登录案例

需求:

• 通过控制台用户输入用户名和密码。

• 用户输入的用户名和密码作为条件，编写查询 SQL 语句。

  • select * from user where username = xxx and password = xxx

• 如果该用户存在，提示登录成功，反之提示失败。

public class Demo_login {
​public static void main(String[] args) {Scanner scanner = new Scanner(System.in);System.out.println("请输入用户名:" );String username = scanner.nextLine( );
​System.out.println("请输入密  码:" );String password = scanner.nextLine( );
​boolean login = login(username, password);System.out.println(login );}
​// 设计方法,传入用户名和密码,返回是否登录成功public static boolean login(String username,String password) {Connection conn = null;Statement s = null;ResultSet rs = null;try {// 1加载驱动Class.forName("com.mysql.jdbc.Driver");// 2获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/java2403?useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimeZone=UTC","root", "123456");// 3获得执行语句对象s = conn.createStatement( );String sql = "select * from tb_user where username = '"+username+"' and password = '"+password+"'";System.out.println("拼接后的sql: " + sql );// 4执行sqlrs = s.executeQuery(sql);if (rs.next()) {return true;}} catch (Exception e) {e.printStackTrace( );} finally {// 5关流try {rs.close();s.close( );conn.close( );} catch (SQLException e) {e.printStackTrace( );}}return false;}
}