public ArrayList querryCategory() {
		String sql = "select * from bookcategory";
		DBManager dbm = null;
		Connection conn= null;
		Statement stmt = null;
		ResultSet rs = null;
		ArrayList categoryList = null;
		try {
			dbm = new DBManager();
			conn = dbm.getConnection();
			stmt = conn.createStatement();
			categoryList = new ArrayList();
			rs = stmt.executeQuery(sql);
			
			while(rs.next()) {
				BookCategory bc =new BookCategory();
				bc.setId(rs.getInt(1));
				bc.setName(rs.getString(2));
				categoryList.add(bc);
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			dbm.closeAll(rs,stmt,conn);
			return categoryList;
		}
	}