java 通过远程URL实现文件下载几种方式

文章目录

• • 概要
  • 需要具备参数
  • 实现的四种方式：
  • 小结

    概要

    java环境下通过远程接口实现文件下载几种方式：

    
    （图片来源网络，侵删）
    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 
                    // 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);
        }
    
            // 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)));
        }