| <html><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Dependency Types</title><meta content="DocBook XSL Stylesheets V1.76.0" name="generator"><link rel="home" href="index.html" title="Virgo Programmer Guide"><link rel="up" href="ch03.html" title="Chapter 3. Deployment Architecture"><link rel="prev" href="ch03.html" title="Chapter 3. Deployment Architecture"><link rel="next" href="ch03s03.html" title="Regions"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table summary="Navigation header" width="100%"><tr><td align="left" width="20%"><a accesskey="p" href="ch03.html">Prev</a> </td><th align="center" width="60%"> </th><td align="right" width="20%"> <a accesskey="n" href="ch03s03.html">Next</a></td></tr></table><hr></div><div class="section" title="Dependency Types"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="architecture-dependency-types"></a>Dependency Types</h2></div></div></div><p> | |
| In an OSGi environment, there are two kinds of dependencies between various bundles: | |
| <span class="emphasis"><em>type</em></span> dependency and <span class="emphasis"><em>service</em></span> dependency. | |
| </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> | |
| <span class="bold"><strong>Type dependency</strong></span>: A bundle may depend on a | |
| type exported by another bundle thus creating a type dependency. Type | |
| dependencies are managed through <code class="literal">Import-Package</code> and | |
| <code class="literal">Export-Package</code> directives in the OSGi manifest. This | |
| kind of dependency is similar to a JAR file using types in other JAR files | |
| from the classpath. However, as we’ve seen earlier, there are | |
| significant differences. | |
| </p></li><li class="listitem"><p> | |
| <span class="bold"><strong>Service dependency</strong></span>: A bundle may also | |
| publish services (preferably using Spring-DM), and other bundles may consume | |
| those services. If two bundles depend on the same service, both will be | |
| communicating effectively to the same object. More specifically, any state | |
| for that service will be shared between all the clients of that service. | |
| This kind of arrangement is similar to the commonly seen client-server | |
| interaction through mechanisms such as RMI or Web Services. | |
| </p></li></ul></div><p> | |
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