how to export data from postgresql to .csv file using jdbc?

Question

I want to export data in a table by date, so I write a java program using jdbc.

  public void exportData(Connection conn,String filename) {

        Statement stmt;
        String query;
        try {
            stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
                    ResultSet.CONCUR_UPDATABLE); 

            SimpleDateFormat dateFormat = new SimpleDateFormat ("yyyy-MM-dd hh:mm:ss");
            Date startDate = dateFormat.parse("2014-08-21 00:00:00");
            Date endDate = dateFormat.parse("2014-08-22 00:00:00");

            Calendar startCalendar = Calendar.getInstance();
            startCalendar.setTime(startDate);

            Calendar endCalendar = Calendar.getInstance();
            endCalendar.setTime(endDate);

            Calendar thisDayCalendar = startCalendar;

            while(!thisDayCalendar.after(endCalendar)){
                Date thisDayDate = thisDayCalendar.getTime();
                thisDayCalendar.add(Calendar.DATE, 1);
                Date nextDayDate = thisDayCalendar.getTime();

                String thisDayString = dateFormat.format(thisDayDate);
                String nextDayString = dateFormat.format(nextDayDate);

                SimpleDateFormat dateFormat1 = new SimpleDateFormat ("yyyy-MM-dd");
                String fileDateString = dateFormat1.format(thisDayDate);

                //For comma separated file
                query ="COPY (SELECT * FROM signals WHERE date_time >= '" + thisDayString + 
                        "' AND date_time < '" +nextDayString + "' ) TO " +filename + fileDateString + ".csv  delimiter ','";

                stmt.executeQuery(query);  
            //System.out.println(query);

            }

        } catch(Exception e) {
            e.printStackTrace();
            stmt = null;
        }
    }

This programming is running on a server while the database is another sever, I connect to the database in this program.But when I run the program on server, I got an error that only superuser can COPY to or from a file:

org.postgresql.util.PSQLException: ERROR: must be superuser to COPY to or from a file
  Hint: Anyone can COPY to stdout or from stdin. psql's \copy command also works for anyone.
        at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2161)
        at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1890)
        at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:560)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:283)
        at DBase.exportData(ExportSignal.java:85)
        at ExportSignal.main(ExportSignal.java:23)

I searched solutions online and tried to use psql '\\copy' command but when compiling,another error said '\\' is invalid escape character in java so I wrote "double slashes COPY" which made syntax error when running the program.

query ="\COPY (SELECT * FROM signals WHERE date_time >= '" + thisDayString + 
                            "' AND date_time < '" +nextDayString + "' ) TO " +filename + fileDateString + ".csv  delimiter ','";

Dose anyone know how to make the program execute or solve the problem about invalid escape character in "\\copy"?

Answer 1

I would recommend using CopyManager for this.

Connection connection = DriverManager.getConnection(url);
CopyManager copyManager = new CopyManager((BaseConnection) connection);
File file = new File("/tmp/output.csv");
FileOutputStream fileOutputStream = new FileOutputStream(file);

//and finally execute the COPY command to the file with this method:
copyManager.copyOut("COPY (" + query + ") TO STDOUT WITH (FORMAT CSV, HEADER)", fileOutputStream);

This method does not require you to be superuser and will correctly format the output text as CSV

Answer 2

The error shows ERROR: must be superuser to COPY to or from a file

It seems that the current user is not having enough permissions to write the file. Provide permissions to the write location for the user or execute the program from a user account which has sufficient privileges to write to the file.