Saturday, July 5, 2014

Study MongoDB GridFS with java example

In the past, we have learned basic MongoDB and study data model, in this article , we will study MongoDB GridFS by storing a file into MongoDB. Below is the java simple application to show how to store, retrieve, and delete eventually.

import com.mongodb.DB;
import com.mongodb.DBCursor;
import com.mongodb.Mongo;
import com.mongodb.MongoException;
import com.mongodb.gridfs.GridFS;
import com.mongodb.gridfs.GridFSDBFile;
import com.mongodb.gridfs.GridFSInputFile;

public class LearnMongo {

public static void main(String[] args) throws MongoException, IOException {
Mongo mongo = new Mongo("", 27017);
DB db = mongo.getDB("mp3db");

// save image
String newFilename = "django.mp3";
File mp3File = new File("src/resources/django.mp3");
GridFS gfsMp3 = new GridFS(db, "mp3");
GridFSInputFile gfsFile = gfsMp3.createFile(mp3File);

// get mp3
GridFSDBFile imageForOutput = gfsMp3.findOne(newFilename);

// print image
DBCursor cursor = gfsMp3.getFileList();
while (cursor.hasNext()) {

// save into another image

// delete image



We start by connecting to the server, so with this example MongoDB instance running on server on port 27017. You may want to check the configuration for MongoDB if you connect remotely as the default MongoDB configuration only listen to localhost.

Then we form a MongoDB DB object on mp3db. You can store other object as well but for this example, I'm going to store a mp3. With this ready, we are going to store the mp3. The important piece of code is probably below.
GridFS gfsMp3 = new GridFS(db, "mp3");
GridFSInputFile gfsFile = gfsMp3.createFile(mp3File);

Instantiate two object, GrisFS and GridFSInputFile. You can set additional information like filename, content type. Calling will save the object into MongoDB. If you have access to MongoDB cli, command such as > db.mp3.files.find(); will shown below the output.
{ "_id" : ObjectId("53ad60f944aeaca83109d253"), "chunkSize" : NumberLong(262144), "length" : NumberLong(316773), "md5" : "7293e9fd795e2bb6d5035e5b69cb2923", "filename" : "django.mp3", "contentType" : "audio/mpeg", "uploadDate" : ISODate("2014-06-27T12:18:01.934Z"), "aliases" : null }

To find the mp3, you can use the code, GridFSDBFile imageForOutput = gfsMp3.findOne(newFilename); below is the output.
{ "_id" : { "$oid" : "53ad60f944aeaca83109d253"} , "chunkSize" : 262144 , "length" : 316773 , "md5" : "7293e9fd795e2bb6d5035e5b69cb2923" , "filename" : "django.mp3" , "contentType" : "audio/mpeg" , "uploadDate" : { "$date" : "2014-06-27T12:18:01Z"} , "aliases" : null }

You can also use GridFS.getFileList(); to retrieve all the files currently store on this database. The code continue on writing the object into a file. As you can see, I'm writing to desktop just to ensure it is not from the source.

I end this article by removing the object in the MongoDB database.

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