import java.sql.*;
import java.util.*;

public class Hello {
    public static void main(String[] args) throws Exception {
        Connection conn = null;
        Statement stmt = null;
        PreparedStatement ps = null;
        ResultSet rset = null;
        ResultSetMetaData md = null;
        Class.forName("org.postgresql.Driver");
        conn = DriverManager.getConnection("jdbc:postgresql://localhost/pg_demo");
//        conn.setAutoCommit(false);
//        stmt = conn.createStatement();
//        stmt.setFetchSize(1);  // <----- Turn on stream ResultSet
//        rset = stmt.executeQuery("SELECT * from users;");
        rset = conn.getMetaData().getColumns(null, "public", "users", null);
        md = rset.getMetaData();

        // Close the connection
        conn.close();

        // Let's say I don't know what's in the database but I want to retrieve its content
        // Here there is no exception
        ArrayList<ArrayList<Object>> results = new ArrayList<>();
        while(rset.next()) {
            ArrayList<Object> row = new ArrayList<>();
            for (int i = 1; i <= md.getColumnCount(); i++){
                row.add(rset.getObject(i));
            }
            results.add(row);
        }

//        // Close the connection
//        conn.close();

        System.out.println(String.format("-> Result Size: %s", results.size()));
        // for Comdb2 -> Result Size: 0
        // for Postgres -> Result Size: 10

        // Print the results correctly for postgres but don't display anything for comdb2 (nothing in the list)
        for (int rowIndex = 0; rowIndex < results.size(); rowIndex++){
            ArrayList<Object> row = results.get(rowIndex);
            for (int columnIndex = 0; columnIndex < row.size(); columnIndex++){
                Object value = row.get(columnIndex);
                if (value != null)
                    System.out.println(String.format("(Row %s, Column %s): %s", rowIndex, columnIndex, row.get(columnIndex).toString()));
                else
                    System.out.println(String.format("(Row %s, Column %s): null", rowIndex, columnIndex));
            }
        }
    }
}