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    <p>"Components" are less formally defined than services.</p> <p>A service is <em>any object</em> that is registered in the OSGi Service Registry and can be looked up using its interface name(s). The only prerequisite is that a service should implement some interface... any interface. For example I could register a runnable object under the <code>java.lang.Runnable</code> interface, and clients could look it up using that interface name.</p> <p>A "component" tends to be an object whose lifecycle is managed, usually by a component framework such as Declarative Services (DS), Blueprint or iPOJO. See <a href="http://wiki.osgi.org/wiki/Component_Models_Overview" rel="noreferrer">this page</a> on the OSGi Community Wiki for a discussion of the different component frameworks available.</p> <p>A component may have any of the following features, in combination or alone:</p> <ul> <li>A component may be <em>started</em> and <em>stopped</em>; this would be considered an "active" component, though that is also an informal term. A component that doesn't need to be started or stopped is called passive.</li> <li>A component may <em>publish</em> itself as an OSGi service.</li> <li>A component may <em>bind to</em> or <em>consume</em> OSGi services.</li> </ul> <p>In general, using a component framework is the easiest way to work with OSGi services because the framework will manage the binding to the services that you want to consume. For example you could say that your component "depends on" a particular service, in which case the component will only be created and activated when that service is available -- and also it will be destroyed when the service becomes unavailable.</p>
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    1. USNeil Bartlett
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    1. COcould you provide an example of a component that is not a service?
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      1. USsantiagozky
    2. CO@santiagozky Sure. Suppose you want to a write Server component that sits on socket and responds to requests over TCP/IP. When the component starts, it opens the socket and creates the thread(s) required to serve clients. When it stops, it closes the thread(s) and socket. Another example: a component that creates a GUI using Swing, SWT or JavaFX. Neither of these example components are services themselves, though they may *use* services published by other components.
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    3. CO@neal, thanks. I get it now.
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