find in MongoCollection

I have a MongoCollection<Document> in which I assign a collection. I’m trying to find a user by his id.

user = (Document) usersCollection.find(new Document("_id", username));

with that I’m getting an error

java.lang.ClassCastException: com.mongodb.FindIterableImpl cannot be cast to org.bson.Document

When I try

    BasicDBObject query = new BasicDBObject(); 
    BasicDBObject fields = new BasicDBObject("_id", username);
    usersCollection.find(query, fields);

I’m getting an error

The method find(Bson, Class) in the type MongoCollection is not applicable for the arguments (BasicDBObject, BasicDBObject)

Answer

Try to create a filter to pass to the find() method to get a subset of the documents in your collection. For example, to find the document for which the value of the _id field is test, you would do the following:

import static com.mongodb.client.model.Filters.*;

MongoClient client = new MongoClient();
MongoDatabase database = client.getDatabase("mydb");
MongoCollection<Document> collection = database.getCollection("mycoll");
Document myDoc = collection.find(eq("_id", "test")).first();
System.out.println(myDoc.toJson());