For the most recent version of the reference documentation, see our MongoDB Java Driver documentation site.
- MongoDB Driver
- Tutorials
- GridFS
GridFS
GridFS is a specification for storing and retrieving files that exceed the BSON document size limit of 16MB. Instead of storing a file in a single document, GridFS divides a file into parts, or chunks, and stores each of those chunks as a separate document.
When you query a GridFS store for a file, the Java driver will reassemble the chunks as needed.
The following code snippets come from the GridFSTour.java
example code
that can be found with the driver source on github.
Prerequisites
Include the following import statements:
import com.mongodb.Block;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.gridfs.*;
import com.mongodb.client.gridfs.model.*;
import org.bson.Document;
import org.bson.types.ObjectId;
import java.io.*;
import java.nio.file.Files;
import java.nio.charset.StandardCharsets;
import static com.mongodb.client.model.Filters.eq;
Connect to a MongoDB Deployment
Connect to a MongoDB deployment and declare and define a MongoDatabase
instance.
For example, include the following code to connect to a standalone MongoDB deployment running on localhost on port 27017
:
MongoClient mongoClient = MongoClients.create();
For additional information on connecting to MongoDB, see Connect to MongoDB.
Create a GridFS Bucket
GridFS stores files in two collections: a chunks
collection stores the file chunks, and a files
collection stores file metadata. The two collections are in a common bucket and the collection names are prefixed with the bucket name.
The Java driver provides the GridFSBuckets.create()
method
to create the GridFSBucket
.
MongoDatabase myDatabase = mongoClient.getDatabase("mydb");
// Create a gridFSBucket using the default bucket name "fs"
GridFSBucket gridFSBucket = GridFSBuckets.create(myDatabase);
You can specify a bucket name to GridFSBuckets.create()
method.
// Create a gridFSBucket with a custom bucket name "files"
GridFSBucket gridFSFilesBucket = GridFSBuckets.create(myDatabase, "files");
Note
GridFS will automatically create indexes on the files
and chunks
collections on first upload of data into the GridFS bucket.
Upload to GridFS
To upload data into GridFS, you can upload from an InputStream
or write data to a GridFSUploadStream
.
UploadFromStream
The GridFSBucket.uploadFromStream
method reads the contents of an InputStream
and saves it to the GridFSBucket
.
You can use the GridFSUploadOptions
to configure the chunk size or include additional metadata.
The following example uploads an InputStream
into GridFSBucket
:
// Get the input stream
try {
InputStream streamToUploadFrom = new FileInputStream(new File("/tmp/mongodb-tutorial.pdf"));
// Create some custom options
GridFSUploadOptions options = new GridFSUploadOptions()
.chunkSizeBytes(358400)
.metadata(new Document("type", "presentation"));
ObjectId fileId = gridFSBucket.uploadFromStream("mongodb-tutorial", streamToUploadFrom, options);
} catch (FileNotFoundException e){
// handle exception
}
OpenUploadStream
You can write data to a GridFSUploadStream
which extends OutputStream
. The GridFSBucket.openUploadStream
method returns a GridFSUploadStream
.
The GridFSUploadStream
buffers data until it reaches the chunkSizeBytes
and then inserts the chunk into the chunks
collection. When the GridFSUploadStream
is closed, the final chunk is written and the file metadata is inserted into the files
collection.
The following example uploads into a GridFSBucket
via the returned GridFSUploadStream
:
try {
GridFSUploadOptions options = new GridFSUploadOptions()
.chunkSizeBytes(358400)
.metadata(new Document("type", "presentation"));
GridFSUploadStream uploadStream = gridFSFilesBucket.openUploadStream("mongodb-tutorial-2", options);
byte[] data = Files.readAllBytes(new File("/tmp/MongoDB-manual-master.pdf").toPath());
uploadStream.write(data);
uploadStream.close();
System.out.println("The fileId of the uploaded file is: " + uploadStream.getObjectId().toHexString());
} catch(IOException e){
// handle exception
}
Find Files Stored in GridFS
To find the files stored in the GridFSBucket
use the find
method.
