Java实现文件下载功能

Java文件下载的几种方式

public class FileDownloadUtil {

    public HttpServletResponse download(String path, HttpServletResponse response) {
        try {
            // path是指欲下载的文件的路径。
            File file = new File(path);
            // 取得文件名。
            String filename = file.getName();
            // 取得文件的后缀名。
            String ext = filename.substring(filename.lastIndexOf(".") + 1).toUpperCase();

            // 以流的形式下载文件。
            InputStream fis = new BufferedInputStream(new FileInputStream(path));
            byte[] buffer = new byte[fis.available()];
            fis.read(buffer);
            fis.close();
            // 清空response
            response.reset();
            // 设置response的Header
            response.addHeader("Content-Disposition", "attachment;filename=" + new String(filename.getBytes()));
            response.addHeader("Content-Length", "" + file.length());
            OutputStream toClient = new BufferedOutputStream(response.getOutputStream());
            response.setContentType("application/octet-stream");
            toClient.write(buffer);
            toClient.flush();
            toClient.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return response;
    }

    public void downloadLocal(HttpServletResponse response) throws FileNotFoundException {
        // 下载本地文件
        String fileName = "Operator.doc".toString(); // 文件的默认保存名
        // 读到流中
        InputStream inStream = new FileInputStream("c:/Operator.doc");// 文件的存放路径
        // 设置输出的格式
        response.reset();
        response.setContentType("bin");
        response.addHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
        // 循环取出流中的数据
        byte[] b = new byte[100];
        int len;
        try {
            while ((len = inStream.read(b)) > 0){
                response.getOutputStream().write(b, 0, len);
            }
            inStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void downloadNet(HttpServletResponse response) {
        // 下载网络文件
        int bytesum = 0;
        int byteread = 0;

        try {
            String fileUrl = "http://oss.aliyun.cn/pro/2021/06/30/2635a51b-3338-478c-9e46-0e7834afabbb.gif";
            URL url = new URL(fileUrl);
            URLConnection conn = url.openConnection();
            InputStream inStream = conn.getInputStream();
            FileOutputStream fs = new FileOutputStream("c:/abc.gif");

            byte[] buffer = new byte[8192];
            int length;
            while ((byteread = inStream.read(buffer)) != -1) {
                bytesum += byteread;
                System.out.println(bytesum);
                fs.write(buffer, 0, byteread);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

支持在线打开文件的一种方式

public class FileDownloadUtil {

    /**
     * 支持在线打开文件的一种方式
     * @param filePath
     * @param response
     * @param isOnLine
     * @throws Exception
     */
    public void downLoad(String filePath, HttpServletResponse response, boolean isOnLine) throws Exception {
        File f = new File(filePath);
        if (!f.exists()) {
            response.sendError(404, "File not found!");
            return;
        }
        BufferedInputStream br = new BufferedInputStream(new FileInputStream(f));
        byte[] buf = new byte[8192];
        int len = 0;

        response.reset(); // 非常重要
        if (isOnLine) { // 在线打开方式
            URL u = new URL("file:///" + filePath);
            response.setContentType(u.openConnection().getContentType());
            response.setHeader("Content-Disposition", "inline; filename=" + f.getName());
            // 文件名应该编码成UTF-8
        } else { // 纯下载方式
            response.setContentType("application/x-msdownload");
            response.setHeader("Content-Disposition", "attachment; filename=" + f.getName());
        }
        OutputStream out = response.getOutputStream();
        while ((len = br.read(buf)) > 0){
            out.write(buf, 0, len);
        }
        br.close();
        out.close();
    }
}

网络url下载，并写入浏览器

public class FileDownloadUtil {

    /**
     * 网络url下载
     * @param request
     * @param response
     */
    public void downloadFileURL(HttpServletRequest request, HttpServletResponse response) {
        String fileUrl = "http://oss.aliyun.cn/pro/2021/06/30/2635a51b-3338-478c-9e46-0e7834afabbb.pdf";
        try {
            URL url = new URL(fileUrl);
            URLConnection conn = url.openConnection();
            InputStream inStream = conn.getInputStream();
            //对文件名进行编码防止中文乱码
            String filename = FileDownloadUtil.encodeDownloadFilename("文件.pdf", request);
            response.setContentType("application/x-msdownload");
            response.setHeader("Content-Disposition", "attachment; filename=" + filename);

            OutputStream out = response.getOutputStream();

            byte[] buffer = new byte[8192];
            int length;
            while ((length = inStream.read(buffer)) != -1) {
                out.write(buffer, 0, length);
            }
            inStream.close();
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

public class FileDownloadUtil {

    /**
     * 下载文件时，针对不同浏览器，进行附件名的编码
     *
     * @param filename 载文件名
     * @param request 请求request
     * @return 编码后的下载附件名
     * @throws IOException
     */
    public static String encodeDownloadFilename(String filename, HttpServletRequest request)
            throws IOException {
        String agent = request.getHeader("user-agent");//获得游览器
        if (agent.contains("Firefox")) { // 火狐浏览器
            filename = "=?UTF-8?B?"
                    + Base64.getEncoder().encode(filename.getBytes("utf-8"))
                    + "?=";
            filename = filename.replaceAll("\r\n", "");
        } else { // IE及其他浏览器
            filename = URLEncoder.encode(filename, "utf-8");
            filename = filename.replace("+"," ");
        }
        return filename;
    }
}

参考：
https://www.cnblogs.com/ungshow/archive/2009/01/12/1374491.html