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In any database, we need to organize the data in a way that we can easily find that data when necessary. To do this, it is very important to create a unique identity.

In MongoDB, there is a built-in unique identification system using a field called ObjectId.

This article will discuss ObjectId and how we can generate it using Java program. To make the topic easier, we will see an example with explanation to make the topic easier.

ObjectId in MongoDB

ObjectId is the value that uniquely identifies a document in MongoDB through the field _id. When a user inserts a new document, the system automatically generates this field.

But sometimes, we have to create our own ObjectId according to our own preferences to provide a unique identifier for each document. If you are creating a Java program that can operate a MongoDB database, then you can check out the next section on generating ObjectId using Java.

Generate ObjectId using Java

In the following example, we will demonstrate how to create a Java program that can insert a document using a manually created ObjectId. To do this, you can check the following example.

import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import org.bson.types.ObjectId;
import com.mongodb.MongoClient;


public class MongoDBJava {

    public static void main(String[] args) {
        MongoClient mongoClient = new MongoClient( "localhost" , 27017 );

        // Selecting the database
        MongoDatabase mydb = mongoClient.getDatabase("Mydb");

        // Generating an ObjectId before creating the document
        ObjectId myid = new ObjectId();

        System.out.println("Generated ID: "+ myid.get());

        // Creating a new document object
        Document mydoc = new Document();

        // Appending data to the document
        mydoc.append("_id", myid);
        mydoc.append("Name", "Fred");
        mydoc.append("Email", "Fred@gmail.com");
        mydoc.append("Year", 2022);

        //Inserting the created document into the collection
        mydb.getCollection("mydata").insertOne(mydoc);
        System.out.println("Inserted document successfully");
    }
}

The purpose of each line is commented out. In the example, we first create a connection to the MongoDB database.

After that, we use the method getDatabase()select database and then generate a new ObjectId called myid.

We then created a Document object and append()appended the data to it using the method. Finally, we simply insertOne()inserted the document into our collection using the method.

After executing the above example, you will get the following output.

Generated ID: 6383c46f57dfc2483d89093c
Inserted document successfully

You will see the following document added to your MongoDB collection.

{ _id: ObjectId("6383c46f57dfc2483d89093c"),
  Name: 'Fred',
  Email: 'Fred@gmail.com',
  Year: 2022 }

Some important notes:

1. The program shared in this article is written in Java. So, make sure it is installed in your system.
2. First install and include the MongoDB jar file in your Java program. To download MongoDB jar, use this link.