Monday, February 23, 2009

How to use extra camel componets in servicemix-camel

When I was doing the spring clean up work for fuse ESB 3.x. I came across the issues of using the extra camel components within ESB3.x's servicemix-camel component.

Since Servicemix3's has same hierarchies of the class loaders with the J2EE application server, and the components the class loader is separated with the SU's. And Camel has lots of components, we just include the camel-core and camel-spring components in the servicemix-camel by default. When the user want to use other camel component, they always add the camel-xxx component into their SU lib.
In this way if there is a class which is loaded from the different SU classloader and registered into the camel-core's registry by servicemix-camel component , we will faced on the typical class cast exception in Servicemix3. Basically this exception is caused by the same class is loaded by different class loader.

Let me give you a real world issue.

In this case, when the SU redeployed, it will create a new deployer which will create a application context with the class loader of servicemix-camel component, and then using the SU's class loader to create a camel context.
Since the SU is redeployed, Servicemix will create a new class loader to load the SU's lib jars and resources.
When the SU initial the rmi component, boom , we meet the situation of same component loaded with different class loader, The class cast exception is thrown out.

Note, In Servicemix4 , we will not get that kind of issue , since the OSGI will help us to manage the relationship of the jars :).

The solution is putting the camel-xxx component and third part jars into servicemix-camel component's lib. You need to check out the servicemix-camel component's pom.xml and recompile the servicemix-camel component by adding the camel-xxx component dependency.

Let me take the latest servicemix-camel as an example

1. Checking out the servicemix-camel component's pom


svn co http://svn.apache.org/repos/asf/servicemix/components/engines/servicemix-camel/trunk/pom.xml


2. If you need camel-rmi component , you just put the dependency into the pom.xml


<dependency>
<groupid>org.apache.camel</groupid>
<artifactid>camel-rmi</artifactid>
<version>${camel-version}</version>
</dependency>


3. Running "mvn install" and copy the servicemix-camel-*.zip into the deploy directory

4. Write your servicemix-camel SU, make sure you don't include any camel relates jars into the SU's lib, you can use the <scope>provided</scope> to not packing the artifact.


<dependency>
<groupid>org.apache.camel</groupid>
<artifactid>camel-rmi</artifactid>
<version>${camel-version}</version>
<scope>provided</scope>
</dependency>

No comments:

Post a Comment

Post a Comment