1、首先頁面請求不可以用ajax請求，否則會將資訊輸出到控制檯

var url = "${path}/pc/qrcode/downLoad.do?filename="+ 檔案路徑 +"&imgName=" +儲存的檔名稱;
window.location.href = url;

2、java程式碼

/**
	 * 下載圖片到本地
	 * @param request
	 * @param response
	 * @param filename 檔案路徑
	 * @param imgName 儲存的圖片名稱
	 */
	@RequestMapping("/pc/qrcode/downLoad.do")
	public void download(HttpServletRequest request, HttpServletResponse response,
			@RequestParam("filename") String filename, @RequestParam("imgName") String imgName){
		
		String path = request.getRealPath("");
		File file = new File(path+File.separator+filename);
		FileInputStream is = null;
         // 響應輸出流
        ServletOutputStream out = null;
        if(file.exists()) {
        	try {
           	response.setContentType("application/x-jpg");
           	//設定頭資訊,內容處理的方式,attachment以附件的形式開啟,就是進行下載,並設定下載檔案的命名
   			response.setHeader("Content-Disposition","attachment;filename=\""+URLEncoder.encode(imgName,"UTF-8")+".jpg\"");
   			response.setHeader("Content-Transfer-Encoding","binary");
   			response.setHeader("Cache-Control", "must-revalidate, post-check=0, pre-check=0");
   			response.setHeader("Pragma", "public");
   			response.flushBuffer();
           	is = new FileInputStream(file);
           	out = response.getOutputStream();
           	// 建立緩衝區
           	byte[] buffer = new byte[1024];
           	int len = 0;
   	        	while ((len = is.read(buffer)) != -1) {
   	        		out.write(buffer, 0, len);
   	        	}
   	        	is.close();
   	        	out.flush();
   	        	out.close();
            } catch (Exception e) {
            	log.error("ERROR:" + e);
            } finally {
            	try {
            		is.close();
            		out.flush();
   					out.close();
   				} catch (IOException e) {
   					e.printStackTrace();
   				}
            }
        } else {
        	log.info("下載的圖片不存在！");
        }
	}