java中如何加载登录页面对登录信息进行数据库查询

1、在jsp中输入以下代码

<form action="TestLoginservlet" method="post">
<pre>
用户名:<input type='text' name='userName'>
密码:<input type='password' name='userPassword'>
<input type='submit' name='sub' value="登录">
</pre>
</form>

2、在TestLoginservlet中输入以下代码

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
                //进行编码修正
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");
        //1、获得用户的输入
        String uname = request.getParameter("userName");
        String pwd = request.getParameter("userPassword");
        //2、连接数据库查询
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mymarket?characterEncoding=utf-8","root","123456");
            Statement statement = connection.createStatement();
            String sql = "select * from mymarket where userName='"+uname+"' and userPassword='"+pwd+"'";
            ResultSet resultSet = statement.executeQuery(sql);
            //3、处理结果
            if(resultSet.next()) {
                response.getWriter().println("<script>alert('登录成功')</script>");
            }else {
                response.getWriter().println("用户名或密码出错");
            }
            resultSet.close();
            connection.close();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

3、由于sql注入有可能对安全性造成破坏，因此在sql语句中不直接使用用户名和密码字符串拼接的形式，而是采用以下方式

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //response.getWriter().append("Served at: ").append(request.getContextPath());
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");
        //1、获得用户的输入
        String uname = request.getParameter("userName");
        String pwd = request.getParameter("userPassword");
        //2、连接数据库查询
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/数据表名?characterEncoding=utf-8","数据库用户名","密码");
            //防止sql注入
            String sql = "select * from mymarket where userName=? and userPassword=?";
            //预定义语句命令对象
            PreparedStatement pstatement = connection.prepareStatement(sql);
            pstatement.setString(1,uname);
            pstatement.setString(2,pwd);
            ResultSet resultSet = pstatement.executeQuery();
            //3、处理结果
            if(resultSet.next()) {
                //response.getWriter().println("登录成功");
                response.getWriter().println("<script>alert('登录成功')</script>");
            }else {
                response.getWriter().println("用户名或密码出错");
            }
            resultSet.close();
            connection.close();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }