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<?xml version="1.0" encoding="ISO-8859-1"?>
<document>
<properties>
<title>jSLP-OSGi - Java SLP (Service Location Protocol) Implementation for OSGi. Getting started with jSLP-OSGi</title>
<author email="rellermeyer_AT_inf.ethz.ch">Jan S. Rellermeyer</author>
</properties>
<meta name="keyword" content="Java, SLP, jSLP, Service Location Protocol, OSGi, Userguide"/>
<meta name="description" content="jSLP is a pure Java implementation of RFC 2608 (SLP, Service Location Protocol, Version 2) with a RFC 2614 style API. It can be both SLP UserAgent (UA) and ServiceAgent (SA). jSLP-OSGi integrates SLP with OSGi (Open Service Gateway Initiative)."/>
<meta http-equiv="cache-control" content="no-cache"/>
<meta http-equiv="pragma" content="no-cache"/>
<meta http-equiv="robots" content="index, follow"/>
<body>
<section name="Getting started with jSLP-OSGi">
<p>
jSLP OSGi registers <code>ch.ethz.iks.slp.ServiceLocationManager</code> as <code>ServiceFactory</code>.
The registered services are <code>ch.ethz.iks.slp.Advertiser</code> and <code>ch.ethz.iks.slp.Locator</code>
and every bundle requesting one of the services will get their own instance. Since requests for
<code>ServiceReferences</code> cannot pass parameters to the <code>ServiceFactory</code>,
the <code>Advertiser</code> and <code>Locator</code> instances will be created with the empty default
<code>Locale</code> and both classes have a setter method <code>.setLocale(Locale locale)</code> to change
the locale at runtime (this differs from the jSLP standalone version).
</p>
<p>
The following example shows how to get <code>Advertiser</code> and <code>Locator</code> instances and use them:
<source>
public class SLPTestBundle implements BundleActivator {
public void start(BundleContext context) throws Exception {
ServiceReference advRef = context.getServiceReference("ch.ethz.iks.slp.Advertiser");
ServiceReference locRef = context.getServiceReference("ch.ethz.iks.slp.Locator");
if (advRef != null) {
System.out.println("Got reference for Advertiser");
Advertiser advertiser = (Advertiser) context.getService(advRef);
advertiser.register(new ServiceURL("service:osgi:test://192.168.24.118", 20), null);
}
if (locRef != null) {
System.out.println("Got reference for Locator");
Locator locator = (Locator) context.getService(locRef);
ServiceLocationEnumeration slenum = locator.findServices(new ServiceType("service:osgi"), null, null);
System.out.println("RESULT:");
while (slenum.hasMoreElements()) {
System.out.println(slenum.nextElement());
}
}
}
public void stop(BundleContext context) throws Exception {
}
}
</source>
</p>
<p>
jSLP OSGi does not require <code>org.osgi.service.log</code> to run but if a bundle is present that provides this service,
jSLP OSGi makes use of it. If the service is not present, trace options passed by properties have no effect. jSLP-OSGi has
been successfully tested with <a href="http://flowsgi.inf.ethz.ch/concierge.html">Concierge OSGi</a>,
<a href="http://www.knopflerfish.org">Knopflerfish</a>, <a href="http://oscar.objectweb.org">Oscar</a> and
<a href="http://www.eclipse.org/equinox/">Eclipse Equinox</a>.
</p>
<p>
For developing Eclipse Plugins, it is recommended to checkout the jSLP-OSGi project from the
<a href="source-repository.html">subversion repository</a>. This project is already an Eclipse Plugin and
can be used as dependency for your own project. Unfortunately, Eclipse does not show the exception that is thrown
when jSLP runs on a linux box as non-root user and it tries to open port 427. Instead, it will print a plain
<code>ExceptionInInitializer</code>. The result is a general unavailability of the requested Locator or Advertiser instance.
</p>
<p>
Furthermore, Eclipse uses a resolving and starting strategy which is different from traditional OSGi. jSLP has
<code>Eclipse-LazyStart</code> set so it is started whenever a class from the bundle is accessed. This somewhat collides
with the OSGi service model where bundles are completely decoupled. So in the above example, jSLP as a Plugin is never
started and no Advertiser or Locator instance can be retrieved. To prevent this, simple use
<source>
ServiceReference advRef = context.getServiceReference(Advertiser.class.getName());
</source>
The call to the static field <code>class</code> will force the resolving of <code>ch.ethz.slp.Advertiser</code>,
the Plugin will be started and thus the ServiceFactory registered with the OSGi registry. (The same indeed works
for the Locator)
</p>
<p>
For debugging, jSLP-OSGi features the <code>ch.ethz.iks.slp.debug</code> property. If set to <code>true</code>
and a LogService is present, jSLP-OSGi prints additional information about internal state changes which makes it
easier to debug applications.
</p>
</section>
</body>
</document>
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