Camel Lifecycle
Camel uses a simple lifecycle interface called Service which has a single start() and stop() method.
Various classes implement Service such as CamelContext along with a number of Component and Endpoint classes.
When you use Camel you typically have to start the CamelContext which will start all the various components and endpoints and activate the routing rules until the context is stopped again.
If you are working with Spring you may wish to read the Camel Spring documentation.
CamelContext Lifecycle
The CamelContext
provides methods to control its lifecycle:
start
stop
suspend
Camel 2.5resume
Camel 2.5
The operations is paired: start/stop and suspend/resume.
Stop is performing a Graceful shutdown which means all its internal state, cache, etc is cleared. And the routes is being stopped in a graceful manner to ensure messages is given time to complete. If you start a CamelContext
after a stop, then its performing a cold start, recreating all the state, cache etc. again.
Instead you can use the suspend/resume operations. They will keep the CamelContext
warm and only suspend/stop routes using the same Graceful shutdown feature. This ensures messages is given time to complete.
End users is encouraged to use suspend/resume if you are temporary stopping a Camel application.
All these operations is available in JMX as well, so you can control Camel from a management console.
Service lifecycle
A service (org.apache.camel.Service
) in Camel adheres to the following lifecycle states as illustrated in the diagram below:
Notice: A service can optimally support suspend/resume by the org.apache.camel.SuspendableService
. This means not all services in Camel supports suspension. It's encouraged that consumers support suspension which allows to suspend/resume routes.
The org.apache.camel.impl.ServiceSupport
is a good base class to extend for custom services as it offers the basic functionally to keep track of state. You implement your custom logic in the doStart
, doStop
, doSuspend
, doResume
methods.
Routes lifecycle
Routes in Camel have the following operations to control its lifecycle
start
stop
suspend
resume
shutdown
The shutdown
operation will also remove the route, for example in JMX the route will then be unregistered and its gone. So only use shutdown if you really want to remove the route.
If a route consumer does not support suspension, it will fallback and stop the route instead.