inserting image into mongo from java result in a strange error - mongodb-query

Question

I have the following code for saving image in mongodb:
public static void insertImage() throws Exception {
String newFileName = "mkyong-java-image";
File imageFile = new File("c:\\JavaWebHosting.png");
GridFS gfsPhoto = new GridFS(db, "photo");
GridFSInputFile gfsFile = gfsPhoto.createFile(imageFile);
gfsFile.setFilename(newFileName);
gfsFile.save();
}
And I got this from this link:
link for code
But when I use that I get the following error and I do not know how to fix it ... Can anyone help?
Exception in thread "main" java.lang.NullPointerException
at com.mongodb.gridfs.GridFS.<init>(GridFS.java:97)
for more explanation the error is at exactly this line:
GridFS gfsPhoto = new GridFS(db, "photo");
Update:
Here is the code for creating db connection
public static DB getDBConnection() {
// If it's not connected to the database, make connection
if (db == null) {
initialize();
makeConnections();
}
return db;
}
private static void makeConnections() {
MongoCredential credential = MongoCredential.createMongoCRCredential(dbUser, dbName, dbPass.toCharArray());
MongoClient mongoClient;
try {
mongoClient = new MongoClient(new ServerAddress(dbHost, Integer.parseInt(dbPort)), Arrays.asList(credential));
db = mongoClient.getDB(dbName);
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
Update:
String newFileName = "mkyong-java-image";
File imageFile = new File("D:/1.jpg");
db = MongoDB.getDBConnection();
collection = db.getCollection("test");
// 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("D:\\JavaWebHostingNew.jpg");
// remove the image file from mongoDB
// gfsPhoto.remove(gfsPhoto.findOne(newFileName));
System.out.println("Done");