Java Reference
In-Depth Information
Understanding Reliable Messaging
Problem
You think you might want to use reliable messaging (RM) in your applications.
Solution
Before jumping in, check out this introduction.
Messages get lost all the time. The sticky note falls off the fridge. The network has a slight
hiccup. As a result, messages can be delivered out of order, or not at all. HTTP is an “unre-
liable” protocol, meaning that it does not guarantee that data will be delivered completely, or
at all. HTTP is popular for many reasons, but when you're sending SOAP messages over it
in business transactions with dramatic financial implications, you need something to improve
the reliability of your client/service interactions.
WS-ReliableMessaging (WS-RM) attempts to make up for the fact that the networks on which
service technologies are based cannot guarantee that messages are properly delivered to their
destinations. WS-RM gives us the idea of delivery assurance, which can take one of four
forms:
AtMostOnce
Messages are delivered at most once, without duplication. Some messages can potentially
get lost.
AtLeastOnce
Messages are guaranteed to be delivered, but it's possible that some messages are de-
livered more than one time.
ExactlyOnce
No message will be duplicated.
InOrder
Messages will arrive at the service for processing in the order they were sent.
The last assurance,
InOrder
, can be combined with one of the other three to indicate your
WS-RM policy regarding how many times messages can be delivered and whether they must
be in order. If you don't care if they're in order, you can just leave that element out of the
policy.
