RoutePolicy

Available as of 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 dynamic 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, de-activated, 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:

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

Available as of Camel 2.7

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>
   </route>

See Also

• Route Throttling Example for an example using this in practice with the ThrottlingInflightRoutePolicy
• ScheduledRoutePolicy for information on policy based scheduling capability for camel routes
• Architecture