實現檔案的下載功能，下載excel檔案
兩種實現方式
一：下載本地指定路徑下的指定檔案。

前端程式碼：

<a id="download1" type="hidden" style='color:red' href='填寫後臺指定coltroller-方法的地址'>&nbsp;&nbsp;下載資料</a>

Controller層程式碼：

@RequestMapping("download")    
    @ResponseBody
    public ResponseEntity<byte[]> download() throws
 
 IOException {

        ResponseEntity<byte[]> a = null;
        try {
            a = tranddelService.downloadExcel();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return  a;
    }

ServiceImpl實現類方法：

public ResponseEntity<byte[]> downloadExcel() throws
 
 Exception{
        //下載檔名稱-下載後文件的名稱+字尾
        String name = "資料.xls";
        //要下載檔案的路徑
        String route = Utils.getRequest().getSession().getServletContext().getRealPath("/")+"file/qs/error/error.xls";
        //根據路徑建立file
        File file=new File(route);  //存放太那些好的excel的絕對路徑
        HttpHeaders headers = new
 
 HttpHeaders();    
        String fileName=new String(name.getBytes("UTF-8"),"iso-8859-1");//為了解決中文名稱亂碼問題  
        headers.setContentDispositionFormData("attachment", fileName);   
        headers.setContentType(MediaType.APPLICATION_OCTET_STREAM); 
        return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file), headers, HttpStatus.CREATED);
    }

Tip：
Utils.getRequest()為獲取request的方法，自己重寫的。

二：設定模板路徑，填充模板資訊，下載。

設定模板下載和按照路徑下載在實現層有區別

public ResponseEntity<byte[]> downloadExcel() throws Exception{
        ExcelPoi excelPoi = new ExcelPoi();
        /* 個入檔案資料的業務
        Map<String , String> map = new HashMap<String, String>();
        //轉date格式
        Date today = DateUtil.strToDate(date);
        //昨天的 yyyy-MM-dd
        String Yesterday = DateUtil.get4yMd(DateUtil.getNextDay1(today));
        //前天 yyyy-MM-dd
        String TWOYesterday = DateUtil.get4yMd(DateUtil.getNextDay2(today));
        map.put("Yesterday", Yesterday);
        map.put("TWOYesterday", TWOYesterday);
        List<Map<String, Object>> list = bankbilldataDao.getList("getBnoFile", map);*/
        //拼接寫入excel檔案的那個資料格式
        List<String[]> li = retExcelStr(list);
        String filePath = excelPoi.writer(date, li);
        String name = filePath.substring(filePath.length()-19,filePath.length());
        File file=new File(filePath);
        HttpHeaders headers = new HttpHeaders();    
        String fileName=new String(name.getBytes("UTF-8"),"iso-8859-1");//為了解決中文名稱亂碼問題  
        headers.setContentDispositionFormData("attachment", fileName);   
        headers.setContentType(MediaType.APPLICATION_OCTET_STREAM); 
        return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file),    
                headers, HttpStatus.CREATED);
}
    //方法的作用：寫入檔案提出的公用類，會呼叫公用類，需要傳進去List<String[]>型別的資料寫入。String[]資料的順序就是一行的從左到右順序
    public List<String[]> retExcelStr(List<Map<String, Object>> list){
        List<String[]> retList = new ArrayList<String[]>(); 
        StringBuilder stringBuilder = new StringBuilder();
        if(list.size() > 0){ 
            for (int i = 0;i < list.size();i++){
                String bno = (String) list.get(i).get("BNO");
                stringBuilder.append(bno).append(",");
            }
            String[] retStrArray = stringBuilder.substring(0,stringBuilder.length()-1).split(",");
            retList.add(retStrArray);
        }
        return retList;
    }

Tip：
excelPoi.writer(date, li);

public  String writer(String date,List<String[]> list) {  
          try {
                Workbook wb = null;  
                wb = new XSSFWorkbook( new FileInputStream(getRequest().getSession().getServletContext().getRealPath("/")+"mode/qsMode.xlsx"));  
                Sheet sheet1=wb.getSheetAt(0);
                if(list.size()>0){
                     for(int i=0;i<list.get(0).length;i++){
                        Row row = (Row) sheet1.createRow(i+1);  
                         Cell cell = row.createCell(0);  
                         cell.setCellValue(list.get(0)[i]);  
                    }
                }
                new File(getRequest().getSession().getServletContext().getRealPath("/")+"file/qs/"+new SimpleDateFormat("yyyyMMdd").format(new Date())).mkdirs();
                f = getRequest().getSession().getServletContext().getRealPath("/")+"file/qs/"+new SimpleDateFormat("yyyyMMdd").format(new Date())+"/"+date+"商編檔案.xlsx";
                OutputStream stream= new FileOutputStream(f);
                wb.write(stream);  
                stream.close();  
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }  
        return f;
        }

模板為：qsMode.xlsx檔案，只有第一列有頭資訊，只寫入第一列的值