public class User {

  private String name;
  private String loginname;
  private String loginpsw;
  public String getName() {
   return name;
  }
  public void setName(String name) {
   this.name = name;
  }
  public String getLoginname() {
   return loginname;
  }
  public void setLoginname(String loginname) {
   this.loginname = loginname;
  }
  public String getLoginpsw() {
   return loginpsw;
  }
  public void setLoginpsw(String loginpsw) {
   this.loginpsw = loginpsw;
  }
}
//用于注册和登陆的小小代码块
package 登陆判断;

import java.util.Scanner;

public class In {

  public static User getUser(){
   User u = new User();
   Scanner sc = new Scanner(System.in);
   System.out.println("请输入登陆名");
   u.setLoginname(sc.nextLine());
   System.out.println("请输入密码");
   u.setLoginpsw(sc.nextLine());
   return  u;
  }
  public static User registerUser(){
   User u = new User();
   Scanner sc = new Scanner(System.in);
   System.out.println("请注册用户名名");
   u.setName(sc.nextLine());
   System.out.println("请注册登陆名");
   u.setLoginname(sc.nextLine());
   System.out.println("请注册密码");
   u.setLoginpsw(sc.nextLine());
   return  u;
  }
}

//登陆时的检查，判断登陆名和密码是否正确，正确则返回 用户名
package 登陆判断;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class Check {

  public static void checkUser(User u)
  {
   try {
    Class.forName("oracle.jdbc.driver.OracleDriver");
   } catch (ClassNotFoundException e) {
    e.printStackTrace();
   }
   String url = "jdbc:oracle:thin:@localhost:1521:orcl";
   String user = "scott";
   String password = "tiger";
   Connection conn = null;
   ResultSet rs = null;
   PreparedStatement pst = null;

   String sql = "Select name from USERINFO where loginname = ? and loginpsw = ? ";
   try {
    conn = DriverManager.getConnection(url, user, password);
    pst = conn.prepareStatement(sql);
    pst.setString(1, u.getLoginname());
    pst.setString(2,u.getLoginpsw());
    rs = pst.executeQuery();
    while(rs.next()){
     u.setName(rs.getString(1));
    }    
   } catch (SQLException e) {
    e.printStackTrace();
   }finally{
    try {
     rs.close();
     pst.close();
     conn.close();
    } catch (SQLException e) {
     e.printStackTrace();
    }
   }
   if(u.getName() == null || u.getName().isEmpty()){
    System.out.println("登陆失败");
   }else{
    System.out.println("欢迎"+u.getName()+"登陆");
   }

  }
}

//注册界面，要判断 登陆名是否有重复，有重复则注册失败。有点小疑问，已用注释标出来
package 登陆判断;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class Register {

  public static void registUser(User u){

   try {
    Class.forName("oracle.jdbc.driver.OracleDriver");
   } catch (ClassNotFoundException e) {
    e.printStackTrace();
   }
   String url = "jdbc:oracle:thin:@localhost:1521:orcl";
   String user = "scott";
   String password = "tiger";
   Connection conn = null;
   String sql = "Insert Into USERINFO values(?,?,?)";
   PreparedStatement pst = null;

   //判断登陆名是否已经存在
   Statement s = null;
   ResultSet rs = null;
   String sql_ck = "Select LOGINNAME FROM USERINFO";
   try {
    conn = DriverManager.getConnection(url, user, password);
    pst = conn.prepareStatement(sql);
    pst.setString(1, u.getName());
    pst.setString(2, u.getLoginname());
    pst.setString(3, u.getLoginpsw());
    //判断登陆名是否已经存在
    s = conn.createStatement();
    rs = s.executeQuery(sql_ck);
    while(rs.next()){//为什么用 rs.getString(2)会提示 无效的索引呢
     if( rs.getString("LOGINNAME").equals(u.getLoginname()) ){
      System.out.println("登陆名已经存在，注册失败");
      break;
     }else{
      pst.executeUpdate();
      System.out.println("注册成功");
      break;
     }
    } 
   } catch (SQLException e) {
    e.printStackTrace();
   }finally{
    try {
     rs.close();
     pst.close();
     s.close();
     conn.close();
    } catch (SQLException e) {
     e.printStackTrace();
    }
   }

   
  }
}
//main界面//
//数据库中表的结构式这样
//name(用户名，用于显示),
//loginname(登录名,即登陆时输入的ID)
//loginpsw(登陆时输入的密码)
package 登陆判断;

import java.util.Scanner;

public class Test {

 public static void main(String[] args) {

  int chos = 0;
  Scanner sc = new Scanner(System.in);
  System.out.println("tt登陆请按1tt注册请按2");
  chos = sc.nextInt();
  switch(chos){
  case 1: Check.checkUser(In.getUser());break;
  case 2: Register.registUser(In.registerUser());break;
  default: System.out.println("请输入正确的选择");break;
  }
 }

}