java 批量下载文件(开发笔记)-优快云博客

本文介绍了一种在Java中实现的文献批量下载及压缩的方法。该方法能够根据用户选择，下载单个或多个文献，当下载多个文献时，将它们压缩成一个.zip文件。代码利用了Spring框架的ResponseEntity与InputStreamResource，以及MongoDB的GridFS进行文件存储与检索。

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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;

   }