按字节截取字符串、随即生成汉字

/**
	 * 按字节截取字符串，不取不完整的字符（从一开始 ）
	 * @param str 被截取的数
	 * @param start 开始字节数
	 * @param limit 截取的字节数量
	 * @return
	 */
	public static String subStringByType(String str, int start, int limit){
		start = --start;	// 从一开始 
		
		byte[] ss = str.getBytes();
		
		int x = 0;
		while(ss[start-x] < 0){
			if(start-x == 0){
				x++;
				break;
			}
			x++;
		}
		if(x%2 == 0 && x != 0){
			start = --start;
			x = ++x;	// start 左移，那 x 循环次数也得增加
		}

		int y = 0;
		while(ss[start+limit-1-y] < 0){
			if(limit-1-y == 0){
				y = y+x;
				break;
			}
			y++;
		}
		
		if(y%2 != 0)
			limit = ++limit;
		
		return new String(ss, start, limit);
	}
	
	/**
	 * 随即生成汉字
	 * @return
	 */
	public static String getChinese(){  
        Random random=new Random();  
        String ctmp="";  
        String[] rBase={"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"};  
        //生成第一位区码  
        int r1=random.nextInt(3)+11;  
        String str_r1=rBase[r1];  
          
        //生成第二位区码  
        int r2;  
        if(r1==13){  
            r2=random.nextInt(7);  
        }else{  
            r2=random.nextInt(16);  
        }  
        String str_r2=rBase[r2];  
        //第三位的位码  
        int r3=random.nextInt(6)+10;  
        String str_r3=rBase[r3];  
        //第四位的位码  
        int r4;  
        if(r3==10){  
            r4=random.nextInt(15)+1;  
        }else if(r3==15){  
            r4=random.nextInt(15);  
        }else{  
            r4=random.nextInt(16);  
        }  
        String str_r4=rBase[r4];  
          
        byte[] bytes=new byte[2];  //定义二维数组，用以保存汉字  
        String str_r12=str_r1+str_r2;  
        int tempLow=Integer.parseInt(str_r12,16);   
        bytes[0]=(byte)tempLow;  
          
        String str_r34=str_r3+str_r4;  
        int tempHigh=Integer.parseInt(str_r34,16);  
        bytes[1]=(byte)tempHigh;  
          
        ctmp=new String(bytes);  
        
        return ctmp;  
    }