JDBC_基础的题库

JDBC

需求：

通过键盘录入用户名和密码

判断用户是否登录成功

select * from user where username = “” and password = “”;

如果这个sql有查询结果，则成功，反之，则失败

1. 步骤：

        1. 创建数据库表 user
            CREATE TABLE USER(
                id INT PRIMARY KEY AUTO_INCREMENT,
                username VARCHAR(32),
                PASSWORD VARCHAR(32)

            );

            INSERT INTO USER VALUES(NULL,'zhangsan','123');
            INSERT INTO USER VALUES(NULL,'lisi','234');

2. 代码：

            public class JDBCDemo {

                public static void main(String[] args) {
                    //1.键盘录入，接受用户名和密码
                    Scanner sc = new Scanner(System.in);
                    System.out.println("请输入用户名：");
                    String username = sc.nextLine();
                    System.out.println("请输入密码：");
                    String password = sc.nextLine();
                    //2.调用方法
                    boolean flag = new JDBCDemo9().login(username, password);
                    //3.判断结果，输出不同语句
                    if(flag){
                        //登录成功
                        System.out.println("登录成功！");
                    }else{
                        System.out.println("用户名或密码错误！");
                    }


                }



                /**
                 * 登录方法
                 */
                public boolean login(String username ,String password){
                    if(username == null || password == null){
                        return false;
                    }
                    //连接数据库判断是否登录成功
                    Connection conn = null;
                    Statement stmt =  null;
                    ResultSet rs = null;
                    //1.获取连接
                    try {
                        conn =  JDBCUtils.getConnection();
                        //2.定义sql
                        String sql = "select * from user where username = '"+username+"' and password = '"+password+"' ";
                        //3.获取执行sql的对象
                        stmt = conn.createStatement();
                        //4.执行查询
                        rs = stmt.executeQuery(sql);
                        //5.判断
                       /* if(rs.next()){//如果有下一行，则返回true
                            return true;
                        }else{
                            return false;
                        }*/
                       return rs.next();//如果有下一行，则返回true

                    } catch (SQLException e) {
                        e.printStackTrace();
                    }finally {
                        JDBCUtils.close(rs,stmt,conn);
                    }


                    return false;
                }
            }