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Combining iPOJO and Configuration Admin

This page presents how creating, reconfiguring and destroying iPOJO component instance with the OSGi Configuration Admin.

Configuration Admin

The Configuration Admin service is a configuration manager describe in the OSGi R4 Compendium. It allows an operator to set the configuration information of deployed applications The Configuration Admin defines the Configuration as the process of defining the configuration data of applications and assuring that those applications receive that data when they are running. The Configuration Admin is becoming an important piece on OSGi Gateway. It is become the standard way to configure applications on OSGi gateways.

Why using Configuration Admin with iPOJO

As the configuration admin offer an administration support, it seems reasonable to combine iPOJO and the Configuration Admin to control the gateway. Indeed, thanks to the configuration admin it should be possible to:

  • Create new component instances
  • Configuring / reconfiguring these instances
  • Destroying these instances
  • Reconfiguring instances by using Managed Services (not addressed in this page, see here for further information)

The configuration admin is persistent, so stored configuration will be reload it the framework restarts.
Moreover, using the configuration admin allows avoiding describing instances inside iPOJO metadata file. These instances are created by inserting new configurations in the configuration admin.

Combining iPOJO and the Configuration Admin

iPOJO has a component type concept. For each (public) component type, a ManagedServiceFactory is published. For each configurations matching with the component type from the Configuration Admin, a new component instance is created. Moreover, when this configuration is updated, the instance is dynamically reconfigured. If the configuration is removed, the instance is disposed.

If a new Configuration is created:

  • If the factory is available or an instance is create immediately,
  • Else the factory is not available and the instance will be created as soon as the factory appears.

Examples

This section presents 3 examples about the management of iPOJO instances with the configuration admin:

  • A simple instantiation example and destruction
  • An instantiation with property injection and dynamic reconfiguration
  • A property propagation example

All these examples are downloadable here. The archive contains both the project sources and a pre-configured version of felix.
To compile the project, launch ant from the config.admin.tutorial directory
Then, you can launch Felix by launching the following command from the felix directory:

Java -jar bin/felix.jar

Prerequisites

Let's take 4 Felix shell commands to manage configuration admin configurations (available in the example archive):

  • create_conf <type> <property-key=property-value>* allows to create a new Factory Configuration attached to the given type. The configuration contains the given properties.
  • update_conf <configuration_name> < property-key=property-value>* allows to update the configuration with the given name with the given properties.
  • delete_conf <configuration_name> allows deleting the configuration with the given name. If the name is 'all', delete all stored configurations.
  • list_conf allows listing all stored configuration.

Moreover iPOJO and an implementation of the Configuration Admin must be deployed on the gateway:

-> ps
START LEVEL 1
   ID   State         Level  Name
[   0] [Active     ] [    0] System Bundle (1.0.3)
[   1] [Active     ] [    1] Apache Felix Shell Service (1.0.0)
[   2] [Active     ] [    1] Apache Felix Shell TUI (1.0.0)
[   3] [Active     ] [    1] Apache Felix Bundle Repository (1.0.2)
[   4] [Active     ] [    1] Apache Felix Configuration Admin Service (1.0.10) 
[   5] [Active     ] [    1] Apache Felix iPOJO (1.2.0) 
[   6] [Active     ] [    1] Apache Felix iPOJO Arch Command (1.2.0)

Simple Instantiation

Imagine the following very simple component implementation:

public class Hello1 {
    public Hello1() {
        System.out.println("Hello");
    }
}

The component type is defined with following metadata:

<component 
    classname="org.apache.felix.ipojo.example.ca.component.Hello1" 
    factory="hello1" immediate="true" architecture="true"/>

The defined component type (Hello1) just creates a Hello1 object when the instance is created (thanks to the immediate attribute).
So if we deploy this bundle and add a consistent configuration we obtain (note that bundle need to be already compiled):

-> start file:..\config.admin.tutorial\output\config.admin.tutorial.jar
-> create_conf org.apache.felix.ipojo.example.ca.component.Hello1 
Insert the configuration : {org.apache.felix.ipojo.example.ca.component.Hello1}
-> Hello

Note: Debug messages from the configuration admin were removed
So as predicted, the Hello message appears. To be really sure of the creating, we can ask for the instance architecture (the component type allows architecture introspection thank to the architecture attribute):

