Apollo 1.0 Extending Guide

Overview

Apollo support being extended in several ways. This guide documents all the supported extension points.

Adding your Extensions to the Apollo Class Path

Just create a .jar out of out code and add it to the ${apollo.home}/lib directory. When Apollo restarts it will add the new jar to it's class path.

Extending the JAXB model with new Objects

If you want to extend the Apollo xml configuration model to understand some custom JAXB object you have defined in your own packages, then you need to implement a Module class and then create a META-INF/services/org.apache.activemq.apollo/modules.index resource file in which you list it's class name.

Example module class:

package org.example
import org.apache.activemq.apollo.util.JaxbModule

class ExtensionJaxbModule extends JaxbModule {
  def xml_package = "org.example.dto"
}

Example META-INF/services/org.apache.activemq.apollo/jaxb-module.index resource:

org.example.ExtensionJaxbModule

Plugging into the Broker Lifecycle

You can implement custom [Service][] objects which get started / stopped when the broker starts and stops. Once you have packaged your custom service, and added it to the Apollo class path, you can update the apollo.xml to add the service so it gets started when apollo starts:

<service id='myservice' kind='org.example.MyService'/>

The id attribute is a unique service name of your service, and the kind attribute is the class name of your service.

If your service needs a reference to the Broker object which is running in, add the following field definition to your class:

var broker:Broker = null

The broker instance will be injected into your class instance before it gets started.

Your service can also get reference to to the configuration element used to define it if it defines the following field.

var config: CustomServiceDTO

This field will also get injected before getting started. The CustomServiceDTO.other field will contain any additional configuration elements defined within service element. For example, if you configured the service as follows:

<service id='myservice' kind='org.example.MyService'/>
  <options xmlns="http://example.org/myservice">
    <search>google.com</search>
  </options>
</service>

Then you could access the options DOM element using:

    val options = config.other.get(1).asInstanceOf[Element]

If you had defined JAXB object mappings for the <options> class then config will hold that object instead of generic DOM Element.