RoutePolicy
Since Camel 2.1
A route policy org.apache.camel.spi.RoutePolicy
is used to control
route(s) at runtime. For example you can use it to determine whether a
route should be running or not. However the policies can support any
kind of use cases.
How it works
You associate a route with a given RoutePolicy
and then during
runtime Camel will invoke callbacks on this policy where you can
implement your custom logic. Camel provides a support class that is a
good base class to extend org.apache.camel.impl.RoutePolicySupport
.
There are these callbacks invoked:
-
onInit
Camel 2.3 -
onRemove
Camel 2.9 -
onStart
Camel 2.9 -
onStop
Camel 2.9 -
onSuspend
Camel 2.9 -
onResume
Camel 2.9 -
onExchangeBegin
-
onExchangeDone
See the Javadoc of the org.apache.camel.spi.RoutePolicy
for more
details. And also the implementation of the
org.apache.camel.impl.ThrottlingInflightRoutePolicy
for a concrete
example.
Camel provides the following policies out of the box:
-
org.apache.camel.impl.ThrottlingInflightRoutePolicy
- a throttling based policy that automatic suspends/resumes route(s) based on metrics from the current in flight exchanges. You can use this to dynamically throttle e.g. a JMS consumer, to avoid it consuming too fast.
As of Camel 2.5, Camel also provides an ability to schedule routes to be activated, deactivated, suspended and/or resumed at certain times during the day using a ScheduledRoutePolicy (offered via the camel-quartz component).
SuspendableService
If you want to dynamic suspend/resume routes as the
org.apache.camel.impl.ThrottlingRoutePolicy
does then its advised to
use org.apache.camel.SuspendableService
as it allows for fine
grained suspend
and resume
operations. And use the
org.apache.camel.util.ServiceHelper
to aid when invoking these
operations as it support fallback for regular
org.apache.camel.Service
instances.
ThrottlingInflightRoutePolicy
The ThrottlingInflightRoutePolicy
is triggered when an
Exchange is complete, which means that it requires
at least one Exchange to be complete before it
works.
The throttling inflight route policy has the following options:
Option | Default | Description |
---|---|---|
|
|
A scope for either |
|
|
The maximum threshold when the throttling will start to suspend the route if the current number of inflight exchanges is higher than this value. |
|
|
A percentage |
|
|
The logging level used for logging the throttling activity. |
|
|
The logger category. |
ThrottlingInflightRoutePolicy compared to the Throttler EIP
The ThrottlingInflightRoutePolicy
compared to
Throttler is that it does not block during
throttling. It does throttling that is approximate based, meaning that
its more coarse grained and not explicit precise as the
Throttler. The Throttler can
be much more accurate and only allow a specific number of messages being
passed per a given time unit. Also the ThrottlingInflightRoutePolicy
is based its metrics on number of inflight exchanges where as
Throttler is based on number of messages per time
unit.
ScheduledRoutePolicy
(Simple and Cron based) using camel Quartz
For more details check out the following links
Configuring Policy
You configure the route policy as follows from Java DSL, using the
routePolicy
method:
RoutePolicy myPolicy = new MyRoutePolicy();
from("seda:foo").routePolicy(myPolicy).to("mock:result");
In Spring XML its a bit different as follows using the
routePolicyRef
attribute:
<bean id="myPolicy" class="com.mycompany.MyRoutePolicy"/>
<route routePolicyRef="myPolicy">
<from uri="seda:foo"/>
<to uri="mock:result"/>
</route>
Configuring Policy Sets
RoutePolicy
has been further improved to allow addition of policy
sets or a collection of policies that are concurrently applied on a
route. The addition of policies is done as follows.
In the example below, the route testRoute
has a startPolicy
and throttlePolicy
applied concurrently. Both policies are applied
as necessary on the route.
<bean id="date" class="org.apache.camel.routepolicy.quartz.SimpleDate"/>
<bean id="startPolicy" class="org.apache.camel.routepolicy.quartz.SimpleScheduledRoutePolicy">
<property name="routeStartDate" ref="date"/>
<property name="routeStartRepeatCount" value="1"/>
<property name="routeStartRepeatInterval" value="3000"/>
</bean>
<bean id="throttlePolicy" class="org.apache.camel.impl.ThrottlingInflightRoutePolicy">
<property name="maxInflightExchanges" value="10"/>
</bean>
<camelContext id="testRouteContext" xmlns="http://camel.apache.org/schema/spring">
<route id="testRoute" autoStartup="false" routePolicyRef="startPolicy, throttlePolicy">
<from uri="seda:foo?concurrentConsumers=20"/>
<to uri="mock:result"/>
</route>
</camelContext>
Using RoutePolicyFactory
If you want to use a route policy for every route, you can use
a org.apache.camel.spi.RoutePolicyFactory
as a factory for creating
a RoutePolicy
instance for each route. This can be used when you
want to use the same kind of route policy for every routes. Then you
need to only configure the factory once, and every route created will
have the policy assigned.
There is API on CamelContext to add a factory, as shown below
context.addRoutePolicyFactory(new MyRoutePolicyFactory());
And from XML DSL you just define a <bean>
with the factory
<bean id="myRoutePolicyFactory" class="com.foo.MyRoutePolicyFactory"/>
The factory has a single method that creates the route policy
/**
* Creates a new {@link org.apache.camel.spi.RoutePolicy} which will be assigned to the given route.
*
* @param camelContext the camel context
* @param routeId the route id
* @param route the route definition
* @return the created {@link org.apache.camel.spi.RoutePolicy}, or <tt>null</tt> to not use a policy for this route
*/
RoutePolicy createRoutePolicy(CamelContext camelContext, String routeId, RouteDefinition route);
Note you can have as many route policy factories as you want. Just call
the addRoutePolicyFactory
again, or declare the other factories
as <bean>
in XML.