-> arch 
Instance ArchCommand -> valid 
Instance org.apache.felix.ipojo.example.ca.component.Hello1.e40fe80a-2c0d-4c51-b00b-a82565874cd8 -> valid 
-> 
-> arch -instance 
org.apache.felix.ipojo.example.ca.component.Hello1.e40fe80a-2c0d-4c51-b00b-a82565874cd8 
instance name=
    "org.apache.felix.ipojo.example.ca.component.Hello1.e40fe80a-2c0d-4c51-b00b-a82565874cd8" 
        component.type="hello1" 
        state="valid" bundle="7" 
    object name="org.apache.felix.ipojo.example.ca.component.Hello1@120cc56" 
    handler 
        name="org.apache.felix.ipojo.handlers.lifecycle.callback.LifecycleCallbackHandler" 
        state="valid" 
    handler 
        name="org.apache.felix.ipojo.handlers.architecture.ArchitectureHandler" 
        state="valid" 
->

So, the instance is correctly created. The name of the instance was created by the configuration admin. It could change according to your configuration admin implementation.
Then, we can delete the instance by removing the configuration from the configuration admin:

-> delete_conf 
org.apache.felix.ipojo.example.ca.component.Hello1.e40fe80a-2c0d-4c51-b00b-a82565874cd8 
Delete the configuration : 
org.apache.felix.ipojo.example.ca.component.Hello1.e40fe80a-2c0d-4c51-b00b-a82565874cd8 
-> arch 
Instance ArchCommand -> valid

So, arch does no more displayed any hello instances, the created instance was disposed.

Reconfiguring instances with the Configuration Admin

Imagine the following component implementation:

public class Hello2 {
     String m_name;
    public void stop() {
        System.out.println("Good by " + m_name);
    }
    public void setName(String newName) {
        m_name = newName;
        System.out.println("Hello " + m_name);
    }

And the following metadata:

<component 
        classname="org.apache.felix.ipojo.example.ca.component.Hello2" 
        factory="hello2" immediate="true" architecture="true">
	<callback transition="validate" method="stop"/>
	<properties>
		<property field="m_name" name="to" method="setName"/>
	</properties>
</component>

The defined component type (Hello2) write "Hello + $name" when the property 'to' (attached to the field m_name) receive a new value. A value is necessary insert in the instance configuration. Moreover when killed, the instance will display a "Good By" message.
Let's play a simple scenario:

  • Create a Hello2 instance
  • Update the instance configuration
  • Kill the created instance
-> create_conf org.apache.felix.ipojo.example.ca.component.Hello2 to=ipojo 
Insert the configuration : 
{service.factoryPid=org.apache.felix.ipojo.example.ca.component.Hello2, to=ipojo} 
Created configuration: 
org.apache.felix.ipojo.example.ca.component.Hello2.75082279-9b4b-4c49-b0e0-8efb38b67aa3 
Hello ipojo 
-> list_conf 
org.apache.felix.ipojo.example.ca.component.Hello2.75082279-9b4b-4c49-b0e0-8efb38b67aa3 : 
 {service.pid=org.apache.felix.ipojo.example.ca.component.Hello2.75082279-9b4b-4c49-b0e0-8efb38b67aa3, 
  service.factorypid=org.apache.felix.ipojo.example.ca.component.Hello2, 
to=ipojo} 
-> update_conf 
org.apache.felix.ipojo.example.ca.component.Hello2.75082279-9b4b-4c49-b0e0-8efb38b67aa3 to=felix 
Update: 
pid=org.apache.felix.ipojo.example.ca.component.Hello2.75082279-9b4b-4c49-b0e0-8efb38b67aa3 
Update the configuration : {to=felix} 
Hello felix 
-> delete_conf 
org.apache.felix.ipojo.example.ca.component.Hello2.75082279-9b4b-4c49-b0e0-8efb38b67aa3 
Delete the configuration : 
org.apache.felix.ipojo.example.ca.component.Hello2.75082279-9b4b-4c49-b0e0-8efb38b67aa3 
Good by felix-> list_conf

In this simple scenario, we see that when the configuration is updated, the instance receives the new value. The setName method is immediately invoked to inject the new value. Moreover, when the configuration is deleted, the instance is going to be killed: the "Good Bye" message appears and the instance is disposed.
Obviously it is possible to create several instance of the same type:

