草草搞了个SERVLET的注册登陆功能

package cc.openhome.controller;

import java.io.*;
import java.util.*;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Register
 */
@WebServlet("/register.do")
public class Register extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private final String USERS = "C:/Users/sahara/workspace/Gossip/users";
    private final String SUCCESS_VIEW = "success.view";
    private final String ERROR_VIEW = "error.view";
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public Register() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().append("Served at: ").append(request.getContextPath());
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String email = request.getParameter("email");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String confirmedPasswd = 
                request.getParameter("confirmedPasswd");
        
        List<String> errors = new ArrayList<String>();
        if (isInvalidEmail(email)) {
            errors.add("no email or invalid email");
        }
        if (isInvalidUsername(username)) {
            errors.add("username is empty or has existed");
        }
        if (isInvalidPassword(password, confirmedPasswd)) {
            errors.add("please comfirm password again");
        }
        String resultPage = ERROR_VIEW;
        if(!errors.isEmpty()) {
            request.setAttribute("errors", errors);
        } else {
            resultPage = SUCCESS_VIEW;
            createUserData(email, username, password);
        }
        request.getRequestDispatcher(resultPage).forward(request, response);
        
    }
    
    private boolean isInvalidEmail(String email){
        return email == null||
                !email.matches("^[_a-z0-9-]+([.][_a-z0-9-]+)*@[_a-z0-9-]+([.][_a-z0-9-]+)*$");
    }
    
    private boolean isInvalidUsername(String username) {
        for (String file : new File(USERS).list()) {
            if (file.equals(username)) {
                return true;
            }
        }
        return false;
    }
    
    private boolean isInvalidPassword(String password,
            String comfirmedPasswd) {
        return false;
    }
    
    private void createUserData(String email, String username, String password) throws IOException {
        File userhome = new File(USERS + "/" + username);
        userhome.mkdir();
        BufferedWriter writer = new BufferedWriter(
                new FileWriter(userhome + "/profile"));
        writer.write(email + "\t" + password);
        writer.close();
    }

}