基于myeclipse的用户登录

1、创建简单的用户登录界面（jsp文件），其中<select name="daylength">的功能是将用户登录后自动保存用户名及密码的时间，保证该用户再次登录时不需要输用户名及密码

<body>
    <div style="color:red;">${errmsg }</div>
  <form action="myservlet" method="post">
	    用户名：<input name="uname"> <br>
	    密码：<input type="password" name="upwd"> <br>
	    <select name="daylength">
	    	<option value="-1">请选择</option>
	    	<option value="3">3天</option>
	    	<option value="7">7天</option>
	    	<option value="30">30天</option>
	    </select>
	    <br>
	    <input type="submit" value="登录"> 
    </form>
  </body>

2、在index.jsp文件中获取cookie（通过cookie获取用户名及密码）

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
//获取全部cookie
Cookie[] cookies = request.getCookies();
String name = null,pwd = null;
//遍历
for(Cookie c : cookies){
	if(c.getName().equals("username")){
		//获取用户名
		name = c.getValue();
	}
	if(c.getName().equals("userpwd")){
		//获取密码
		pwd = c.getValue();
	}
}
if(name != null && pwd != null){
	//登录
	request.getRequestDispatcher("myservlet?uname="+name+"&upwd="+pwd).forward(request, response);
}
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

3、用户登录失败界面（用户登录失败将返回登录界面）

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

//判断session是否有用户名
String name = (String)session.getAttribute("currName");
if(name == null){
	//保存错误信息
	request.setAttribute("errmsg", "登录失败，请重新登录！");
	//非法访问，跳转回登录页面
	request.getRequestDispatcher("MyJsp.jsp").forward(request, response);
}
%>

4、用户登录成功的界面设定

（1）判断用户之前是否登陆过并作出相应判断

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

//判断session是否有用户名
String name = (String)session.getAttribute("currName");
if(name == null){
	//保存错误信息
	request.setAttribute("errmsg", "您还没有登录，请先登录！");
	//非法访问，跳转回登录页面
	request.getRequestDispatcher("MyJsp.jsp").forward(request, response);
}

%>

（2）用户登录成功后的显示并记录该用户是第几位登录，以及退出登录后返回到登录界面

 <body>
     欢迎！${currName }
    <br />
    您是第${count }位访问者。
    <br />
    <a href="outservlet">退出登录</a>
  </body>

5、用户信息的提取与保存（servlet）

package day01;

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

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

public class myservlet extends HttpServlet {

	public myservlet() {
		super(); 
		System.out.println("调用了构造方法");
	}
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		System.out.println("servlet成功销毁!");
	}
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//获取表单提交的数据
		String uname = request.getParameter("uname");
		String upwd = request.getParameter("upwd");
		if("lxd".equals(uname) && "123".equals(upwd)) {
			//获取是否保存用户名密码
			String daylength = request.getParameter("daylength");
			if(daylength != null && !daylength.equals("-1")){
				//保存
				int day = Integer.parseInt(daylength);
				Cookie cname = new Cookie("username", uname);
				Cookie cpwd = new Cookie("userpwd",upwd);
				//设置保存时间
				cname.setMaxAge(day*24*3600);
				cpwd.setMaxAge(day*24*3600);
				//添加到response
				response.addCookie(cname);
				response.addCookie(cpwd);
			}
			//将用户名保存在session中
			HttpSession session = request.getSession();
			session.setAttribute("currName", uname);
			//将用户名保存在request中
			request.setAttribute("abc", uname);
			//登录人数+1
			ServletContext sc = this.getServletContext();
			Integer count = (Integer)sc.getAttribute("count");
			if(count != null){
				count++;
			}else{
				count=1;
			}
			sc.setAttribute("count",count);
			//跳转到成功页面
            //response.sendRedirect("success.jsp");
			request.getRequestDispatcher("success.jsp").forward(request, response);
		}else{
			//跳转到失败页面
			response.sendRedirect("fail.jsp");
		}
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doGet(request, response);
	}
	public void init() throws ServletException {
		System.out.println("init()成功执行");
	}
}

6、退出登录并返回登录界面设定

package day01;

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 java.io.PrintWriter;

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

public class outservlet extends HttpServlet {
	public outservlet() {
		super();
	}
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//让session失效
		request.getSession().invalidate();
		response.sendRedirect("MyJsp.jsp");
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);
	}
}

7、执行效果

（1）登录界面

（2）用户登录失败

3）用户登录

！用户之前未登录时：

!!用户之前已经登录过时

（4）登录成功显示

（5）退出登录

基于myeclipse的用户登录

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