1、创建登录界面login.jsp
1.1 样式代码：

<style>
    body,p,div,ul,li,h1,h2,h3,h4,h5,h6{
        margin:0;
        padding: 0;
    }
    body{
        background: #E9E9E9; 
    }
    #login{
        width: 400px;
        height: 250px;
        background: #FFF;
        margin:200px auto;
        position: relative;
    }
    #login h1{
        text-align:center;
        position:absolute;
        left:120px;
        top:-40px;
        font-size:21px;
    }
    #login form p{
        text-align: center;
    }
    #user{
        background:url(images/user.png) rgba(0,0,0,.1) no-repeat;
        width: 200px;
        height: 30px;
        border:solid #ccc 1px;
        border-radius: 3px;
        padding-left: 32px;
        margin-top: 50px;
        margin-bottom: 30px;
    }
    #pwd{
        background: url(images/pwd.png) rgba(0,0,0,.1) no-repeat;
        width: 200px;
        height: 30px;
        border:solid #ccc 1px;
        border-radius: 3px;
        padding-left: 32px;
        margin-bottom: 30px;
    }
    #submit{
        width: 232px;
        height: 30px;
        background: rgba(0,0,0,.1);
        border:solid #ccc 1px;
        border-radius: 3px;
    }
    #submit:hover{
        cursor: pointer;
        background:#D8D8D8;
    }
</style>

1.2、form表单以及cookie设置：

<%
Cookie[] cookie_arr=request.getCookies();
%>
<div id="login">
<h1>登录管理</h1>
<form action="LoginServlet" method="post" id="login_form">
    <p><input type="text" name="userName" id="user" value="<%
    if(cookie_arr!=null){
        for(Cookie cookie:cookie_arr){
            if(cookie.getName().equals("login_uname")){
                out.print(cookie.getValue());
            }
        }
    }
    %>" placeholder="用户名"></p>
    <p><input type="password" name="userPassword"  id="pwd" value="<%
    //判断是否有用户信息存入cookie,如果有则读取
    if(cookie_arr!=null)
        {
            for(Cookie cookie:cookie_arr){
                if(cookie.getName().equals("login_pwd")){
            out.print(cookie.getValue());
        }
    }
            }
    %>" placeholder="密码"></p>
    <p><input type="checkbox" value="check" name="check">记住密码</p>
    <p><input type="submit" id="submit" name="sub" value="登录"></p>
</form>
</div>

2、配置LoginServlet.servlet

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    request.setCharacterEncoding("UTF-8");
        //1、获得用户信息
    String userName=request.getParameter("userName");
    String userPassword=request.getParameter("userPassword");
        
        //2、从数据库获取信息    
        String sql="select * from login_reg where userName=? && userPassword=?";
        List<Object> paramList=new ArrayList<Object>();
        paramList.add(userName);
        paramList.add(userPassword);
        DbHelper dbHelper=new DbHelper(); 
        List<Map<String, Object>> list=  dbHelper.executeQuery(sql, paramList);
        if(list!=null && list.size()>0) {
            if(request.getParameter("check")!=null) {
                //4、如果客户选择了记住密码则将用户名和密码存入cookie中
                Cookie uname_cookie=new Cookie("login_uname", userName);
                Cookie pwd_cookie=new Cookie("login_pwd", userPassword);
                uname_cookie.setPath("/reg_login");
                pwd_cookie.setPath("/reg_login");
                uname_cookie.setMaxAge(15*24*3600);
                pwd_cookie.setMaxAge(15*24*3600);
                response.addCookie(uname_cookie);
                response.addCookie(pwd_cookie);
            }
            response.sendRedirect("main.jsp");
        }else {
            response.getWriter().println("用户名或密码出错");
        }
    }

效果如图：

login.jpg