Spring Integration - Inbound vs Outbound Channel Adapters

Question

What is the fundamental difference between inbound and outbound channel adapters?

Any examples would be very helpful.

I have reviewed the

Answer 1

Channel adapters are for one-way integration (gateways are bidirectional).

Concretely, inbound adapters are at the beginning of a flow, outbound adapters terminate a flow. Flows are typically rendered (and conceptually thought of as flowing from left to right)...

inbound-c-a->someComponent->someOtherComponent->outbound-ca

(where -> represents a channel).

There are two types of inbound channel adapters:

• MessageProducers
• MessageSources

MessageProducers are termed "message-driven" i.e. they unilaterally produce messages in a completely asynchronous manner, as soon as they are started; examples are JMS message-driven adapter, TCP inbound channel adapter, IMAP Idle (mail) channel adapter, etc.

MessageSources on the other hand are polled - a poller with some trigger causes the framework to ask the source for a message; the trigger can be on a fixed rate, cron expression etc. Examples are the (S)FTP adapters, Mail inbound adapter (POP3. IMAP).

Examples of outbound adapters are Mail outbound adapter (SMTP).

Gateways are two-way (request/reply).

Inbound gateways are where some external system sends a request and Spring Integration replies.

Outbound gateways are where Spring Integration makes the request and some external system replies.

I hope that clears things up.