使用spring框架ResponseEntity實現檔案下載

@RequestMapping("downLoad")
public ResponseEntity<byte[]> downloadPromisePdf() {
  String fileName = "企業誠信守法承諾書.pdf";
  try {
    byte[] pdf = **;//byte檔案
    String dfileName = new String(fileName.getBytes("gb2312"), "iso8859-1");
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
    headers.setContentDispositionFormData("attachment", dfileName);
    return new ResponseEntity<>(pdf, headers, HttpStatus.OK);
  } catch (BuzEx e){
    logger.error( e.getMessage());
  }catch (Exception e) {
  }
  return null;
}

//獲得檔案陣列ids後 迴圈下載方法
$.each(ids,function(i,value){    	
   	downLoad(fileFunctionPathArray[i],fileNameInServerArray[i],fileOriginalNameArray[i],ids[i]);
    })
//下載方法
function downLoad(fileFunctionPath,fileNameInServer,fileOriginalName,ids){
            $.ajax({
            	//檢查檔案是否存在
                url: "/ResourceManage/resourceDownloaduserLink/checkPermission",
                data: {
                    sysuserid: localStorage.getItem("id"),
                    resourceid: ids
                },
                success: function (data) {//檔案存在則建立動態a標籤批次下載檔案
                    if (data.success) {
                    //ResponseEntity下載檔案的url
                    	var url = "../filehandle/downLoad.do?filePlatPath=" 
                        	+ "resource&fileFunctionPath=" + fileFunctionPath 
                        	+ "&fileNameInServer=" + fileNameInServer
                        	+ "&fileOriginalName=" + fileOriginalName;
                    	var fileName = fileNameInServer;
                    	
                    	downloadFile(url,fileName);//動態建立a標籤 批次下載
                    }
                }
            })
        }
		//動態建立a標籤
        const downloadFile = (url, fileName = '') => {
  		  let eleLink = document.createElement('a');
  		  eleLink.download = fileName;
  		  eleLink.style.display = 'none';
  		  eleLink.href = url;
  		  // 受瀏覽器安全策略的因素，動態建立的元素必須新增到瀏覽器後才能實施點選
  		  document.body.appendChild(eleLink);
  		  // 觸發點選  
  		  eleLink.click();
  		  // 然後移除
  		  document.body.removeChild(eleLink);
  		};