Java如何实现下载文件的几种方式

目录

• • 一、以流的方式下载
  • 二、下载本地文件
  • 三、下载网络文件
  • 四、在线打开的方式
  • 五、将文件转换成base64
  • 六、将MultipartFile转换为File

一、以流的方式下载

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;    }

二、下载本地文件

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();        }    }

三、下载网络文件

public void downloadNet(HttpServletResponse response) throws MalfORMedURLException {        // 下载网络文件        int bytesum = 0;        int byteread = 0;        URL url = new URL("windine.blogdriver.com/loGo.gif");        try {            URLConnection conn = url.openConnection();            InputStream inStream = conn.getInputStream();            FileOutputStream fs = new FileOutputStream("c:/abc.gif");            byte[] buffer = new byte[1204];            int length;            while ((byteread = inStream.read(buffer)) != -1) {                bytesum += byteread;                System.out.println(bytesum);                fs.write(buffer, 0, byteread);            }        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }

public void downLoadFile(HttpServletResponse response, String httpUrl) {        ServletOutputStream out = null;        try {            //与服务器建立连接            URL url = new URL(httpUrl);            URLConnection conn = url.openConnection();            InputStream inputStream = conn.getInputStream();            try {                //1.设置文件ContentType类型，这样设置，会自动判断下载文件类型                response.setContentType("multipart/form-data");            } catch (Exception e){                e.printStackTrace();            }            out = response.getOutputStream();            // 读取文件流            int len = 0;            byte[] buffer = new byte[1024 * 10];            while ((len = inputStream.read(buffer)) != -1) {                out.write(buffer, 0, len);            }            out.flush();            out.close();            inputStream.close();        } catch (Exception e){            e.printStackTrace();        }    }

四、在线打开的方式

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[1024];        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();    }

五、将文件转换成base64

    public static String getBase64FromFile(File file) throws IOException {        FileInputStream in = null;        ByteArrayOutputStream out = null;        try {            in = new FileInputStream(file);            out = new ByteArrayOutputStream();            int read = 0;            byte[] buffer = new byte[1024];            while ((read = in.read(buffer, 0, 1024)) != -1) {                out.write(buffer, 0, read);            }             return Base64.getEncoder().encodeToString(out.toByteArray());        } catch (IOException e) {            throw e;        } finally {            if (in != null) {                in.close();            }            if (out != null){                out.close();            }        }    }

六、将MultipartFile转换为File

        public static File MultipartFileToFile(MultipartFile multiFile) throws IOException {        String fileName = multiFile.getOriginalFilename();        String prefix = fileName.substring(fileName.lastIndexOf("."));        InputStream in = null;        OutputStream out = null;        try {            File file = File.createTempFile(fileName, prefix);            out = new FileOutputStream(file);            in = multiFile.getInputStream();            int read = 0;            byte[] buffer = new byte[1024];            while ((read = in.read(buffer, 0, 1024)) != -1) {                out.write(buffer, 0, read);            }             return file;        } catch (Exception e) {            throw e;        }finally {            if (in != null){                in.close();            }            if (out != null){                out.close();            }        }    }

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