public static void authorsImport() throws ClassNotFoundException, SQLException {
        Class.forName("org.postgresql.Driver");
        c = DriverManager.getConnection("jdbc:postgresql://localhost:5432/postgres", "postgres", "qqkfq0513");
        stmt = c.createStatement();
        sql = "select * from authors";
        ResultSet rs = stmt.executeQuery(sql);
        while (rs.next()) {
            int cluster = rs.getInt("cluster");
            int pid = rs.getInt("pid");
            if (authorCluster.containsKey(pid)) {
                HashSet<Integer> tempSet = authorCluster.get(pid);
                tempSet.add(cluster);
                authorCluster.put(pid, tempSet);
            } else {
                HashSet<Integer> tempSet = new HashSet<>();
                tempSet.add(cluster);
                authorCluster.put(pid, tempSet);
            }
        }
        for (int pub : authorCluster.keySet()) {
            HashSet<Integer> temp = authorCluster.get(pub);
            if (realCluster.containsKey(temp)) {
                HashSet<Integer> temp2 = realCluster.get(temp);
                temp2.add(pub);
                realCluster.put(temp, temp2);
            } else {
                HashSet<Integer> temp2 = new HashSet<>();
                temp2.add(pub);
                realCluster.put(temp, temp2);
            }
        }

    }