When saving a new file, GridFSInputFile overrides getMetadata() to return _metadata instead of _metadata.get("metadata"). As a result, metadata values are saved directly in the files object, not in a field named "metadata" as indicated in the spec. For example, we end up with:

{ "_id" : ObjectId(...), "chunkSize" : ..., "length" : ..., "myMetadataField" : "myValue" }

instead of:

{ "_id" : ObjectId(...), "chunkSize" : ..., "length" : ..., metadata :

{ "myMetadataField" : "myValue" }

}

I would think GridFSInputFile should not override getMetadata() at all, but instead GridFSFile should either provide a setMetadata(DBObject) method or getMetadata() should create an object to return and simply not save it to the database if it's empty. I can currently work around this bug by creating a new BasicDBObject and calling myGridFSInputFile.put("metadata", myBasicDBObject), but in my opinion I shouldn't need to know about the specific implementation of DBObject in use, or the fact that metadata is stored as a field named "metadata".