CharacterUtils.java

package util;

import java.util.Random;

public class CharacterUtils {  
      
    public static String getRandomString(int length){  
        String str="abcdefABCDEF0123456789";  
        Random random = new Random();  
        StringBuffer sb = new StringBuffer();  
          
        for(int i = 0 ; i < length; ++i){  
            int number = random.nextInt(22);//[0,62)  
              
            sb.append(str.charAt(number));  
        }  
        return sb.toString();  
    }

  
    public static void main(String[] args){  
    	System.out.println(getRandomString(4));
    }  
}