MongoDB offers a feature called tailable cursors, which allows applications to continuously retrieve new documents that are being added to a collection. This is particularly useful for scenarios where we want to react in real-time to changes in the database.

In this blog post, we will explore how to use tailable cursors in a Java application with MongoDB. Before diving into the code, make sure you have the MongoDB Java driver installed in your project.

Step 1: Creating a Tailable Cursor

To create a tailable cursor, we need to set the cursorType option to TailableAwait when querying the collection. Here’s an example:

MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("test");
MongoCollection<Document> collection = database.getCollection("myCollection");

FindIterable<Document> iterable = collection.find().cursorType(CursorType.TailableAwait);
MongoCursor<Document> cursor = iterable.iterator();

while (cursor.hasNext()) {
    Document document = cursor.next();
    System.out.println(document);
}

In the above code snippet, we first connect to the MongoDB server and retrieve a reference to the desired collection (myCollection). We then create a FindIterable by calling the find() method on the collection and set the cursorType option to TailableAwait. Finally, we obtain an iterator from the FindIterable and iterate over the cursor to retrieve the new documents as they arrive.

Step 2: Inserting new documents

To see the tailable cursor in action, we need to insert some documents into the collection. Here’s an example:

Document document1 = new Document("name", "John");
collection.insertOne(document1);

In the above code snippet, we create a new Document object representing the data we want to insert. We then call the insertOne() method on the collection and pass the Document as an argument to insert it into the database.

Step 3: Observing real-time changes

Now, if we run the above code snippet with the tailable cursor, it will continuously output new documents added to the collection in real-time.

Note: Tailable cursors are not supported on standalone MongoDB deployments. They require a replica set or a sharded cluster for their operation.

That’s it! Now you know how to use tailable cursors in a Java application with MongoDB. This feature can be extremely useful in scenarios where real-time data processing is required, such as log monitoring or real-time analytics.

For more information, you can refer to the official MongoDB documentation on Tailable Cursors.

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