面试题与答案

JMS specification defines a transaction mechanisms allowing clients to send and receive groups of logically bounded messages as a single unit of information. A Session may be marked as transacted. It means that all messages sent in a session are considered as parts of a transaction. A set of messages can be committed (commit() method) or rolled back (rollback() method). If a provider supports distributed transactions, it's recommended to use XAResource API.

Point-to-point (P2P)
In point-to-point, messages are sent via queues. Messages are put onto the queues by the message producers (the clients). The message consumer is responsible for pulling the message from the queue. Point-to-point is typically used when a given message must be processed (received) only once by a given consumer. In this way, there is only one consumer of the given message.
Publish-and-subscribe (pub/sub)
In publish-and-subscribe, messages are sent through topics. Messages are published to topics by the message producers. The messages may be received by any consumers that subscribe to the given topic. In this way, a message may be received, or processed, by multiple consumers.

1. App server creates the server session and stores them in a pool.
2. Connection consumer uses the server session to put messages in the session of the JMS.
3. Server session is the one that spawns the JMS session.
4. Applications written by Application programmers creates the message listener.