java 通过远程URL实现文件下载几种方式

概要

java环境下通过远程接口实现文件下载几种方式：

1. 使用NIO下载文件， 需要 jdk 1.7+
2. 利用 commonio 库下载文件，依赖Apache Common IO
3. 文件通道FileChahhel
4. 通过URL直接下载转换成MultipartFile
5. 接口服务直接返回文件流

需要具备参数

1. 文件内容
2. 保存地址
3. 文件名称类型（后缀）

实现的四种方式：

使用NIO下载文件

/*** 使用NIO下载文件， 需要 jdk 1.7+* @param url 下载地址* @param saveDir 保存地址* @param fileName 文件名称*/public static void downloadByNIO(String url, String saveDir, String fileName) {try (InputStream ins = new UrlResource(url).getInputStream()) {Path target = Paths.get(saveDir, fileName);Files.createDirectories(target.getParent());Files.copy(ins, target, StandardCopyOption.REPLACE_EXISTING);} catch (IOException e) {log.error("文件下载失败：" + e.getMessage());throw new RuntimeException("downloadByNIO error from remoteUrl", e);}}

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利用Apache common io 库下载文件

    /*** 利用 commonio 库下载文件，依赖Apache Common IO* @param url 下载地址* @param saveDir 保存地址* @param fileName 文件名称*/public static void downloadByApacheCommonIO(String url, String saveDir, String fileName) {try {FileUtils.copyURLToFile(new URL(url), new File(saveDir, fileName));} catch (IOException e) {log.error("文件下载失败：" + e.getMessage());throw new RuntimeException("downloadByApacheCommonIO error from remoteUrl", e);}}

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使用文件通道FileChahhel下载文件

/*** 文件下载* 使用文件通道FileChahhel下载文件* @param downloadUrl 下载地址*/public static void downloadFileByChannel(String downloadUrl, String tempPath) {ReadableByteChannel readableByteChannel;FileUtil.createTempFile(new File(tempPath));try (FileChannel fileChannel = new FileOutputStream(FileUtil.createTempFile(new File(tempPath))).getChannel()){URL url = new URL(downloadUrl);readableByteChannel = Channels.newChannel(new BufferedInputStream(url.openStream()));fileChannel.transferFrom(readableByteChannel, 0, Long.MAX_VALUE);} catch (Exception e) {log.error("文件下载失败：" + e.getMessage());throw new RuntimeException("downloadFileByChannel error from downloadUrl", e);}}

通过URL直接转换成MutipartFile

public static MultipartFile getFileFromUrl(String url, String fileName) throws IOException {// Create a resource from the URLURL urlObj = new URL(url);HttpURLConnection connection = (HttpURLConnection) urlObj.openConnection();connection.setRequestMethod("GET");connection.setConnectTimeout(10000);connection.setReadTimeout(60000);connection.setDoOutput(true);DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();DiskFileItem fileItem = (DiskFileItem) fileItemFactory.createItem("file",MediaType.ALL_VALUE, true, fileName);fileItem.getOutputStream().flush();try (ReadableByteChannel readableByteChannel = Channels.newChannel(connection.getInputStream());OutputStream outputStream = fileItem.getOutputStream();WritableByteChannel writableByteChannel = Channels.newChannel(outputStream)) {// Create a byte buffer to store the file contentByteBuffer buffer = ByteBuffer.allocateDirect(1024 << 2);// Read the file content into the byte bufferwhile (readableByteChannel.read(buffer) != -1) {// Prepare the byte buffer to be read againbuffer.flip();while (buffer.hasRemaining()) {writableByteChannel.write(buffer);}buffer.clear();}} catch (Exception e) {// Handle network or file IO exceptions herelog.error("Error uploading file", e);throw e;}return new CommonsMultipartFile(fileItem);}

接口服务直接返回文件流

	@PostMapping("/download")public ResponseEntity<InputStreamResource> downloadFile(String url) throws IOException {// 从远程地址下载文件流URL remoteUrl = new URL(url);URLConnection connection = remoteUrl.openConnection();ReadableByteChannel readableByteChannel = Channels.newChannel(connection.getInputStream());// 设置响应头信息HttpHeaders headers = new HttpHeaders();headers.add("Content-Disposition", "attachment; filename=" + url.substring(url.lastIndexOf("/") + 1));MediaType mediaType = ObjectUtils.defaultIfNull(MediaType.parseMediaType(connection.getContentType()), MediaType.APPLICATION_OCTET_STREAM);// 返回文件流给请求端return ResponseEntity.ok().headers(headers).contentType(mediaType).body(new InputStreamResource(Channels.newInputStream(readableByteChannel)));}

小结

这里没有小洁