隨機長度字符串

public static String getStrNumRandom(Integer length) {  
	        StringBuilder str = new StringBuilder();
	        Random random = new Random();  
	        for (int i = 0; i < length; i++) {  
	            boolean b = random.nextBoolean();  
	            if (b) { // 字符串  
	                int choice = random.nextBoolean() ? 65 : 97; //取得65大寫字母還是97小寫字母  
	                str.append((char) (choice + random.nextInt(26)));// 取得大寫字母  
	            } else { // 數字  
	                str.append(random.nextInt(10));  
	            }  
	        }  
	        return str.toString();  
	    }