Instance Controller or Service Controller ?

When the component implementation needs to impact the instance container, it uses controllers on Boolean fields. iPOJO provides two controllers:

This page explains the differences between the two kinds of controllers.

The Instance Lifecycle Controller

The instance lifecycle controller impacts the instance state. Such controller must only be used if the instance code has detected an irremediable situation, where the instance cannot behave correctly.

Such controller is generally used when the component code:

Instance Lifecycle Controller cannot be initialized, and generally are only set to false:

public class MyComponent {

    private boolean controller;

    public void setMyProperty(String value) {
        if (! ACCEPTABLE_VALUES.contains(value) {
                // Let's image that if the given 
                // value is not acceptable, we invalidate
                // the instance
                controller = false;

When set to false:

The service lifecycle controller

The service lifecycle controller impacts only the services exposed by the instance. It is used when the component implementation decides whether or not to publish the services.

Unlike the instance lifecycle controller, such controller can:

The following example publishes the component's provided service only after initialization.

public class MyComponent implements MyService {

    // Service not published by default
    private boolean controller;

    public void initialize() {
        // publish the service once the initialization
        // is completed.
        controller = true;

When the controller is set to true, the @PostRegistration callback is called. When it is set to false the @PostUnregistration callback is called. In both cases, the service is already registered or unregistered when the callback is invoked.

Notice that a @ServiceController controls all exposed services by default, but can be restricted to specific service interface with the specification attribute.