將大量數據下載至Excel

將大量數據下載至Excel，循環調用service釋放內存并用SXSSFWorkbook避免內存溢出。

/**
     * 画面结果导出按钮操作
     */
    public void exportResult() throws Exception {

        // Execl生成
        XSSFWorkbook workBook = new XSSFWorkbook();
        HttpServletRequest request = ServletActionContext.getRequest();
        String realPath = request.getSession().getServletContext()
                .getRealPath("/");

        OPCPackage opc = OPCPackage.open(realPath
                + PurchaseInvoice_Constants.PRODUCTLISTPATH);
        workBook = new XSSFWorkbook(opc);
        // 内存中保留 10000 条数据，以免内存溢出，其余写入硬盘
        SXSSFWorkbook sworkBook = new SXSSFWorkbook(workBook, 10000);
        Sheet nowSheet = sworkBook.getSheetAt(0);
        
        CellStyle style = sworkBook.createCellStyle();
        style.setBorderBottom(XSSFCellStyle.BORDER_THIN);
        style.setBorderLeft(XSSFCellStyle.BORDER_THIN);
        style.setBorderRight(XSSFCellStyle.BORDER_THIN);
        style.setBorderTop(XSSFCellStyle.BORDER_THIN);

        // 需要导出的数据取得
        int count = productListService.getExportResultListCount(searchDto);
        
        int sheetPage = 0;

        if(count % 50000 == 0){
         sheetPage = count / 50000;
        }else {
         sheetPage = count / 50000 + 1;
        }
        
        for (int sheet=0;sheet<sheetPage;sheet++) {
            searchDto.setStartPoint(sheet*50000);
            searchDto.setEndPoint(50000);
            
            List<ProductListExportDto> exportList = productListService.getExportResultList(searchDto);

            Row row = null;
            Cell cell = null;
            
            int i = 0;
            for (ProductListExportDto arg : exportList) {

                row = nowSheet.createRow(i+7+sheet*50000);
                
                // No
                cell = row.createCell(0);
                cell.setCellValue(String.valueOf(i+1));
                cell.setCellStyle(style);
                
                // 供应商简称
                cell = row.createCell(1);
                cell.setCellValue(arg.getSuppliershortName());
                cell.setCellStyle(style);