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