1.  MySQL

 1     public void getFile(String id,HttpServletResponse response) {
 2         // TODO 自动生成的方法存根
 3         DataObject criteria = DataFactory.INSTANCE.create("com.primeton.das.criteria", "criteriaType");
 4         criteria.set("_entity", "com.primeton.eos.auditManager.audit.service.audit.AuditFiles");
 5         criteria.set("_expr[1]/fileId", id);
 6         DataObject[] datas = DatabaseUtil.queryEntitiesByCriteriaEntity("default", criteria,0,1);
 7         if(datas.length > 0) {
 8             String fileName = datas[0].getString("fileName");
 9             response.reset(); // 清除buffer缓存
10             response.setCharacterEncoding("UTF-8");
11             try {
12                 response.addHeader("Content-Disposition",String.format("attachment; filename=\"%s\"", URLEncoder.encode(fileName, "utf-8")));
13 //datas[0]    取出当前的实体信息，getBytes为返回byte数组数据，塞进response中返回给前台    response.getOutputStream().write(datas[0].getBytes("content"));
14             } catch (IOException e) {
15                 // TODO 自动生成的 catch 块
16                 e.printStackTrace();
17             }
18         }
19     }

　　　　2.  MongoDB

 1     public void getFile(String id, HttpServletResponse response) {
 2         GridFS gridFs = new GridFS(MongodbUtil.getDB(), "files");
 3         GridFSDBFile gfsfile = gridFs.findOne(new BasicDBObject("_id", id));
 4         if (gfsfile == null) {
 5             return;
 6         }
 7         String fileName = gfsfile.getFilename().replace(",", "");
 8         response.reset(); // 清除buffer缓存
 9         response.setCharacterEncoding("UTF-8");
10         response.setContentType(gfsfile.getContentType());
11         try {
12             response.setContentType("application/x-download");
13             response.addHeader("Content-Disposition",String.format("attachment; filename=\"%s\"", URLEncoder.encode(fileName, "utf-8")));
14 //将文件数据流塞进response中
15             gfsfile.writeTo(response.getOutputStream());
16         } catch (IOException e) {
17             // TODO 自动生成的 catch 块
18             e.printStackTrace();
19         }
20     }

　　　　3.  OSS

 1 //END_POIND, ACCESS_KEY_ID,ACCESS_KEY_SECRET，BUCKET_NAME为OSS第三方提供的唯一串    
 2 public void getFile(String id, HttpServletResponse response) {
 3         
 4             OSS ossClient = null;
 5             try {
 6                 ossClient = new OSSClientBuilder().build(END_POIND, ACCESS_KEY_ID,ACCESS_KEY_SECRET);
 7                 OSSObject ossObject = ossClient.getObject(BUCKET_NAME, id);
 8                 response.reset(); // 清除buffer缓存
 9                 response.setCharacterEncoding("UTF-8");
10                 response.addHeader("Content-Disposition",String.format("attachment; filename=\"%s\"", URLEncoder.encode("文件", "utf-8")));
11                 response.getOutputStream().write(toByteArray(ossObject.getObjectContent()));
12                 ossObject.close();
13             } catch (Exception e) {
14                 log.error("文件下载发生异常错误",e);
15                 return;
16             }finally {
17                 if(ossClient!=null) {
18                     ossClient.shutdown();
19                 }
20             
21         }
22     }
23 //文件流转byte数组
24     private byte[] toByteArray(InputStream input) throws IOException {
25         ByteArrayOutputStream output = new ByteArrayOutputStream();
26         byte[] buffer = new byte[1024 * 4];
27         int n = 0;
28         while (-1 != (n = input.read(buffer))) {
29             output.write(buffer, 0, n);
30         }
31         return output.toByteArray();
32     }