RabbitMQ : Can I get latest n messages?

Question

I'm new on RabbitMQ.

I implemented websocket server with tyrus to get messages on real-time like Push Server with the book RabbitMQ essentials.

however, When I disconnected and reconnect, the server send all messages because I implemented like this.

consumer = new DefaultConsumer(channel)
{
    @Override
    public void handleDelivery(final String consumerTag,
                   final Envelope envelope,
                   final BasicProperties properties,
                   final byte[] body) throws IOException
    {
    handler.handleDelivery(channel, envelope, properties, body);
    }

};

So, I want to get 20 latest messages when users have requested(like scrolling), however, in honestly, I can't imagine how to implement it.

I want to implement these things.

1. When a user connected to websocket server, then server sends latest 20 messages.

2. When a user opened inbox layout and reached scroll bottom, then server sends next 20 messages.

3. A new message for this user while has connected, then server send on real-time.

Answer 1

You need to use prefetch count to limit consuming of unacknowledged messages at your consumer startup.

You can use basicQos method on your channel. From RabbitMQ docs:

Channel channel = ...;
Consumer consumer = ...;
channel.basicQos(20); // Per consumer limit
channel.basicConsume("my-queue", false, consumer);

Refer RabbitMQ docs for more detail: http://www.rabbitmq.com/consumer-prefetch.html