Randomly generate an eight-digit discount code and save it to the MySQL database

import java.util.Random;
/**
*Function: Randomly generate discount codes*@author iamwiam
*
*/
public class ActivatedCode {
 public int ACTIVATEDCODENUM = 200; //Number of coupon codes generated Random random = new Random();
 String candicatedCode = "abcedefghijklmnopqrstuvwxyz"; //The discount code contains lowercase letters candicatedCode+=candicatedCode.toUpperCase(); //The discount code contains uppercase letters candicatedCode+="1234567890"; //The discount code contains Arabic numerals for(int i=0; i< ACTIVATEDCODENUM; i++){
  String res = "";
  for(int j=0;j<8;j++){
   res+=candicatedCode.charAt(random.nextInt(candicatedCode.lenght()));
  }
  System.out.println(res); //Randomly generate 200 8-digit discount codes}
}

private static void insertToMySql(String res){ 
int n = 0; 
try{ 
Class.forName("com.mysql.jdbc.Driver"); 
Connection connection = DriverMannager.getConnection("jdbc:mysql://127.0.0.1/tb_act_code","zy","IamWiam"); 
String sql = "insert into checkNum(value) values(?)"; 
PreparedStatement ps = connection.prepareStatement(sql); 
ps.setObject(1,res); //The order of placeholders starts from 1, the first parameter is the position of the placeholder, and the second parameter is the value of the placeholder n = ps.executeUpdate(); 
}catch(ClassNotFoundException e){ 
e.printStackTrace(); 
}catch(SQLException e){ 
e.printStackTrace(); 
} 
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Random;
/**
 * Function: Randomly generate discount codes * @author iamwiam
 *
 */
public class ActivatedCode {
 public static void main(String[] args) {
  final int ACTIVATEDCODENUM = 200;
  Random random = new Random();
  String candicatedCode = "abcdefghijklmnopqrstuvwxyz";
  candicatedCode+=candicatedCode.toUpperCase();
  candicatedCode+="1234567890";
  for(int i=0;i<ACTIVATEDCODENUM;i++){
   String res = "";
   for(int j=0;j<8;j++){
    res+=candicatedCode.charAt(random.nextInt(candicatedCode.length()));
   }
// String pwd = Activatedcode.getMD5(Activatedcode.getMD5(res));
   insertToMysql(res);
  }
 }
 private static void insertToMysql(String res) {
  int n=0;
  try {
   Class.forName("com.mysql.jdbc.Driver");
   Connection connection = DriverManager.getConnection(
     "jdbc:mysql://127.0.0.1/new2017", "zy", "IamWiam");
   String sql = "insert into checkNum(value) values(?)";
   PreparedStatement ps = connection.prepareStatement(sql);
   ps.setObject(1, res);
   n = ps.executeUpdate();
  } catch (ClassNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
 }
}