ActiveMQ–Can’t have UDP Transport Connector Up and Running

Simply put, I can’t have ActiveMQ broker binds to a UDP port. What I saw from the output is this:

Starting UdpTransportServer@udp://0.0.0.0:61617@0

However, when I tried to list the UDP port, I found nothing:

$ netstat -an | grep 61617

Obviously, it’s about this class: ./activemq/transport/udp/UdpTransportServer.java.

    protected void doStart() throws Exception {
        LOG.info("Starting " + this);

        configuredTransport.setTransportListener(new TransportListener() {
            public void onCommand(Object o) {
                final Command command = (Command)o;
                processInboundConnection(command);
            }

            public void onException(IOException error) {
                LOG.error("Caught: " + error, error);
            }

            public void transportInterupted() {
            }

            public void transportResumed() {
            }
        });
        configuredTransport.start();
    }

According to UdpTransport.toString(), there is something really interesting:

    /**
     * @return pretty print of 'this'
     */
    public String toString() {
        if (description != null) {
            return description + port;
        } else {
            return getProtocolUriScheme() + targetAddress + "@" + port;
        }
    }

See?

Starting UdpTransportServer@udp://0.0.0.0:61617@0

This @0 thing. Zero is supposed to be the port!! How could it be?! I don’t know. Let’s figure it out later.