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java实现文件下载的几种方法，小白们收藏这篇就足够了

news 2026/7/5 13:09:43

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(); } }

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

/** * 将文件转为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

/** * 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(); } } }

七、项目实战

FileInputStream fileInputStream = new FileInputStream("C:/Users/Admin/Downloads/test.docx"); response.reset(); response.setContentType("application/octet-stream"); String resultFileName = URLEncoder.encode("test" + task_id + ".docx", "UTF-8"); response.setHeader("Content-disposition", "attachment;filename=" + resultFileName + ";" + "filename*=utf-8''" + resultFileName); //URLConnection conn = url.openConnection(); //InputStream inStream = conn.getInputStream(); // 循环取出流中的数据 byte[] b = new byte[100]; int len; try { while ((len = fileInputStream.read(b)) > 0) response.getOutputStream().write(b, 0, len); fileInputStream.close(); } catch (IOException e) { e.printStackTrace(); } response.flushBuffer();

最终成功将文件下载下来了。

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