			user = usrform.setUsers(username, password, firstname, middlename,
					lastname, gender, dob, emailid, secQue, secAns, address1,
					address2, city, pincode, phoneno);

			Captcha capchaName = null;
//whether session is null or not..

			if (session != null) {

// retrieve capcha from server side

				capchaName = (Captcha) session.getAttribute(Captcha.NAME);
				request.setCharacterEncoding("UTF-8");

//first I compare capcha......if it correct then it goes inside...
				if (capchaName.isCorrect(capcha1)) {

//Its dao class...
					UserDao userDao = new UserDao();

					userDao.openReadOperation();

//this is method it checks whether username is exist or not..

					boolean userExist = userDao.checkUserName(user);
					userDao.closeOperation();
					if (userExist) {

						System.out.println("username is available !");

						response.sendRedirect("login.jsp");
						

					} 
else {

						session.setAttribute("UserExist",
								"User name is Already Exist !");
						session.setAttribute("User", user);
						response.sendRedirect("UserRegistration.jsp");

					}
				}

				else {

					session.setAttribute("WrongCapcha",
							"Please Enter Capcha Again !");
					session.setAttribute("User", user);
					response.sendRedirect("UserRegistration.jsp");
				}

			}
		} catch (Exception e) {
			e.printStackTrace();

		}

	}

}

As you can see above, I get all the parameters in request,

1) I check Capcha on this servlet class. and becuase of this capcha..I am getting this problem.
2) I have used only response.sendredirect only..and In remaining code, I have used just response.sendredirect..but, can anyone tell us, in real time application, when do I use sendredirect or requestdipatcher. some of programmers say you can also use only sendredirect..but, I still want to know, In which situation I should use... ?
3) If I get any exceptions or error from any servet, or any other class, how to handle it on jps page...

Please reply..and also tell me whether I have used logic correct or not..and give me suggetions.

If you don't get anything, please let me know...

Thanks

[Pete Nelson]

I think the most important distinction between HttpServletResponse.send*(...) methods and using a RequestDispatcher is that the former are all part of the HTTP communication between server & browser, where the RequestDispatcher is specific to internal communication within your application server.

When you call sendRedirect, an HTTP "Location:" header is added to the send buffer to be flushed to the client. You're using the HttpServletResponse interface to speak HTTP to the client browser. And then you're done talking to the browser!

I use the sendRedirect when the servlet cannot fulfill the request, for example when a login is required (redirect to login page), or required form data is missing (redirect back to form). Basically, I'm just sending back in HTTP "I can't help you, go HERE".

When you use a RequestDispatcher, you're passing the request & response objects back to your app server, and telling it to do further work in order to fulfill the request. The browser never sees any of these URIs where the request & response objects are being dispatched.

RequestDispatcher plays a major role in Front Controller Pattern or MVC. The majority of my servlets serve no content directly, but look at the incoming data, and then use a RequestDispatcher to dispatch the request (and response) onto the appropriate worker and/or JSP template.

[Rishabh Shah]

ok..thanks Pete Nelson