How do I write a multi line file with Writer?

I had success looping through my 5 database rows and writing a CSV file, except the code that I used rewrote the file every line. I will use the CSVParser to read the file to import an activity from another computer. The examples I found online for append are few.

Can I start the Writer with append as true, or is there a better way to write the file. I used the following to write the CSV line from the String d built from the row of the database:

                try (Writer w = new OutputStreamWriter(fs.openOutputStream(String.valueOf(sendFile)))) {
                    w.write(d);
                } catch (Exception e) {
                    Log.p("Error " + e);
                }

Thanks.

Edit 1: This is the method I use to read the database into strings. Both Writer, as Shai showed me before (shown above), and writeToSting illustrated below (with \n added to the string) overwrite row 1 with row 2, etc. and at conclusion give a csv file with only row 5.

    public void toSVC(addActivity c) throws IOException, InstantiationException {
        namet = c.name.toString();
        dbsa = Display.getInstance().openOrCreate("pandr.db");
        String rd = "SELECT * FROM pandr WHERE name ='" + namet + "'";
        cursa = dbsa.executeQuery(rd);
        Row currentRow = cursa.getRow();
        cc = currentRow.getInteger(3);
        x = cc + 1;
        rn = 1;
        for (r = 1; r < x; r++) {
            trecno = rn.toString();
            tname = currentRow.getString(1);
            tpos = currentRow.getInteger(2);
            posv = tpos.toString();
            ttr = currentRow.getInteger(3);
            trv = ttr.toString();
            tbloc = currentRow.getString(4);
            tlwloc = currentRow.getString(5);
            tcfloc = currentRow.getString(6);
            trwloc = currentRow.getString(7);
            tamloc = currentRow.getString(8);
            tcmloc = currentRow.getString(9);
            tdmloc = currentRow.getString(10);
            tlcbloc = currentRow.getString(11);
            trcbloc = currentRow.getString(12);
            tlfbloc = currentRow.getString(13);
            trfbloc = currentRow.getString(14);
            tgloc = currentRow.getString(15);
            String d = trecno + "," + tname + "," + posv + "," + trv + "," + tbloc + "," + tlwloc + "," + tcfloc + "," + trwloc + "," + tamloc + "," + tcmloc + "," + tdmloc + "," + tlcbloc + "," + trcbloc + "," + tlfbloc + "," + trfbloc + "," + tgloc+"\n";
            String flname = new String("/" + namet + ".csv");
            FileSystemStorage fs = FileSystemStorage.getInstance();
            File sendFile = new File(fs.getAppHomePath() + flname);
            Util.writeStringToFile(sendFile, d);
            rn++;
        }
        dbsa.close();
        cursa.close();
        Util.cleanup(os);
        new FinishBanner();
    }
}

I first moved the Writer builder outside the loop, and tried w.write(d) for each row, but that gave me a java.lang.NullPointerException on row 2.

I also tried to use StringBuilder and sb.append(d) (with \n included at the end of the string) to the StringBuilder for the 5 rows, but sb.append(d) also gave me a java.lang.NullPointerException when trying to write the first line to the StringBuilder.

I thought the easiest way to accomplish this was create the file and append each row to the file, which is why I thought StringBuilder.append() would work. I am finding there aren't any website documents showing a way to accomplish this.

My goal is still to write a file that I can email and parse, and write into the activity database on a different device.

Edit 2 In my work to get the data order correct, I left off cursa.next(), which was why I got line 1 repeated. If I went back to my original code, Writer would work.

A new problem has manifest with this method. The StringBuilder sb has the first line twice. I increased x to 7, and the StringBuilder showed line 5 from the database as line 6 in sb.

Here is the current loop with the same head as above:

        for (r = 1; r < x; r++) {
            trecno = rn.toString();
            tname = currentRow.getString(1);
            tpos = currentRow.getInteger(2);
            posv = tpos.toString();
            ttr = currentRow.getInteger(3);
            trv = ttr.toString();
            tbloc = currentRow.getString(4);
            tlwloc = currentRow.getString(5);
            tcfloc = currentRow.getString(6);
            trwloc = currentRow.getString(7);
            tamloc = currentRow.getString(8);
            tcmloc = currentRow.getString(9);
            tdmloc = currentRow.getString(10);
            tlcbloc = currentRow.getString(11);
            trcbloc = currentRow.getString(12);
            tlfbloc = currentRow.getString(13);
            trfbloc = currentRow.getString(14);
            tgloc = currentRow.getString(15);
            sb.append(trecno).append(",")
                        .append(tname).append(",")
                        .append(posv).append(",")
                        .append(trv).append(",")
                        .append(tbloc).append(",")
                        .append(tlwloc).append(",")
                        .append(tcfloc).append(",")
                        .append(trwloc).append(",")
                        .append(tamloc).append(",")
                        .append(tcmloc).append(",")
                        .append(tdmloc).append(",")
                        .append(tlcbloc).append(",")
                        .append(trcbloc).append(",")
                        .append(tlfbloc).append(",")
                        .append(trfbloc).append(",")
                        .append(tgloc).append(",")
                        .append("\n");
            rn++;
            cursa.next();
        }

I am going to reconstruct the Writer and see if write(d) creates the same file as the StringBuilder.

The best way to do this would be with a StringBuilder then write that to the writer. E.g.

        StringBuilder csvString = new StringBuilder();
        for (r = 1; r < x; r++) {
            trecno = rn.toString();
            tname = currentRow.getString(1);
            // etc...
            csvString.append(trecno).append(",")
                     .append(tname).append(",")
                     // etc. for other entries
                     .append("\n");
            rn++;
        }
        String flname = new String("/" + namet + ".csv");
        FileSystemStorage fs = FileSystemStorage.getInstance();
        File sendFile = new File(fs.getAppHomePath() + flname);
        Util.writeStringToFile(sendFile, csvString.toString());