Java程序登录-2011年09月14日

     登录

1.       获取用户输入的用户名, 根据用户名查找数据库中是否存在该记录.

2.       如果没有找到, 提示用户名不存在重新输入.

3.       如果存在, 将数据库中数据封装成User对象返回.

4.       获取用户输入的密码, 和User对象密码进行比较, 如果不同则提示重新输入.

5.       密码正确提示登录成功, 将User中name, email, birthday显示.

import java.sql.*; import java.util.Scanner;   public class Login {     String userName = "";     String password = "";       public Login() {        getInfo();        Connection con = null;        Statement stmt = null;        ResultSet rs = null;          try {            con = DriverManager.getConnection("jdbc:mysql://localhost/loginDb",                   "root", "admin");            stmt = con.createStatement();            String sql = "select username,password from user";            rs = stmt.executeQuery(sql);              while (rs.next()) {               if (rs.getString(1).equals(userName)                      && rs.getString(2).equals(password)) {                   System.out.println("验证无误，可以登录！！！");                   return;               }            }              System.out.println("用户名不存在或密码错误....");            // 考虑如修改代码使能够判断用户名不存在还是密码输入错误        } catch (SQLException e) {            e.printStackTrace();        } finally {            try {               rs.close();               stmt.close();               con.close();            } catch (SQLException e) {               // TODO Auto-generated catch block               e.printStackTrace();            }        }     }       public Login(boolean userPreparedStatement) {        // getInfo();        userName = "root";        password = "123";          Connection con = null;        PreparedStatement pstmt = null;        ResultSet rs = null;          try {            con = DriverManager.getConnection("jdbc:mysql://localhost/loginDb",                   "root", "admin");            pstmt = con                   .prepareStatement("select * from user where username = ? and password = ?");              pstmt.setString(1, userName);            pstmt.setString(2, password);              rs = pstmt.executeQuery();              ResultSetMetaData rsmd = rs.getMetaData();              while (rs.next()) { // 调试代码               if (rsmd != null) {                   for (int i = 1; i <= rsmd.getColumnCount(); i++) {                      System.out.print(rsmd.getColumnName(i) + "\t"                             + rs.getString(i) + "\t");                   }                   System.out.println("");               }            }            // 验证用户名密码            rs.beforeFirst();            while (rs.next()) {               System.out.println("验证无误，可以登录！！！");               return;            }              System.out.println("用户名不存在或密码错误....");            // 考虑如修改代码使能够判断用户名不存在还是密码输入错误        } catch (SQLException e) {            e.printStackTrace();        } finally {            try {               rs.close();               pstmt.close();               con.close();            } catch (SQLException e) {               // TODO Auto-generated catch block               e.printStackTrace();            }        }     }       public void getInfo() {        Scanner s = new Scanner(System.in);        System.out.println("请输入用户名：");        userName = s.nextLine().trim();        System.out.println("请输入密码：");        password = s.nextLine().trim();     }       public static void main(String[] args) {        // new Login();        new Login(true);     } }