java 批量下载文件(开发笔记)

需求：

 下载文件，选择单个文档则下载单个文档，选择多个文档则讲多个文档压缩进一个压缩文件。

 

	public ResponseEntity downloadFiles(String literIds,String type) throws YMLibWebApplicationException {
		Assert.notNull(literIds, "未指定要下载的文献");
		if(null==type){
			type="";
		}
		String[] ids = literIds.split(",");
		HttpHeaders headers = new HttpHeaders();
		headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
		QFullTextLibrary qfullTextLibrary = QFullTextLibrary.fullTextLibrary;
		Predicate predicate = qfullTextLibrary.id.in(ids);
		Iterable iter = fullTextLibraryRepository.findAll(predicate);
		int total = 0;
		String fileName = "";
		Collection fileIds = new ArrayList();
	
		for (FullTextLibrary one : iter) {
			
			String fileId = one.getFileId();
			if (fileId != null && !fileId.equals("")) {
							
				fileIds.add(fileId);
				
				total++;
			}
			
			
		}
		if (total > 1) {
			fileName = DateUtils.date2String("yyyymmdd") + ".zip";
		}
		headers.setContentDispositionFormData("attachment", URLEncoder.encode(fileName));
		long length = 0L;

		Criteria cr = Criteria.where("_id").in(fileIds);
		Query query = new Query(cr);
		List files = gridFsOps.find(query);
		if (!files.isEmpty()) {
			if (files.size() == 1) {
				GridFSDBFile file = files.get(0);
				length = file.getLength();
				return ResponseEntity.ok().contentLength(length).contentType(MediaType.APPLICATION_OCTET_STREAM)
						.cacheControl(CacheControl.maxAge(3600, TimeUnit.SECONDS)).headers(headers)
						.body(new InputStreamResource(file.getInputStream()));

			} else {
					long statr_time=System.currentTimeMillis();
				try {
					String zipfilePath = zipFilePath + fileName;
					FileOutputStream outputStream = new FileOutputStream(zipfilePath);
					ZipOutputStream zipOut = new ZipOutputStream(new BufferedOutputStream(outputStream));
					// zipOut.putNextEntry(new ZipEntry("/"));
					for (GridFSDBFile file : files) {
						length += file.getLength();
						InputStream in = file.getInputStream();
						String file_id=file.getId().toString();
						zipOut.putNextEntry(new ZipEntry(file.getName()));
						int j = 0;
						byte[] buffer = new byte[1024*1024];
						while ((j = in.read(buffer)) > 0) {
							zipOut.write(buffer, 0, j);
						}
						// 关闭输入流
						in.close();
					}
					zipOut.closeEntry();
					zipOut.flush();
					zipOut.close();
					// 文件压缩成功
					FileInputStream inputStream = new FileInputStream(zipfilePath);
					
					long end_time=System.currentTimeMillis();
					System.out.println(end_time-statr_time);
					return ResponseEntity.ok().contentLength(length).contentType(MediaType.APPLICATION_OCTET_STREAM)
							.headers(headers)
							.body(new InputStreamResource(inputStream));

				} catch (Exception e) {
					log.error("压缩文件出错", e);
				}
			}
		}

		return null;

	}

 

文件通过mongoid 去mongofs里面拿，拿出来后判断文件的个数，多个文件则进行压缩。代码如上图。