Java Mongodb GirdFS/GridFSBucket下载文件操作

方法1：采用GridFSBucket对象进行下载，请看下方

 /**
     * 下载导出文件到服务器（新方法）
     * @param mac
     * @param filenames 文件名称集合
     * @param uploadpath 文件所在得绝对路径
     * @return
     */
    public static boolean downFilesByNames(MongoAttachConnect mac, Set filenames, String uploadpath){

        if(uploadpath == null || uploadpath.isEmpty())
        {
            return false;
        }
        else if(!uploadpath.endsWith("\\")){
            uploadpath += "\\";
        }

        MongoClient mongoClient = MongoClientBuild.GetMongoAttachClient(mac);

        MongoDatabase database = mongoClient.getDatabase(mac.BaseName);

        GridFSBucket gridFSBucket = GridFSBuckets.create(database);

        String finalDownpath = uploadpath;

        //根据文件名下载，指定下载版本，默认下载最新版本
        GridFSDownloadOptions downloadOptions = new GridFSDownloadOptions().revision(0);

        filenames.forEach(name->{

            FileOutputStream streamToDownloadTo = null;
            try {

                streamToDownloadTo = new FileOutputStream(finalDownpath+name);
                //根据文件名 下载文件
                gridFSBucket.downloadToStream(name, streamToDownloadTo, downloadOptions);
                streamToDownloadTo.close();
            } catch (IOException e) {
                e.printStackTrace();
            }

        });

        return true;
    }

方法2：采用GridFS对象进行下载操作：

 /**
     * 下载导出文件到服务器（老方法）
     * @param mac
     * @param filenames
     * @param downpath
     * @return
     */
    public static boolean downFilesByNames(MongoAttachConnect mac, Set filenames, String downpath){

        if(downpath == null || downpath.isEmpty())
        {
           return false;
        }
        else if(!downpath.endsWith("\\")){
            downpath += "\\";
        }

        MongoClient mongoClient = MongoClientBuild.GetMongoAttachClient(mac);

        //高版本驱动会提示方法已过期，不推荐使用
        DB db = mongoClient.getDB(mac.BaseName);

        GridFS fs = new GridFS(db);

        String finalDownpath = downpath;

        filenames.forEach(name->{

            GridFSDBFile one = fs.findOne(name);
            try {
                one.writeTo(finalDownpath +name);
            } catch (IOException e) {
                e.printStackTrace();
            }

        });

        return true;
    }