JMS

Java Message Service: An interface implemented by most J2EE containers to provide point-to-point queueing and topic (publish/subscribe) behavior. JMS is frequently used by EJB's that need to start another process asynchronously.

What type messaging is provided by JMS?
Both synchronous and asynchronous.

How may messaging models do JMS provide for and what are they?
JMS provides for two messaging models, publish-and-subscribe and point-to-point queuing.

What is the main parts of JMS applications?
The main parts of JMS applications are:
--ConnectionFactory and Destination
--Connection
--Session
--MessageProducer
--MessageConsumer
--Message

What is the difference between durable and non-durable subscriptions?
Point-To-Point (PTP). This model allows exchanging messages via queues created for some purposes. A client can send and receive messages from one or several queues. PTP model is easier than pub/sub model.
A durable subscription gives a subscriber the freedom of receiving all messages from a topic, whereas a non-durable subscription doesn't make any guarantees about messages sent by others when a client was disconnected from a topic.