登录：
前端页面：
<body> ???<form action="/webtext/LogingServlet" method="post"> ???????<input type="text" name="username"><br> ???????<input type="text" name="userpassword"><br> ???????<input type="submit" value="登录"><br> ???</form></body>
domain：
public class user { ???private int uid; ???private String username; ???private String userpassword; ???public int getUid() { ???????return uid; ???} ???public void setUid(int uid) { ???????this.uid = uid; ???} ???public String getUsername() { ???????return username; ???} ???public void setUsername(String username) { ???????this.username = username; ???} ???public String getUserpassword() { ???????return userpassword; ???} ???public void setUserpassword(String userpassword) { ???????this.userpassword = userpassword; ???} ???@Override ???public String toString() { ???????return "user [uid=" + uid + ", username=" + username + ", userpassword=" + userpassword + "]"; ???}}dao层：
public int load(user user) throws SQLException{ ???Connection conn=JDBCUtils.getConn(); ???String sql="select * from user where username=? and userpassword=?"; ???PreparedStatement pst=conn.prepareStatement(sql); ???pst.setString(1, user.getUsername()); ???pst.setString(2, user.getUserpassword()); ???ResultSet rs = pst.executeQuery(); ???int count=0; ???while(rs.next()){ ???????count=rs.getInt(1); ???} ???JDBCUtils.close(rs, pst, conn); ???return count;}service层：
public boolean load(user user){ ???boolean flag=false; ???try { ???????int count=Dao.load(user); ???????if(count==1){ ???????????flag=true; ???????}else{ ???????????flag=false; ???????} ???} catch (SQLException e) { ???????// TODO Auto-generated catch block ???????e.printStackTrace(); ???} ???return flag;}登陆的同时检测登陆人数：
public class LogingServlet extends HttpServlet { ???private service Service=new service(); ???public void init() throws ServletException { ???????//获取ServletContext对象 ???????ServletContext servletContext=this.getServletContext(); ???????//向ServletContext域存入初始count ???????int count=0; ???????servletContext.setAttribute("count", count); ???????????} ???public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ???????String username=request.getParameter("username"); ???????String password=request.getParameter("userpassword"); ???????user user=new user(); ???????user.setUsername(username); ???????user.setUserpassword(password); ???????boolean flag=Service.load(user); ???????if(flag==true){ ???????????//获取ServletContext对象 ???????????ServletContext servletContext=this.getServletContext(); ???????????//获取当前count值 ???????????int count=(int)servletContext.getAttribute("count"); ???????????//改变count值 ???????????count++; ???????????response.getWriter().write("success"+user+"ni shi di"+count+"ge fang wen de ren"); ???????????//刷新count值 ???????????servletContext.setAttribute("count", count); ???????}else{ ???????????response.getWriter().write("failure"); ???????} ???} ???public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ???????doGet(request, response); ???}}注册：
dao层
//注册验证 ???public int zhuceyz(String username) throws SQLException{ ???????Connection conn=JDBCUtils.getConn(); ???????String sql="select username from user where username=?"; ???????PreparedStatement pst=conn.prepareStatement(sql); ???????pst.setString(1, username); ???????ResultSet rs = pst.executeQuery(); ???????int count=0; ???????while(rs.next()){ ???????????count=rs.getInt(1); ???????} ???????JDBCUtils.close(rs, pst, conn); ???????return count; ???} ???//存入注册信息 ???public int zhuce(user user) throws SQLException{ ???????Connection conn=JDBCUtils.getConn(); ???????String sql="insert into user(username,userpassword) values(?,?)"; ???????PreparedStatement pst=conn.prepareStatement(sql); ???????pst.setString(1, user.getUsername()); ???????pst.setString(2, user.getUserpassword()); ???????int row=pst.executeUpdate(); ???????JDBCUtils.close(pst, conn); ???????return row; ???}}service层
//注册验证 ???public boolean zhuceyz(String username){ ???????boolean flag=false; ???????try { ???????????int count=Dao.zhuceyz(username); ???????????if(count==0){ ???????????????flag=true; ???????????}else{ ???????????????flag=false; ???????????} ???????} catch (SQLException e) { ???????????// TODO Auto-generated catch block ???????????e.printStackTrace(); ???????} ???????return flag; ???} ???//存入注册信息 ???public boolean zhuce(user user){ ???????boolean flag=false; ???????try { ???????????int count=Dao.zhuce(user); ???????????if(count==1){ ???????????????flag=true; ???????????}else{ ???????????????flag=false; ???????????} ???????} catch (SQLException e) { ???????????// TODO Auto-generated catch block ???????????e.printStackTrace(); ???????} ???????return flag; ???}}服务器端
public class ZhuceServlet extends HttpServlet { ???private service Service=new service(); ???public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ???????while(true){ ???????????String username=request.getParameter("username"); ???????????String password=request.getParameter("userpassword"); ???????????boolean flag=Service.zhuceyz(username); ???????????if(flag==false){ ???????????????response.getWriter().write("yibeizhanyong"); ???????????????return; ???????????}else if(flag==true){ ???????????????user user=new user(); ???????????????user.setUsername(username); ???????????????user.setUserpassword(password); ???????????????boolean flag1=Service.zhuce(user); ???????????????if(flag==true){ ???????????????????response.getWriter().write("success"+user); ???????????????}else{ ???????????????????response.getWriter().write("failure"); ???????????????} ???????????} ???????????return; ???????} ???} ???public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ???????doGet(request, response); ???}}WEB简单的登录注册功能（分层）
原文地址：https://www.cnblogs.com/Ace-suiyuan008/p/9598413.html