Async

Async

Available as of Camel 2.0

The asynchronous API in Camel have been rewritten for Camel 2.0, and the information on this page applies for Camel 2.0 and later.

A bit of background

The new Async API in Camel 2.0 leverages in much greater detail the Java Concurrency API and its support for executing tasks asynchronous.
Therefore the Camel Async API should be familiar for users with knowledge of the Java Concurrency API.

A few concepts to master

When doing messaging there are a few aspects to keep in mind.

First of all a caller can initiate a message exchange as either:

• request only
• request reply

Request only is when the caller sends a message but do not expect any reply. This is also sometimes known as fire and forget or event message.

The Request Reply is then caller sends a message and then waits for a reply. This is like the HTTP protocol that we use every day when we surf the web.
We send a request to fetch a web page and wait until the reply message comes with the web content.

In Camel a message is labeled with a Message Exchange Pattern that labels whether its a request only or request reply message. Camel uses the JBI term for this an uses

for the request only, and

for the request reply.

For both the request only and the request reply the routing in Camel can happen either synchronous or asynchronous. A sync is defined as the caller thread and the remaining routing and processing of the message is happening in the same thread and as sync the caller waits until this thread has done its work before the invocation can return to the caller and continue its work. This is illustrated in the diagram below:

TODO: picture