The JMS specification defines ten levels of priority value, from zero (lowest priority) to 9 (highest priority). The specification suggests that clients consider 0–4 as gradations of normal priority, and priorities 5–9 as gradations of expedited priority.
Priority affects the order in which the server delivers messages to consumers (higher values first). The JMS specification does not require all providers to implement priority ordering of messages. (EMS supports priorities, but other JMS providers might not.)