java追加excel数据，内存溢出有关问题

FileOutputStream out=new FileOutputStream(path+fileName_exp,true);        //File wbook = new File(path+fileName_exp);        WritableWorkbook book = Workbook.createWorkbook(out);        WritableSheet sheet = book.createSheet("移动电话号段表数据", 0);        Label label = new Label(0, 0, "号段ID");        sheet.addCell(label);        label = new Label(1, 0, "号段低位");        sheet.addCell(label);        label = new Label(2, 0, "号段高位");        sheet.addCell(label);        label = new Label(3, 0, "号段归属地区号");        sheet.addCell(label);        label = new Label(4, 0, "运营商");        sheet.addCell(label);        label = new Label(5, 0, "生效时间");        sheet.addCell(label);        label = new Label(6, 0, "失效时间");        sheet.addCell(label);[color=#FF0000]for (int i=1000,j=1;i<count;j++) {                fileName = importSheet(hashSet.iterator(),fileName_exp,path,book,sheet,out,i*(j-1)+1);                                Workbook   newWorkBook   =   Workbook.getWorkbook(new File(path+fileName_exp));                 book = Workbook.createWorkbook(new File(path+fileName_exp), newWorkBook);                sheet = book.getSheet("移动电话号段表数据");            }[/color]//写入到excel中的函数public String importSheet(Iterator it,String fileName,String path,WritableWorkbook book,WritableSheet sheet,FileOutputStream out,int i) throws Exception{ //filename是生成文件的路径及用户名;it是内容, Iterator it;            try {            int row = i;                        for (; it.hasNext(); ) {                OcsProdCellMsisdn vo = (OcsProdCellMsisdn) it.next();                Label xm = new Label(0, row, vo.getMsisdnId());                sheet.addCell(xm);                Label username = new Label(1, row, vo.getMsisdnFirst());                sheet.addCell(username);                Label pwd = new Label(2, row, vo.getMsisdnLast());                sheet.addCell(pwd);                 pwd = new Label(3, row, vo.getAreaCode());                sheet.addCell(pwd);                 pwd = new Label(4, row, vo.getOperatorCode());                sheet.addCell(pwd);                 pwd = new Label(5, row, vo.getEffDate());                sheet.addCell(pwd);                pwd = new Label(6, row, vo.getExpDate());                sheet.addCell(pwd);                row++;            }            book.write();            book.close();            out.flush();            //out.close();        } catch (Exception e) {            e.printStackTrace();        }        return fileName;    }