Cannot iterate through MongoDB Collection

Question

As a step towards familiarising myself with MongoDB, I started to create simple Java Classes to perform CRUD in MongoDB. I was able to establish connection with MongoDB. Nevertheless, when I try to iterate through the MongoDB collection, I'm getting errors. Implemented Java class is shared here.

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import java.util.Iterator;
import org.bson.Document;
public class ReadMongo {
    public static void main( String args[] ) {
        //Creating a MongoDB client
        com.mongodb.client.MongoClient mongo = MongoClients.create("mongodb://localhost:27017");
        //Connecting to the database
        MongoDatabase database = mongo.getDatabase("myDB");
        //Creating a collection object
        MongoCollection<Document> collection = database.getCollection("myGrid");
        //Retrieving the documents
        FindIterable<Document> iterDoc = collection.find();
        Iterator it = iterDoc.iterator();
        while (it.hasNext()) {
            System.out.println(it.next());
        }
    }
}

Below I've shared the error log.

INFO: Cluster created with settings {hosts=[localhost:27017], mode=SINGLE, requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms', maxWaitQueueSize=500}
Exception in thread "main" java.lang.NoSuchMethodError: com.mongodb.internal.operation.SyncOperations.<init>(Lcom/mongodb/MongoNamespace;Ljava/lang/Class;Lcom/mongodb/ReadPreference;Lorg/bson/codecs/configuration/CodecRegistry;Lcom/mongodb/WriteConcern;Z)V
    at com.mongodb.client.internal.MongoCollectionImpl.<init>(MongoCollectionImpl.java:106)
    at com.mongodb.client.internal.MongoDatabaseImpl.getCollection(MongoDatabaseImpl.java:132)
    at com.mongodb.client.internal.MongoDatabaseImpl.getCollection(MongoDatabaseImpl.java:127)
    at ReadMongo.main(ReadMongo.java:14)

The line #14 corresponds to MongoCollection<Document> collection = database.getCollection("myGrid"); line.

In general, the code looks fine; see [Java Driver Examples](https://docs.mongodb.com/manual/tutorial/update-documents-with-aggregation-pipeline/). Do you have a MongoDB database software installed and the server is running? What is the version of MongoDB and Java Driver you are working with? — prasad_, Jun 30 '21 at 09:29

score 0 · Answer 1 · answered Jun 30 '21 at 13:05

I still don't know what's wrong with the above code. Nevertheless, I was able to solve this issue following these resources: (i) resource 1 and (ii) resource 2. The final working solutions is as follows.

import com.mongodb.MongoClient;
import com.mongodb.MongoClientURI;
import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCursor;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

public class MongoDB {
    
    public static MongoClient mongoClient;
    public static MongoDatabase database;
    
    public static void main(String[] args) {
        mongoClient = new MongoClient(new MongoClientURI("mongodb://localhost:27017"));
        database = mongoClient.getDatabase("myDB");
      
        FindIterable<Document> mydatabaserecords = database.getCollection("myGrid").find();
        MongoCursor<Document> iterator = mydatabaserecords.iterator();
        while (iterator.hasNext()) {
            Document doc = iterator.next();
            System.out.println(iterator.next());
        }
    }
}

Cannot iterate through MongoDB Collection

1 Answers1