实用Servlet实现登陆验证

package com.news.servlet;

import java.io.IOException;
import java.io.PrintWriter;

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 com.news.dao.UserDao;
import com.news.dao.impl.UserDaoImpl;
import com.news.entity.User;

public class LoginServlet extends HttpServlet {

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		HttpSession session = request.getSession();
		PrintWriter out = response.getWriter();
		
		String rand = (String)session.getAttribute("rand");
		   
	   	String username = request.getParameter("username");
	   	String userpwd = request.getParameter("userpwd");
	   	String srand = request.getParameter("rand");
	   	
	   	if(!rand.equals(srand)){
	   		out.println("<script>alert('验证码错误！！');location.href");
	   		return;
	   	}
	   	
	   	UserDao userDao = new UserDaoImpl();
	   	
	   	boolean flag = userDao.checkLogin(username,userpwd);
	   	
	   	if(flag){
	   		User user = new User();
	   		user.setUsername(username);
	   		session.setAttribute("user",user);
	   		response.sendRedirect("index.jsp");
	   	}
	   	else{
	   		response.sendRedirect("login.jsp");
	   	}
		
	}

}