Tutorial-Example-ReportIncident-Part5

Part 5

We continue from part 4 where we have the routing in place. However as you might have noticed that we aren't quiet there yet with a nice solution.

These issues are still there as we:

• is creating and starting Camel manually
• is starting the routing by manually sending a message to direct:start

Of course for both issues there is a more convienient solution with Camel. But as this tutorial is very much about showing how things is done manually and also peeks how Camel does this internally for you. So let's get rocking

Starting Camel automatically

Our current deployment model is as a war and we have the web.xml to help start things. Well in fact we will leverage Spring to start the world . We use it's ContextListener

	<!-- the listener that kick-starts Spring -->
	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>

Then we need a standard Spring XML file so we create a new file in src/main/resources and name it camel-config.xml. Before we start editing this XML file we need to link to it from the web.xml file. So we add this snippet to the web.xml:

	<!-- location of spring xml files -->
	<context-param>
	    <param-name>contextConfigLocation</param-name>
            <param-value>classpath:camel-config.xml</param-value>
	</context-param>

Now we are ready to edit the camel-config.xml file that is a standard Spring XML bean file. So you can add standard spring beans and whatnot you like to do and can do with Spring.

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

</beans>

Now we are nearly there, we just need to add Camel to the Spring XML file, so Spring knows Camel exists and can start it. First we need to add Camel to the schema location in the top of the XML file.

       ...
       xsi:schemaLocation="
            http://activemq.apache.org/camel/schema/spring http://activemq.apache.org/camel/schema/spring/camel-spring.xsd
            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

Now we are ready to let Spring and Camel work together. What we need to do is adding a CamelContext to the Spring XML file. Camel ships with a CamelContextFactoryBean that is a Spring factory bean we should use for creating and initializing the SpringCamelContext. SpringCamelContext is extending CamelContext to be Spring aware so Camel and Spring can work nicely together. For instance the Registry will now use Spring bean lookup. So any spring bean can now easily be lookup and used from Camel. Well back to today's lesson. So we can create a SpringCamelContext using the factory bean as illustrated below:

   <bean id="camel" class="org.apache.camel.spring.CamelContextFactoryBean"/>

However this is not used very often as Spring has support for custom namespace, so Camel has a CamelNamespaceHandler so we can create Camel using nice XML syntax as:

    <camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
       ...
    </camelContext>

Adding route builder

Now we have Camel integrated but we still need to add our route bulder that we did manually from the javacode as:

    // append the routes to the context
    context.addRoutes(new ReportIncidentRoutes());

There are two solutions to this

• using spring bean
• package scanning

Using a spring bean we just declare the route builder using a regular spring bean:

   <bean id="myrouter" class="org.apache.camel.example.reportincident.ReportIncidentRoutes"/>

And then we can refer to it from our CamelContext:

    <camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
       <routeBuilderRef ref="myrouter"/>
    </camelContext>

So now when Spring start's it will read the camel-context.xml file and thus also start Camel as well. As SpringCamelContext is spring lifecycle event aware, Camel will also shutdown when Spring is shutting down. So when you stop the web application Spring will notify this and Camel is also shutdown nice and properly. So as an end user no need to worry.