Wednesday, April 1, 2009

iPOJO and File Install : configuring iPOJO instances with 'cfg' files

FileInstall is a great bundle to provision your system. It watches a directory and installs every bundles contained inside the directory. Moreover, it’s fully support the configuration admin. So, it reads .cfg files contained in the folder and pushes the read configuration into the configuration admin.

iPOJO also supports the configuration admin. iPOJO instances can be created, deleted and reconfigured from the configuration admin.

So, why not creating, reconfiguring and deleting iPOJO instances from the cfg files.

File Install philosophy

File install is great and simple. It just has one general idea to understand:

The content of the watched folder is your system configuration

So, if you create cfg files inside this folder, those files will be analyzed and the configuration pushed in the configuration admin. To remove the configuration, just remove the file from the folder!

Note: Don’t forget to install the configuration admin

Using File install to create instances

When you declare an iPOJO component, this will expose a ManagedServiceFactory service. [Except if you voluntary set the component type to private]. This service can be used to create / reconfigure/ delete instances of this component type.

So, let’s say that we have the following bar.Foo class:

public class Foo {
private String name;


This declare an iPOJO component type (named bar.Foo (i.e. the classname) as no name is specified). This component type also declares a property (name).

So, once deployed, iPOJO will exposed a ManagedServiceFactory service with the ‘bar.Foo’ service pid. The configuration admin will push all matching configuration to this ManagedServiceFactory.

Now, let’s say that File install watches the ‘load’ folder. If you create a file named bar.Foo-1.cfg containing the following content:
name = the name
Once saved, File Install will find it, analyzes it and pushes the configuration to the configuration admin. The configuration admin will pushes this configuration to our ManagedServiceFactory, and so we just create an instance of our type!

So, cfg files completely replaces the tag of iPOJO metadata files. You no more need them (if you use annotations).

Let’s create a second file named bar.Foo-2.cfg containing the following content:
name = the second name
This will create another instance.

Reconfiguring an instance

To reconfigure an instance, just edit the cfg file. For example, edit the bar.Foo-2.cfg and change the name property to ‘a third name’. The instance will be automatically reconfigured.

Deleting an instance

To delete an instance, just remove the cfg file (containing the instance configuration) from the file install folder. That’s it! The watched folder is your system configuration.

The ManagedService case

So, let’s imagine that you don’t want to create instances from cfg file but just reconfiguring them. It’s also possible. File install also supports Managed Service, and so, will pushed a Managed Service configuration inside the configuration admin.

If you use this way, you have to create the instance yourself (from the metadata.xml file for example).
First, let’s modify our component type:

public class Foo {
private String name;


and create the metadata.xml file declaring an instance of this type:

<instance component="bar.Foo"/>

The “managedservice” attribute of the @Component annotation allows setting the service pid of the Managed Service. So, iPOJO will expose a ManagedService allowing reconfiguring your instance with the “MyPID” pid. [You can also set the managedservice pid from the instance configuration].
So, to reconfigure the instance, create a cfg file named MyPID.cfg containing the configuration such as:
name = a name

When you save the file in the watched folder, File install will pushes the configuration to the configuration admin. Then, the configuration admin will look for the matching ManagedService (the one with the MyPID and pushed the configuration. So, your instance will receives the configuration!

To edit the configuration, just edit the cfg file. To remove it, just remove the file from the folder.


File install is definitely a great tool to provision your system. The configuration admin supports can be useful to create iPOJO applications “on the fly” and will allows you reconfiguring your system dynamically!

No comments: