ActiveMQ 5.4: JMS Timer and CRON Scheduler

I've added a persistent scheduler engine to ActiveMQ, so that messages that are scheduled for delivery will always survive restarts. The scheduling of some message in the future can be useful - but deciding  a scheduling syntax that is flexible, but can also fit into Message header properties is a little tricky.  I've decided the best approach is to use a combination of different concepts - simple delay, repeats and CRON.

There are a few choices of around scheduling messages to deliver in the future(inspiration from java.util.Timer)  - a simple delay - this one will deliver the message in a minute:

long time = 60 * 1000;
message.setLongProperty(ScheduledMessage.AMQ_SCHEDULED_DELAY, time); 

producer.send(message); 

Delivery at a fixed rate - this example will delivery 10 messages, waiting 10 seconds between each message - note the repeat count is 9 (9 + first one = 10).
long delay = 30 * 1000;
long period = 10 * 1000;
int repeat = 10;
message.setLongProperty(ScheduledMessage.AMQ_SCHEDULED_DELAY, delay);
message.setLongProperty(ScheduledMessage.AMQ_SCHEDULED_PERIOD, period);
message.setIntProperty(ScheduledMessage.AMQ_SCHEDULED_REPEAT, COUNT repeat);
producer.send(message);


For more advanced messaging you can use CRON scheduling - this one will deliver a message at 2AM on the 12 day of every month:

message.setStringProperty(ScheduledMessage.AMQ_SCHEDULED_CRON, "0 2 12 * *");
producer.send(message);

You can combine delays and repeats with CRON. For example, you may wish to send 10 messages, every 30 minutes, with a delay of 10 seconds between each one.

message.setStringProperty(ScheduledMessage.AMQ_SCHEDULED_CRON, "30 * * * *");
message.setLongProperty(ScheduledMessage.AMQ_SCHEDULED_DELAY, 10*1000);
message.setLongProperty(ScheduledMessage.AMQ_SCHEDULED_PERIOD, 10*1000);
message.setIntProperty(ScheduledMessage.AMQ_SCHEDULED_REPEAT, 9);

As I quickly realised whilst testing -  having a persistent message scheduler that survives re-starts really needs management support - so that you can delete those pesky jobs that you accidentally scheduled ;). So there's JMX support - and the ActiveMQ Web Console has been updated too: