上传有两种方式，一种是使用UploadFromStream，另外一种是OpenUploadStream方式，这里使用的是第二种方式：

    public ObjectId save(){GridFSBucket gfsbk = GridFSBuckets.create(db, "user_photo");byte[] data = "Data to upload into GridFS".getBytes(StandardCharsets.UTF_8);GridFSUploadStream uploadStream = gfsbk .openUploadStream("user_09734");uploadStream.write(data);ObjectId id = uploadStream.getFileId();uploadStream.close();return id;}

解析:
1. GridFSBucket gfsbk = GridFSBuckets.create(db, “user_photo”);

创建一个容器，传入一个`MongoDatabase`类实例db，和容器名称"user_photo"作为参数   

2. GridFSUploadStream uploadStream = gfsbk .openUploadStream(“user_09734”);

打开上传流，传入一个String参数作为GirdFS文件的文件名

3. ObjectId id = uploadStream.getFileId();

得到刚刚上传的文件的id

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Mongo Java驱动GirdFS上传参考资料
下面是我编写的上传帮助类：

package com.huanle.utils.db;import java.io.ByteArrayOutputStream;
import java.io.IOException;import org.bson.types.ObjectId;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;import com.huanle.utils.model.FileEntity;
import com.mongodb.Block;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.gridfs.GridFSBucket;
import com.mongodb.client.gridfs.GridFSBuckets;
import com.mongodb.client.gridfs.GridFSUploadStream;
import com.mongodb.client.gridfs.model.GridFSFile;
import com.mongodb.gridfs.GridFS;@Component
public class GirdFSHelper {private GridFSBucket gfsbk;private MongoDatabase db;@Autowiredpublic GirdFSHelper(MongoDBHelper mongoManager){this.db = mongoManager.getDB("huanle");}/**保存文件到GirdFS,通过openUploadStream方式* @param bucket 容器名称* @param file 文件实体* @return 返回FileEntity*/public FileEntity save(String bucket,FileEntity file){gfsbk = GridFSBuckets.create(db, bucket);GridFSUploadStream uploadStream = gfsbk.openUploadStream(file.getFileName());uploadStream.write(file.getContent());ObjectId id = uploadStream.getFileId();uploadStream.flush();uploadStream.close();FileEntity filter = new FileEntity();filter.setId(id);filter = find(bucket,filter);return filter;}public FileEntity download(String bucket,FileEntity filter) throws IOException{filter = find(bucket,filter);if(filter==null){return null;}ByteArrayOutputStream out = new ByteArrayOutputStream();gfsbk = GridFSBuckets.create(db, bucket);gfsbk.downloadToStream(filter.getId(), out);filter.setContent(out.toByteArray());out.close();return filter;}public FileEntity find(String bucket,FileEntity filter){gfsbk = GridFSBuckets.create(db, bucket);System.out.println(filter.toBson());GridFSFile result = gfsbk.find(filter.toBson()).first();if(result==null){ return null;}filter.setId(result.getObjectId());filter.setSize(result.getLength());filter.setFileName(result.getFilename());filter.setUploadTime(result.getUploadDate());return filter;}}package com.huanle.utils.model;import java.util.Date;import javax.validation.constraints.Past;import org.bson.Document;
import org.bson.types.ObjectId;
import org.hibernate.validator.constraints.Range;import com.huanle.utils.annotation.FileContent;
import com.huanle.utils.annotation.FileName;
import com.huanle.utils.annotation.PlainString;/**文件辅助实体类* @author luchu**/
public class FileEntity {public static String ID="_id",FILE_NAME="fileName",SIZE="size",UPLOAD_TIME="uploadTime",CONTENT="content";private ObjectId id;@PlainString@FileNameprivate String fileName;@Range(max=41943040)private long size;@Pastprivate Date uploadTime;@FileContentprivate byte[] content;public Document toBson(){Document doc = new Document();if(this.id!=null){doc.append(ID, this.id);}if(this.fileName!=null){doc.append(FILE_NAME, this.fileName);}if(this.size!=0){doc.append(SIZE, this.size);}if(this.uploadTime!=null){doc.append(UPLOAD_TIME, this.uploadTime);}return doc;}}