本文介绍如何使用GridFS API把图片文件保存到MongoDB。GridFS API也能保存其他二进制文件，如视频和音乐文件。

1. 保存图片

下面代码使用photo命名空间，新的filename保存图片到MongoDB。

String newFileName = "mkyong-java-image";

File imageFile = new File("mongodb.png");

GridFS gfsPhoto = new GridFS(db, "photo");

GridFSInputFile gfsFile = gfsPhoto.createFile(imageFile);

gfsFile.setFilename(newFileName);

gfsFile.save();

2. 获取图片

String newFileName = "mkyong-java-image";

GridFS gfsPhoto = new GridFS(db, "photo");

GridFSDBFile imageForOutput = gfsPhoto.findOne(newFileName);

System.out.println(imageForOutput);

输出，图片以如下的JSON格式被保存：

{

"_id" :

{

"$oid" : "4dc9511a14a7d017fee35746"

} ,

"chunkSize" : 262144 ,

"length" : 22672 ,

"md5" : "1462a6cfa27669af1d8d21c2d7dd1f8b" ,

"filename" : "mkyong-java-image" ,

"contentType" : null ,

"uploadDate" :

{

"$date" : "2011-05-10T14:52:10Z"

} ,

"aliases" : null

}

3. 打印所有图片

使用DBCursor遍历所有图片。

GridFS gfsPhoto = new GridFS(db, "photo");

DBCursor cursor = gfsPhoto.getFileList();

while (cursor.hasNext()) {

System.out.println(cursor.next());

}

4. 保存为另一张图片

从MongoDB中获取图片并把它保存为另一张图片。

String newFileName = "mkyong-java-image";

GridFS gfsPhoto = new GridFS(db, "photo");

GridFSDBFile imageForOutput = gfsPhoto.findOne(newFileName);

imageForOutput.writeTo("mongodbNew.png"); //output to new file

5. 删除图片

String newFileName = "mkyong-java-image";

GridFS gfsPhoto = new GridFS(db, "photo");

gfsPhoto.remove(gfsPhoto.findOne(newFileName));

完整实例

import com.mongodb.DB;

import com.mongodb.DBCollection;

import com.mongodb.DBCursor;

import com.mongodb.MongoClient;

import com.mongodb.MongoException;

import com.mongodb.gridfs.GridFS;

import com.mongodb.gridfs.GridFSDBFile;

import com.mongodb.gridfs.GridFSInputFile;

import java.io.File;

import java.io.IOException;

import java.net.UnknownHostException;

public class SaveImage {

public static void main(String[] args) {

try {

MongoClient mongoClient = new MongoClient("localhost", 27017);

DB db = mongoClient.getDB("imagedb");

DBCollection collection = db.getCollection("dummyColl");

String newFileName = "mkyong-java-image";

File imageFile = new File("mongodb.png");

// create a "photo" namespace

GridFS gfsPhoto = new GridFS(db, "photo");

// get image file from local drive

GridFSInputFile gfsFile = gfsPhoto.createFile(imageFile);

// set a new filename for identify purpose

gfsFile.setFilename(newFileName);

// save the image file into mongoDB

gfsFile.save();

// print the result

DBCursor cursor = gfsPhoto.getFileList();

while (cursor.hasNext()) {

System.out.println(cursor.next());

}

// get image file by it's filename

GridFSDBFile imageForOutput = gfsPhoto.findOne(newFileName);

// save it into a new image file

imageForOutput.writeTo("mongodbNew.png");

// remove the image file from mongoDB

gfsPhoto.remove(gfsPhoto.findOne(newFileName));

System.out.println("Done");

} catch (UnknownHostException e) {

e.printStackTrace();

} catch (MongoException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

}