请问下 为什么 jxl 怎么能只能插入一行数据

我想把ACCESS里的数据导入到excel里面但是插入后只有一行显示在excel里面。
try
        {
            c = DriverManager.getConnection( "jdbc:odbc:students", "","" );
            sq1 = c.createStatement();
            rs = sq1.executeQuery("select * from stu" );
            int index=0;
            WritableWorkbook book;
            try {
                book = Workbook.createWorkbook(new File("e:/atoecel.xls"));
                WritableSheet sheet = book.createSheet("Sheet_1", 0);                while (rs.next())
                {
                    s1 = rs.getString(1);
                    s2 = rs.getString(2);
                    s3 = rs.getString(3);
                    s4 = rs.getString(4);
                    Label label1 = new Label (0,index,s1);
                    sheet.addCell(label1);
                    Label label2 = new Label (1,index,s2);
                    sheet.addCell(label2);
                    Label label3 = new Label (2,index,s3);
                    sheet.addCell(label3);
                    Label label4 = new Label (3,index,s4);
                    sheet.addCell(label4);
                    book.write();
                    index++;
                }
                c.close();
                book.close();
            }
            catch (Exception e)
            {
            }
        }
        catch (Exception ex)
        {
            
        }
请大家指教，谢谢