private void readFromDb() {
		BasicDBObject doc = new BasicDBObject();
		DBCursor cursor = this.cate.find(doc);
		try {
			while (cursor.hasNext()) {
				DBObject obj = cursor.next();
				for (String key : obj.keySet()) {
					if (key.equals("_id")) {
						continue;
					}
					BasicDBList category = (BasicDBList) obj.get(key);
					List<String> list = new ArrayList<String>();
					for (Object s : category) {
						list.add((String) s);
					}
					categories.put(key, list);
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}