The following example prints out the filename of each file stored:
gridFSBucket.find().forEach(
new Block<GridFSFile>() {
public void apply(final GridFSFile gridFSFile) {
System.out.println(gridFSFile.getFilename());
}
});
You can also provide a custom filter to limit the results returned. The following example prints out the filenames of all files with a “image/png” value set as the contentType in the user defined metadata document:
gridFSBucket.find(eq("metadata.contentType", "image/png")).forEach(
new Block<GridFSFile>() {
public void apply(final GridFSFile gridFSFile) {
System.out.println(gridFSFile.getFilename());
}
});
Download from GridFS
There are various ways to download data from GridFS.
DownloadToStream
The downloadToStream
method reads the contents from MongoDB and writes the data directly to the provided OutputStream
.
To download a file by its file _id
, pass the _id
to the method. The
following example downloads a file by its file _id
into the provided
OutputStream
:
ObjectId fileId; //The id of a file uploaded to GridFS, initialize to valid file id
try {
FileOutputStream streamToDownloadTo = new FileOutputStream("/tmp/mongodb-tutorial.pdf");
gridFSBucket.downloadToStream(fileId, streamToDownloadTo);
streamToDownloadTo.close();
System.out.println(streamToDownloadTo.toString());
} catch (IOException e) {
// handle exception
}
If you don’t know the _id
of the file but know the filename, then you can pass the filename to the downloadToStream
method. By default, it will download the latest version of the file. Use the GridFSDownloadOptions
to configure which version to download.
The following example downloads the original version of the file named “mongodb-tutorial” into the OutputStream
:
try {
FileOutputStream streamToDownloadTo = new FileOutputStream("/tmp/mongodb-tutorial.pdf");
GridFSDownloadOptions downloadOptions = new GridFSDownloadOptions().revision(0);
gridFSBucket.downloadToStream("mongodb-tutorial", streamToDownloadTo, downloadOptions);
streamToDownloadTo.close();
} catch (IOException e) {
// handle exception
}
OpenDownloadStream
The openDownloadStream
method returns a GridFSDownloadStream
which extends InputStream
.
The following example reads from the GridFSBucket
via the returned InputStream
:
ObjectId fileId; //The id of a file uploaded to GridFS, initialize to valid file id
GridFSDownloadStream downloadStream = gridFSBucket.openDownloadStream(fileId);
int fileLength = (int) downloadStream.getGridFSFile().getLength();
byte[] bytesToWriteTo = new byte[fileLength];
downloadStream.read(bytesToWriteTo);
downloadStream.close();
System.out.println(new String(bytesToWriteTo, StandardCharsets.UTF_8));
You can also pass the filename to the openDownloadStream
method. By default it will download the latest version of the file. Use the GridFSDownloadOptions
to configure which version to download.
The following example downloads the latest version of the file named “sampleData” into the OutputStream
:
GridFSDownloadStream downloadStream = gridFSBucket.openDownloadStream("sampleData");
int fileLength = (int) downloadStream.getGridFSFile().getLength();
byte[] bytesToWriteTo = new byte[fileLength];
downloadStream.read(bytesToWriteTo);
downloadStream.close();
System.out.println(new String(bytesToWriteTo, StandardCharsets.UTF_8));
Rename files
If you should need to rename a file, then use the rename
method.
The following example renames a file to “mongodbTutorial”:
ObjectId fileId; //ObjectId of a file uploaded to GridFS
gridFSBucket.rename(fileId, "mongodbTutorial");
Note
The rename
method requires an ObjectId
rather than a filename
to ensure the correct file is renamed.
To rename multiple revisions of the same filename, first retrieve the full list of files. Then for every file that should be renamed then execute rename
with the corresponding _id
.
Delete files
To delete a file from the GridFSBucket
use the delete
method.
The following example deletes a file from the GridFSBucket
:
ObjectId fileId; //ObjectId of a file uploaded to GridFS
gridFSBucket.delete(fileId);