-> create_conf org.apache.felix.ipojo.example.ca.component.Hello2 to=ipojo 
Insert the configuration : 
{service.factoryPid=org.apache.felix.ipojo.example.ca.component.Hello2, to=ipojo} 
Hello ipojo 
-> create_conf org.apache.felix.ipojo.example.ca.component.Hello2 to=felix 
Insert the configuration : 
{service.factoryPid=org.apache.felix.ipojo.example.ca.component.Hello2, to=felix} 
Hello felix 
-> arch 
Instance ArchCommand -> valid 
Instance org.apache.felix.ipojo.example.ca.component.Hello2.aaf1927c-1a81-490d-bd7b-21b13d454987 -> valid 
Instance org.apache.felix.ipojo.example.ca.component.Hello2.9344fdbe-c35e-4afc-b839-f7ad0ea59a9d -> valid

The 'arch' command displays the two created instances.

Delete configurations

you can delete all created configurations with the delete_conf all command

Property Propagation

It is possible to propagate the instance configuration to the published service properties. To activate property propagation you need to write the 'propagation' attribute in the 'properties' element as in

<component 
    classname="org.apache.felix.ipojo.example.ca.component.Hello3"
    factory="hello3" architecture="true">
	<provides/>
	<properties propagation="true">
		<property field="m_name" value="clement"/>
	</properties>
</component>

The defined type provides a service. Moreover it supports properties propagation. So all property, except listed one (m_name), will be published inside the provided services.
So create an instance of the Hello3 component type as follow:

-> create_conf  org.apache.felix.ipojo.example.ca.component.Hello3 
Insert the configuration : 
{service.factoryPid=org.apache.felix.ipojo.example.ca.component.Hello3}

Then, you can check provided services with the services 7 command

-> services 7 
// Factories and Managed Service factories // 
---- 
factory.name = org.apache.felix.ipojo.example.ca.component.Hello3 
instance.name = 
org.apache.felix.ipojo.example.ca.component.Hello3.a5ca5901-6e20-4636-8805-fbca2db1d68b 
objectClass = org.apache.felix.ipojo.example.ca.service.Hello 
service.factoryPid = org.apache.felix.ipojo.example.ca.component.Hello3 
service.id = 69 
->

Now, we update the instance configuration with a new property 'p1':

-> update_conf 
org.apache.felix.ipojo.example.ca.component.Hello3.a5ca5901-6e20-4636-8805-fbca2db1d68b p1=v1 
Update the configuration : {p1=v1} 
-> services 7 
config.admin.tutorial (7) provides: 
// Factories and Managed Service factories // 
---- 
factory.name = org.apache.felix.ipojo.example.ca.component.Hello3 
instance.name = 
org.apache.felix.ipojo.example.ca.component.Hello3.a5ca5901-6e20-4636-8805-fbca2db1d68b 
objectClass = org.apache.felix.ipojo.example.ca.service.Hello 
p1 = v1 
service.factoryPid = org.apache.felix.ipojo.example.ca.component.Hello3 
service.id = 69

Remark that the new property p1 is published.
Now we can remove this property by reconfiguring the instance with an empty configuration:

-> update_conf 
org.apache.felix.ipojo.example.ca.component.Hello3.a5ca5901-6e20-4636-8805-fbca2db1d68b 
Update the configuration : {} 
-> services 7 
ConfigAdminExample (8) provides: 
// Factories and Managed Service factories // 
---- 
factory.name = org.apache.felix.ipojo.example.ca.component.Hello3 
instance.name = 
org.apache.felix.ipojo.example.ca.component.Hello3.a5ca5901-6e20-4636-8805-fbca2db1d68b 
objectClass = org.apache.felix.ipojo.example.ca.service.Hello 
service.factoryPid = org.apache.felix.ipojo.example.ca.component.Hello3 
service.id = 69

The service does no more publish the p1 property.

Conclusion

This page has presented how to combine the configuration admin and iPOJO. You can also use FileInstall in combination with iPOJO and the Configuration Admin. Subscribe to the Felix users mailing list by sending a message to users-subscribe@felix.apache.org; after subscribing, email questions or feedback to users@felix.apache.org

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