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;
  }
}
//用于注冊和登陸的小小代碼塊
package 登陸判斷;

import java.util.Scanner;

public class In {

  public static User getUser(){
   User u = new User();
   Scanner sc = new Scanner(System.in);
   System.out.println("請輸入登陸名");
   u.setLoginname(sc.nextLine());
   System.out.println("請輸入密碼");
   u.setLoginpsw(sc.nextLine());
   return  u;
  }
  public static User registerUser(){
   User u = new User();
   Scanner sc = new Scanner(System.in);
   System.out.println("請注冊用戶名名");
   u.setName(sc.nextLine());
   System.out.println("請注冊登陸名");
   u.setLoginname(sc.nextLine());
   System.out.println("請注冊密碼");
   u.setLoginpsw(sc.nextLine());
   return  u;
  }
}

//登陸時的檢查，判斷登陸名和密碼是否正確，正確則返回 用戶名
package 登陸判斷;

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("登陸失敗");
   }else{
    System.out.println("歡迎"+u.getName()+"登陸");
   }

  }
}

//注冊界面，要判斷 登陸名是否有重復，有重復則注冊失敗。有點小疑問，已用注釋標出來
package 登陸判斷;

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;

   //判斷登陸名是否已經存在
   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());
    //判斷登陸名是否已經存在
    s = conn.createStatement();
    rs = s.executeQuery(sql_ck);
    while(rs.next()){//為什么用 rs.getString(2)會提示 無效的索引呢
     if( rs.getString("LOGINNAME").equals(u.getLoginname()) ){
      System.out.println("登陸名已經存在，注冊失敗");
      break;
     }else{
      pst.executeUpdate();
      System.out.println("注冊成功");
      break;
     }
    } 
   } catch (SQLException e) {
    e.printStackTrace();
   }finally{
    try {
     rs.close();
     pst.close();
     s.close();
     conn.close();
    } catch (SQLException e) {
     e.printStackTrace();
    }
   }

   
  }
}
//main界面//
//數據庫中表的結構式這樣
//name(用戶名，用于顯示),
//loginname(登錄名,即登陸時輸入的ID)
//loginpsw(登陸時輸入的密碼)
package 登陸判斷;

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("/t/t登陸請按1/t/t注冊請按2");
  chos = sc.nextInt();
  switch(chos){
  case 1: Check.checkUser(In.getUser());break;
  case 2: Register.registUser(In.registerUser());break;
  default: System.out.println("請輸入正確的選擇");break;
  }
 }

}