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);
        }
    }

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);
        }
    }

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 URL
        URL 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 content
            ByteBuffer buffer = ByteBuffer.allocateDirect(1024 << 2);

            // Read the file content into the byte buffer
            while (readableByteChannel.read(buffer) != -1) {
                // Prepare the byte buffer to be read again
                buffer.flip();
                while (buffer.hasRemaining()) {
                    writableByteChannel.write(buffer);
                }
                buffer.clear();
            }
        } catch (Exception e) {
            // Handle network or file IO exceptions here
            log.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