Page History

...

This page presents how to use the iPOJO runtime and its associated service component model. The concepts of the service component model are introduced, followed by a simple example that demonstrates the features of iPOJO. This tutorial uses XML to describe components, however. However, iPOJO also supports annotations and provides an a Java API for this purpose.

Introduction

iPOJO aims to simplify service-oriented programming on OSGi frameworks; the name iPOJO is an abbreviation for injected POJO. iPOJO provides a new way to develop OSGi service components with the main goal being to simplify , simplifying service component implementation by transparently managing the dynamics of the environment as well as other non-functional requirements. The iPOJO framework allows developers to more clearly separate functional code (i.e., the POJOPOJOs) from the non-functional code (i.e., dependency management, service provision, configuration, etc.). At run time, iPOJO combines the functional and non-functional aspects at run time. To achieve this, iPOJO provides a simple and extensible service component model based on POJOs.

The POJO concept

"POJO" is just an acronym for Plain Old Java Object, but it embodies a concept that the simpler and less intrusive the design of a given framework, the better. The name is used to emphasize that a given object is not somehow special, but is an ordinary Java Object. Martin Fowler, Rebecca Parsons and Josh Mackenzie coined the term POJO in September 2000: "We wondered why people were so against using regular objects in their systems and concluded that it was because simple objects lacked a fancy name. So we gave them one, and it's caught on very nicely." From the a developer's perspective, the iPOJO framework strives as much as possible to only require POJOs in as much as it is possible.

iPOJO service component overview

A service component is able to provide and/or require services, where a service is an object that implements a given service interface embodied as a Java interface. In addition, iPOJO introduces a callback concept to notify a component about various state changes.

The component is the a central concept in iPOJO. In the core iPOJO model, a component describes service dependencies, provided services, and callbacks; this information is recorded in the component's metadata. ThenAfter components, the second next most important concept in iPOJO is the component instancesinstance. A component instances instance is a special version of the a component. By merging component metadata and instance configuration, the iPOJO runtime is able to manage the component, i.e., manage its life cycle, discover and inject required services, publish provided services, discover needed servicesand manage the component's life cycle.

A simple example

In this tutorial we will present how to:

...