新建项目
打开IDEA，并新建一个Web项目
添加Tomcat服务器，并添加包依赖
创建数据库，数据表，并添加内内容
创建Servlet，进行登陆验证
作者使用的Mysql 5.6版本，并且部署于服务器，所以先要去网上下载JDBC驱动(下载地址,mysql数据库与JDBC版本对应查看地址)，下载zip包并导入项目(参考博客),接下来就是新建Servlet编写代码了
1 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
2 // 获得输入流
3 PrintWriter out = response.getWriter();
4 // 从请求对象中获得指定参数的值
5 String strName = request.getParameter("txtName");
6 String strPwd = request.getParameter("txtPwd");
7 //定义数据库操作所需对象
8 Connection conn=null;
9 Statement stmt;
10 ResultSet rs;
11 PreparedStatement psmt;
12 // 数据库链接需要的参数
13 String driver="com.mysql.jdbc.Driver";
14 String url = "jdbc:mysql://49.234.222.244:3306/J2EE";
15 String user = "root";
16 String pwd = "990130";
17 try {
18 Class.forName(driver);
19 conn = DriverManager.getConnection(url,user,pwd);
20 String sql = "select * from USER where username=? and pwd=?";
21 psmt = conn.prepareStatement(sql);
22 psmt.setString(1,strName);
23 psmt.setString(2,strPwd);
24 rs = psmt.executeQuery();
25 if(rs.next())
26 {
27 //设置cookie
28 Cookie cooUsername = new Cookie("username",strName);
29 cooUsername.setMaxAge(60*60*24*7);
30 response.addCookie(cooUsername);
31 Cookie cooPwd = new Cookie("pwd",strPwd);
32 cooPwd.setMaxAge(60*60*24*7);
33 response.addCookie(cooPwd);
34
35 HttpSession session = request.getSession(true);
36 session.setAttribute("username",strName);
37 session.setAttribute("pwd",strPwd);
38
39 String path = request.getContextPath();
40 String basepath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
41 String page = basepath+"/page/Online.jsp";
42 response.sendRedirect(page);
43 }
44 else
45 {
46 out.println("错误的用户名和密码！");
47 }
48 psmt.close();
49 } catch (ClassNotFoundException | SQLException e) {
50 e.printStackTrace();
51 }
52 }
LoginServlet
编写完代码一定要记得在web.xml中注册！！！
如果用户在登录时选择保存登录信息，30天内，用户无需登录
这个功能可以通过Cookie实现，需要Servlet，同时需要修改js文件，下面贴出主要代码
1 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
2 Cookie coo = new Cookie("username", "tom");//创建一个键值对的cookie对象
3 coo.setMaxAge(60*60*24*7);//设置cookie的生命周期
4 response.addCookie(coo);//添加到response中
5 }
SetCookie
1 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
2 Cookie coo[] = request.getCookies();//获取request中cookie集合
3
4 //循环遍历
5 for (Cookie co : coo) {
6 System.out.println(co.getName() + ":" + co.getValue());
7 response.getWriter().println(co.getValue());
8 }
9 }
GetCookie
1 function getCookie(cname){
2 var name = cname + "=";
3 var ca = document.cookie.split(';');
4 for(var i=0; i<ca.length; i++) {
5 var c = ca[i].trim();
6 if (c.indexOf(name)==0) { return c.substring(name.length,c.length); }
7 }
8 return "";
9 }
10 function checkCookie(){
11 var user=getCookie("username");
12 var uname=document.getElementById("input_user");
13 var pwd=getCookie("pwd");
14 var upwd=document.getElementById("input_password");
15
16
17 if (user!=""){
18 var uname=document.getElementById("input_user");
19 uname.value=user;
20 upwd=pwd;
21 }
22 }
JS
显示网站当前在线人数
这个功能可以通过Session实现，需要Servlet,这里采用了Listener+Session
1 private static int activeSessions = 0; //初始化在线人数
2 // Public constructor is required by servlet spec
3
4 public void sessionCreated(HttpSessionEvent se) {
5 activeSessions++;
6 }
7
8 public void sessionDestroyed(HttpSessionEvent se) {
9 if(activeSessions>0)
10 {
11 activeSessions--;
12 }
13 }
14 public static String getActiveSessions() {
15 return String.valueOf(activeSessions);
16 }
ListenerSession
同时JSP页面添加
<%@ page import="SessionOnline.ListenerSession" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<%
String name= (String)request.getSession().getAttribute("username");
String pwd=(String)request.getSession().getAttribute("pwd");
String nums = (String)ListenerSession.getActiveSessions();
%>
<h1>您好！</h1>
<p>用户名:<%=name%><br></p>
<p>密码:<%=pwd%><br></p>
<p>在线人数:<%=nums%></p>
登录时用户名为中文可能不能正常识别，解决该问题
这个功能需要使用Filter实现，新建一个Filter，并将其用web.xml注册
1 @WebFilter(filterName = "GBFilter")
2 public class GBFilter implements Filter {
3 public void destroy() {
4 }
5
6 public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
7 String encoding=req.getCharacterEncoding();//原来的编码
8 encoding="utf-8";//新编码
9 req.setCharacterEncoding(encoding);
10 resp.setContentType("text/html;charset="+encoding);
11 chain.doFilter(req, resp);
12 }
13
14 public void init(FilterConfig config) throws ServletException {
15
16 }
GbFilter
最后附上web.xml中代码以及运行结果图
1 <!-- 登陆验证的servlet--> 2 <servlet> 3 <servlet-name>LoginServlet</servlet-name> 4 <servlet-class>LoginServlet</servlet-class> 5 </servlet> 6 <servlet-mapping> 7 <servlet-name>LoginServlet</servlet-name> 8 <url-pattern>/login</url-pattern> 9 </servlet-mapping> 10 <!-- Cookie设置的Servlet--> 11 <servlet> 12 <servlet-name>GetCookie</servlet-name> 13 <servlet-class>GetCookie</servlet-class> 14 </servlet> 15 <servlet-mapping> 16 <servlet-name>GetCookie</servlet-name> 17 <url-pattern>/GetCookie</url-pattern> 18 </servlet-mapping> 19 20 <servlet> 21 <servlet-name>SetCookie</servlet-name> 22 <servlet-class>SetCookie</servlet-class> 23 </servlet> 24 <servlet-mapping> 25 <servlet-name>SetCookie</servlet-name> 26 <url-pattern>/SetCookie</url-pattern> 27 </servlet-mapping> 28 <!-- Session设置的Servlet--> 29 <servlet> 30 <servlet-name>GetSession</servlet-name> 31 <servlet-class>GetSession</servlet-class> 32 </servlet> 33 <servlet-mapping> 34 <servlet-name>GetSession</servlet-name> 35 <url-pattern>/GetSession</url-pattern> 36 </servlet-mapping> 37 <!-- 过滤器Filter设置--> 38 <filter> 39 <filter-name>GBFilter</filter-name>//定义名字 40 <filter-class>GBFilter</filter-class>//实现类 41 </filter> 42 <filter-mapping> 43 <filter-name>GBFilter</filter-name> 44 <url-pattern>/*</url-pattern> 45 <dispatcher>REQUEST</dispatcher> 46 <dispatcher>FORWARD</dispatcher> 47 </filter-mapping>web.xml