如何使用jdbc将数据从postgresql导出到.csv文件？

Question

我想按日期在表中导出数据,所以我用jdbc编写了一个java程序.

  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;
        }
    }

这个编程在服务器上运行,而数据库是另一个服务器,我在这个程序中连接到数据库.但是当我在服务器上运行程序时,我收到一个错误,只有超级用户可以复制到文件或从文件复制:

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)

我在线搜索解决方案,并试图使用psql'\ copy'命令,但在编译时,另一个错误说'\'是java中的无效转义字符所以我写了"双斜线COPY",这在运行程序时出现语法错误.

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

任何人都知道如何让程序执行或解决"\ copy"中无效转义字符的问题？

Answer 1

我建议使用CopyManager.

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)", fileOutputStream);

此方法不要求您成为超级用户,并将输出文本正确格式化为CSV