JAvaランダムにカスタム範囲を生成する時間

package com.wyx.hibernate;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Random;

import org.hibernate.Session;

import com.wyx.hibernate.utils.HibernateUtils;

public class InitData {
	public static void main(String[] args) {
		addStudent();
		addwuye();
	}
	
	public static void addStudent(){
		for(int i = 1; i <= 10; i++){
			Group group = new Group();
			group.setName("  "+i);
			for(int j = 1; j<= 10; j++){
				
				User user = new User();
				
				//           
				user.setCreateTime(randomDate("2008-8-8","2011-3-28"));
				user.setName("  "+i+"   " + j );
				user.setGroup(group);
				Session session = HibernateUtils.getSession();
				session.beginTransaction();
				try {
					session.save(user);
					session.getTransaction().commit();
				} catch (Exception e) {
					e.printStackTrace();
					session.getTransaction().rollback();
				}finally{
					HibernateUtils.closeSession(session);
				}	
			}
			
		}
		
	}
	
	public static void addwuye(){
		for(int i = 1; i <= 10; i++){
				User user = new User();
				user.setCreateTime(new Date());
				user.setName("    "+i);
				Session session = HibernateUtils.getSession();
				session.beginTransaction();
				try {
					session.save(user);
					session.getTransaction().commit();
				} catch (Exception e) {
					e.printStackTrace();
					session.getTransaction().rollback();
				}finally{
					HibernateUtils.closeSession(session);
				}	
		}
			
	}
	 //         
	  private static Date randomDate(String beginDate, String endDate) {   
	         try {   
	             SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");   
	             Date start = format.parse(beginDate);//          
	             Date end = format.parse(endDate);//          
	             // getTime()      1970   1   1   00:00:00 GMT     Date         。   
	             if (start.getTime() >= end.getTime()) {   
	                 return null;   
	             }   
	             long date = random(start.getTime(), end.getTime());   
	   
	             return new Date(date);   
	         } catch (Exception e) {   
	             e.printStackTrace();   
	         }   
	         return null;   
	     }   
	   
	     private static long random(long begin, long end) {   
	         long rtn = begin + (long) (Math.random() * (end - begin));   
	         //                ，                
	         if (rtn == begin || rtn == end) {   
	             return random(begin, end);   
	         }   
	         return rtn;   
	     } 
		

}