FileUtils （從磁盤下載，從網絡下載）

public class FileUtils {

    /**
     * realPath 磁盤路徑 D://project/download/
     * urlPath 后半部分路徑 具體根據業務需求，例如：WEB-INF/download.xlsx
     * downLoadName 下載后的新名字
     * @param request
     * @param resp
     */
    public static void downloadFromDisk(HttpServletRequest request, HttpServletResponse resp,String realPath,String urlPath,String downLoadName) {
        //文件最終路徑,例如：D://project/download/WEB-INF/download.xlsx
        String path = realPath + File.separator + urlPath;
        File file = new File(path);
        if(!file.exists()){
            System.out.println("---------<系統找不到指定的文件>---------");
            return;
        }
        resp.reset();
        resp.setContentType("application/octet-stream");
        resp.setCharacterEncoding("utf-8");
        resp.setContentLength((int) file.length());
        //下載到本地的文件名，例如：abc.xlsx(注意：這里跟路徑中的文件名區分開)
        String downloadName = downLoadName;
        resp.setHeader("Content-Disposition", "attachment;filename=" + downloadName );
        byte[] buff = new byte[1024];
        BufferedInputStream bis = null;
        OutputStream os = null;
        try {
            os = resp.getOutputStream();
            bis = new BufferedInputStream(new FileInputStream(file));
            int i = 0;
            while ((i = bis.read(buff)) != -1) {
                os.write(buff, 0, i);
                os.flush();
            }
            System.out.println("---------<文件下載成功>---------");
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                bis.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static void downloadFromIntNet(String urlStr, String fileName, String savePath) throws IOException {
        URL url = new URL(urlStr);
        HttpURLConnection conn = (HttpURLConnection)url.openConnection();
        //設置超時間為5秒
        conn.setConnectTimeout(5*1000);
        //防止屏蔽程序抓取而返回403錯誤
        conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");
        //得到輸入流
        InputStream inputStream = conn.getInputStream();
        //創建保存路徑
        File saveDir = new File(savePath);
        if(!saveDir.exists()) {
            saveDir.mkdir();
        }
        //創建文件
        File file = new File(saveDir+File.separator+fileName);
        //文件輸出流
        FileOutputStream fout = new FileOutputStream(file);
        //輸出文件
        byte[] buff = new byte[4096];
        int len = -1;
        while ((len = inputStream.read(buff)) != -1) {
            fout.write(buff,0,len);
        }
        //關閉輸出輸入流
        fout.close();
        inputStream.close();
        System.out.println("info:"+url+" download success");
    }

}


----------------------------------調用---------------------------------------

/*從磁盤下載*/
String realPath = "C:\\files\\images";
String urlPath = "user.png";
String downLoadName = "newname.png";
FileUtils.downloadFromDisk(request,resp,realPath,urlPath,downLoadName);

/*從網絡下載*/
String path = "http://yourIP:yourPort/files/201111/images/2019/12/24/2019122409504998593372629015.jpg";
FileUtils.downloadFromIntNet(path,"test.jpg","C:\\myfile\\images");