private String combind(Collection<?> c, String conStr){
		StringBuilder sb = new StringBuilder();
		if(c== null || c.isEmpty()){
			return null;
		}
		Iterator<?> iter = c.iterator();
		while(iter.hasNext()){
			sb.append(iter.next());
			if(iter.hasNext()){
				sb.append(conStr);
			}
		}
		return sb.toString();
	}