If you're a Java developer, you've almost certainly heard of OSGi and also heard that it's becoming quite a big deal. But you may still be wondering exactly "What is OSGi " Simply put, OSGi is a technology that allows you to create highly modular Java applications. It introduces a logical and physical module format, called a bundle, for explicitly structuring your application as a set of interconnected modules. OSGi lets you install, start, stop, update, or uninstall modules at execution time without taking down your entire system. In addition, OSGi defines a local service-oriented approach for creating applications out of loosely coupled components. With the prevalence of modern component and service-based architectures, OSGi is becoming increasingly important. It meshes well with such approaches and greatly simplifies their creation and management. It's the backbone of Eclipse's plugin system as well as many recent JavaEE containers, such as GlassFish v3, WebSphere v6.1, and WebLogic Event Server. Even the SpringSource Application Platform is built on top of it. OSGi in Action is a comprehensive guide to OSGi with two primary goals. First, it provides a clear introduction to OSGi concepts with examples that are relevant both for architects and developers. The central idea of OSGi is modularity, so you start by learning about OSGi bundles. You'll then see how OSGi handles module lifecycles and follow up with how it promotes service-oriented interaction among application components. With the core concepts well in hand, you'll explore numerous application scenarios and techniques. How much of OSGi do you actually need How do you embed OSGi inside other containers What are the best practices for migrating legacy systems to OSGi How can you embrace and make the most of system dynamism Expert authors Richard S. Hall, Karl Pauls, and Stuart McCulloch have years of experience both in building OSGi-based systems and in contributing to OSGi implementations such as Apache Felix.