java+mysql的简单登录验证及一些小功能

package shujukv.nn;
/*
 * java简单数据库验证登录及小功能
 */
import java.sql.Statement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Scanner;
public class Test1 {
  static Connection con;
  static Scanner p1=new Scanner(System.in);
  static String url="jdbc:mysql://localhost:3306/userdemo2";        //相当于路径
  static String username="root";                      //登录名 
  static String password="1998";
  static PreparedStatement p;
  static ResultSet res;
  static String sql;
  static Scanner n=new Scanner(System.in);
  static int i=0;
  public  static Connection getConnection() {
    try {
      Class.forName("com.mysql.jdbc.Driver");
      System.out.println("数据库正在连接");
    }catch(Exception e) {
      e.printStackTrace();
    }
    try {
//      for(int i=0;i<6;i++)
//      {
//        Thread.sleep(600);
//        System.out.print("#  ");
//      }
      System.out.println();
      con=DriverManager.getConnection(url, username, password);
      System.out.println("数据库连接成功");
    } catch (Exception e) {
      e.printStackTrace();
    }
    return con;
  }
  //main函数
  public static void main(String[] args) throws Exception {
    getConnection();
    int m=0;
    while(m!=5) {
      System.out.println("欢迎使用T.T租机！");
      System.out.println("1.注册账户");
      System.out.println("2.登录系统");
      System.out.println("3.管理员登录");
      System.out.println("4.找回密码");
      System.out.println("5.退出");
      System.out.println("请输入数字选择功能");
      m=n.nextInt();
      switch(m) {
      case 1:zhuce();break;
      case 2:denglu();break;
      case 3:guanliyuan();break;
      case 4:mhchaxun();break;
      case 5:break;
    }
  }
  }
  //登录
public static void denglu() throws SQLException {
    System.out.println("请输入你的账号:");
    String a=n.next();
    System.out.println("请输入你的密码:");
    String b=n.next();
       sql = "select username,password from user where username=? and password=?";      //预处理
       p=con.prepareStatement(sql);       //标记
       p.setString(1, a);
       p.setString(2, b);
       res=p.executeQuery();
    if(res.next()) {
      System.out.println("登陆成功");
    }
    else {
      i++;
      if(i==3) {
        Break(i);
      }
      System.out.println("登录失败,请重新登录！");
      denglu();
      }
    } 
public static  void guanliyuan() throws SQLException {
  System.out.println("请输入你的admin账号:");
  String a=n.next();
  System.out.println("请输入你的admin密码:");
  String b=n.next();
       sql = "select username,password from useradmin where username=? and password=?";     //预处理
       p=con.prepareStatement(sql);       //标记
       p.setString(1, a);
       p.setString(2, b);
       res=p.executeQuery();
    if(res.next()) {
      System.out.println("登陆成功");
    }
    else {
      i++;
      if(i==3) {
        Break(i);
      }
      System.out.println("登录失败,请重新登录！");
      denglu();
      }
    } 
  //注册
  public static void zhuce()throws SQLException, InterruptedException {
    System.out.println("请输入你的新账号：");
    String a=n.next();
    sql="select username from user where username=?";   //预处理验证
    p=con.prepareStatement(sql);
    p=con.prepareStatement(sql);
    p.setString(1, a);
    res=p.executeQuery();
  if(res.next()) {
    System.out.println("此账号已注册,请重新输入");
    zhuce();
  }
  else {
    int k=0;
    while(k==0){
    System.out.println("请输入你的登录密码");
    String b=n.next();
    System.out.println("请再次输入你的确认密码");
    String b22=n.next();
    if(b.equals(b22)) {
      //判断两次输入的密码是否相同
      System.out.println("请输入你找回密码的问题:");
      String b3=n.next();
      System.out.println("请输入问题的答案:");
      String b33=n.next();
      String sql2="insert into user(username,password,userwt,userda) values(?,?,?,?)";
      java.sql.PreparedStatement res3=con.prepareStatement(sql2);
      res3.setString(1, a);
      res3.setString(2, b);
      res3.setString(3, b3);
      res3.setString(4, b33);
      res3.execute();
      System.out.println("注册成功!");
      k=1;
      System.out.println("你的账号为:"+a);
      System.out.println("你的密码为:"+b);
    }
    else {
      System.out.println("两次输入的密码不一致，请重新输入");
    }
    }
  }
}
  //找密码
  //预设问题提示回答验证
  //根据账号 模糊查询
  public static void mhchaxun() throws Exception {
    System.out.println("请输入你的账号:");
    String k=p1.next();
  sql="select * from user where username=?";
  p=con.prepareStatement(sql);
  p.setString(1, k);
  res=p.executeQuery();
  if(res.next()) {
    System.out.println(res.getString(4));
    Thread.sleep(500);
    System.out.println("请输入你的问题答案");
    chazhao(k);
  }
  else {
    mhchaxun();
  }
  }
  //根据问题查找
  public static void chazhao(String kk) throws Exception  {
    String k=p1.next();
  p=con.prepareStatement("select * from user where userda=? and username=?");
  p.setString(1, k);
  p.setString(2, kk);
  res=p.executeQuery();
  if(res.next()) {
    System.out.println("核对正确，请输入新密码:");
    String k1=n.next();
    xgpassword(k1,kk);
  }else {
      ++i;
      if(i==3) {
        Break(i);
      }
      System.out.println("答案错误！,请重新输入");
      chazhao(kk);
    }
  }
    //强行退出提醒
  public static void Break(int a) {
      System.out.println("你已错误3次，已强行退出");
      System.exit(0);
    }
  //修改密码
  public static void xgpassword(String k1,String K2) throws Exception {
    sql="update user set password=? where username=?";
    p=con.prepareStatement(sql);
    p.setString(1, k1);
    p.setString(2, K2);
    p.executeUpdate();
    System.out.println("修改成功，即将返回登录界面————");
    Thread.sleep(1000);
  }
}