java 批量下载文件(开发笔记)

本是古典何须时尚 2022-05-16 12:43 675阅读 0赞

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<InputStreamResource> 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<FullTextLibrary> iter = fullTextLibraryRepository.findAll(predicate);
    		int total = 0;
    		String fileName = "";
    		Collection<String> fileIds = new ArrayList<String>();
    	
    		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<GridFSDBFile> 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。