import java.util.Random;
import java.util.UUID;

public class Dept {

	/**
	 * 生成随机字符串 uuid
	 */
	public static String getUUID() {
		return UUID.randomUUID().toString();
	}

	/**
	 * 生成随机字符串 uuid 将"-"替换为""
	 */
	public static String getUUNUM() {
		return UUID.randomUUID().toString().replace("-", "");
	}

	/**
	 * 生成指定位数的随机数
	 * @param n 生成的随机数的位数
	 */
	public static String getRandom(int n) {
		Random r = new Random();
		Long b = Math.abs(r.nextLong());
		return b.toString().substring(0, n);
	}

	public static void main(String[] args) {
		System.out.println(getUUNUM());
		System.out.println(getUUID());
		System.out.println(getRandom(6));
	}

}

//length用户要求产生字符串的长度
 public static String getRandomString(int length){
   String str="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
   Random random=new Random();
   StringBuffer sb=new StringBuffer();
   for(int i=0;i<length;i++){
    int number=random.nextInt(62);
    sb.append(str.charAt(number));
   }
   return sb.toString();
 }

//可以指定字符串的某个位置是什么范围的值
 public static String getRandomString2(int length){
  Random random=new Random();
  StringBuffer sb=new StringBuffer();
  for(int i=0;i<length;i++){
    int number=random.nextInt(3);
    long result=0;
    switch(number){
     case 0:
       result=Math.round(Math.random()*25+65);
       sb.append(String.valueOf((char)result));
       break;
     case 1:
       result=Math.round(Math.random()*25+97);
       sb.append(String.valueOf((char)result));
       break;
     case 2:   
       sb.append(String.valueOf(new Random().nextInt(10)));
       break;
    }


   }
   return sb.toString();
 }

String filename=RandomStringUtils.randomAlphanumeric(10);