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How to query documents using "_id" field in Java mongodb driver?
I am trying to find documents in MongoDB by searching on "_id" key. My document looks like this-
{
  "_id" : ObjectId("4f693d40e4b04cde19f17205"),
  "hostname" : "hostnameGoesHere",
  "OSType" : "OSTypeGoesHere"
}

I am trying to search this document as- 
ObjectId id= new ObjectId("4f693d40e4b04cde19f17205");        
BasicDBObject obj = new BasicDBObject();        
obj.append("_id", id);        
BasicDBObject query = new BasicDBObject();        
query.putAll(query);

But I get below error- 
error: reference to putAll is ambiguous, both method putAll(Map) in BasicBSONObject and method putAll(BSONObject) in BasicBSONObject match
        query.putAll(query);

The append method of BasicDBObject supports (String Key, Value) and if I pass "_id" as String to this method, no documents are matched. 
So my question is how do I pass "_id"? 

Solved it by using query as- 
query.putAll((BSONObject)query);


Not sure if others might be searching for answers on this topic, but here is the easiest way to search for a MongoDB record based on "_id". The MongoDB documentation is not updated and still shows ObjectId as being part of the com.mongodb package (it also generally does not give a lot of information on searching by ObjectId).
import org.bson.types.ObjectId;

public DBObject findDocumentById(String id) {

    BasicDBObject query = new BasicDBObject();
    query.put("_id", new ObjectId(id));

    DBObject dbObj = collection.findOne(query);
    return dbObj;
}


Is it outdated?

For those who are seeking a more up to date method, especially with 3.4:
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import org.bson.types.ObjectId;

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

//......
MongoCollection<Document> myCollection = database.getCollection("myCollection");
Document document = myCollection.find(eq("_id", new ObjectId("4f693d40e4b04cde19f17205"))).first();
if (document == null) {
    //Document does not exist
} else {
    //We found the document
}


can we use findOne here?

I don't think that we can use that method anymore. That was part of the old API http://api.mongodb.com/java/2.14/com/mongodb/DBCollection.html
The new is a slightly different one http://api.mongodb.com/java/3.0/com/mongodb/async/client/MongoCollection.html

the eq is not applicable to 3.12?

You can do this
 ObjectId id= new ObjectId("4f693d40e4b04cde19f17205");        
    BasicDBObject obj = new BasicDBObject();        
    obj.append("_id", id);        
    BasicDBObject query = new BasicDBObject();        
    query.putAll((BSONObject)query);


The more simple way to do this is:
Bson filter = Filters.eq("_id", new ObjectId("4f693d40e4b04cde19f17205"));
mongoConfig.getMongoTemplate().getCollection("myCollection").find(filter);


Reference here:
https://www.baeldung.com/mongodb-query-documents-id

I found a way around, with a little bit more of code, requires a string representing the id to be found passed as argument.
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.model.Filters;
import org.bson.conversions.Bson;
import org.bson.Document;
import org.bson.types.ObjectId;   

[...]

public static void findCustomerById(String id) {
    try (MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017")) {
        MongoDatabase database = mongoClient.getDatabase("database_name");
        Bson filter = Filters.eq("_id", new ObjectId(id));
        MongoCollection<Document> collection = database.getCollection("customer");

        //Tries to find the document
        Document doc = collection. Find(filter).first();
        //prints the document
        System.out.println(doc.toJson());
    } catch (Exception e) {
        System.out.println("Error finding document");
        System.out.println("Error in: " + e.getMessage());
        e.printStackTrace();
    }


Don't forget to add the collectionName parameter if your class and collectionName don't match.  I landed on this question because my _id query wasn't working even though it looked good at first blush.

You can try this snippet:
ObjectId id= new ObjectId("4f693d40e4b04cde19f17205");        
BasicDBObject obj = new BasicDBObject();        
obj.append("_id", id);        
BasicDBObject query = new BasicDBObject();        
query.putAll((BSONObject)obj);


How is this different from Nifras Nipy's answer?
