index.jsp

    

        用户名

        密码

        

    


check.jsp
// 导入驱动，加载具体驱动类
        Class.forName("com.mysql.cj.jdbc.Driver");
        // 与数据库建立连接
        connection = DriverManager.getConnection(URL, USERNAME, PSW);
        // 发送sql，执行增、删、改
        stmt = connection.createStatement();
        String name=request.getParameter("uname");
        String pwd=request.getParameter("upwd");

        //错误写法1：//String sql = "select count(*) from user where name=' "+name+" '  and  pwd=' "+pwd+" ' "; 

        String sql = "select count(*) from user where uname=' "+name+" '  and  upwd=' "+pwd+" ' ";
        //  =左边的uname是数据库中定义的字段名，右边的name是上面的String name获取的用户输入的值

        //错误写法2：//String sql = "select name,pwd from user where name='name'  and  pwd='pwd' ";