Spring integration channel message count - spring

Question

I have 2 questions. Here they are:
Is there any way to determine the number of messages waiting to be
processed in a spring integration channel while the number of
customers keep increasing along the time?
In the app context, I want to be able to define x instances of
bean y which x and y, both consumes from channel p, programmatically
increase or decrease the consumers based on the load.
There is an example showed in spring 2gx but it used rabbitmq to determine load.

Answer 1

For 1), Spring Integration channels are just beans like any other bean. Assuming that you're using a standard pollable channel, you can autowire it in by name and then get the number of messages waiting:
http://docs.spring.io/spring-integration/api/org/springframework/integration/channel/QueueChannel.html#getQueueSize()
You may also be able to introspect this through JMX if you want.
For 2)... To do that, you'll want to use an AOP proxy on top of an object pool, then wire the proxy into (what I assume is a) Service Activator. Those properties can be externalized with a PropertyPlaceholderConfigurer. So, as an example:
<bean id="propertyPlaceholder"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="systemPropertiesMode" value="2" />
<property name="locations" value="classpath:my_config_params.properties" />
</bean>
<bean id="myBusinessObjectImpl" class="com.mycompany.whatever.impl.MyServiceImpl"
scope="prototype" autowire-candidate="false" />
<bean id="myBusinessObjPool" class="org.springframework.aop.target.CommonsPoolTargetSource">
<property name="targetBeanName" value="myBusinessObjectImpl" />
<!-- THIS IS THE KEY. myconfig.params.poolsize is the name of the property in the my_config_params.properties above. -->
<property name="maxSize" value="${myconfig.params.poolsize}" />
</bean>
<bean id="myBusinessObject" class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="targetSource" ref="myBusinessObjPool" />
</bean>
<int:channel id="myInputChannel">
<int:queue size="500" />
</int:channel>
<int:service-activator inputChannel="myInputChannel" ref="myBusinessObject" method="processMessages">
<int:poller max-messages-per-poll="10" fixed-rate="5000"/>
</int:service>
This also allows you to make the Service Activator stateful.
Obligatory link to object pooling functionality:
http://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/aop-api.html#aop-ts-pool