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27 <div class="main">
28<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-ApacheFelixFrameworkLaunchingandEmbedding"></a>Apache Felix Framework Launching and Embedding</h1>
29
30<p><em>[This document is based on Felix 1.4.0.]</em></p>
31
32<ul>
33 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-introduction" title="introduction on Apache Felix Framework Launching and Embedding">Introduction</a></li>
34 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-overview" title="overview on Apache Felix Framework Launching and Embedding">API Overview</a>
35 <ul>
36 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-creatingandconfiguring" title="creating-and-configuring on Apache Felix Framework Launching and Embedding">Creating and Configuring the Framework Instance</a></li>
37 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-startinginstance" title="starting-instance on Apache Felix Framework Launching and Embedding">Starting the Framework Instance</a></li>
38 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-stoppinginstance" title="stopping-instance on Apache Felix Framework Launching and Embedding">Stopping the Framework Instance</a></li>
39 </ul>
40 </li>
41 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-launching" title="launching on Apache Felix Framework Launching and Embedding">Launching Felix</a>
42 <ul>
43 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-standardlauncher" title="standard-launcher on Apache Felix Framework Launching and Embedding">Standard Felix Launcher</a></li>
44 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-customlauncher" title="custom-launcher on Apache Felix Framework Launching and Embedding">Custom Felix Launcher</a></li>
45 </ul>
46 </li>
47 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-embedding" title="embedding on Apache Felix Framework Launching and Embedding">Embedding Felix</a>
48 <ul>
49 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction" title="host-interaction on Apache Felix Framework Launching and Embedding">Host/Felix Interaction</a></li>
50 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostservices" title="host-services on Apache Felix Framework Launching and Embedding">Providing Host Application Services</a></li>
51 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostserviceusage" title="host-service-usage on Apache Felix Framework Launching and Embedding">Using Services Provided by Bundles</a>
52 <ul>
53 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-servicereflection" title="service-reflection on Apache Felix Framework Launching and Embedding">Using Bundle Services via Reflection</a></li>
54 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-serviceother" title="service-other on Apache Felix Framework Launching and Embedding">Other Approaches</a></li>
55 </ul>
56 </li>
57 </ul>
58 </li>
59 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-caveat" title="caveat on Apache Felix Framework Launching and Embedding">Caveat</a></li>
60 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-feedback" title="feedback on Apache Felix Framework Launching and Embedding">Feedback</a></li>
61</ul>
62
63
64<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-introduction"></a></p>
65
66<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-Introduction"></a>Introduction</h1>
67
68<p>The Apache Felix framework is intended to be easily launchable and
69embeddable. For example, Felix avoids the use of system properties for
70configuration, since these are globals and can cause interference if
71multiple framework instances are created in the same VM. Felix also
72tries to multiplex singleton facilities, like the URL stream handler
73factory. The goal is to make it possible to use Felix in as many
74scenarios as possible; however, this is still just a goal. In other
75words, this is a work in progress and if any issues arise, it would be
76greatly appreciated if they are brought to the attention of the Felix
77community. The next section provides a Felix API overview, while the
78remainder of the document is divided into two sections, one focusing on
79how to launch Felix and one focusing on how to embed Felix into a host
80application.</p>
81
82<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-overview"></a></p>
83
84<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-APIOverview"></a>API Overview</h1>
85
86<p>The Felix framework is implemented by the <tt>org.apache.felix.framework.Felix</tt> class or just <tt>Felix</tt>
87for short. As part of the ongoing OSGi specification process, there is
88a movement to standardize the API for launching and embedding OSGi
89framework implementations. The approach is to have the framework
90implement the <tt>org.osgi.framework.launch.Framework</tt> interface, which extends the <tt>org.osgi.framework.Bundle</tt> interface. These interfaces provide the necessary means to launch and manage framework instances. The <tt>Bundle</tt> interface is defined as:</p>
91
92<div class="code"><div class="codeContent">
93<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> Bundle
94{
95 BundleContext getBundleContext();
96 <span class="code-object">long</span> getBundleId();
97 URL getEntry(<span class="code-object">String</span> name);
98 Enumeration getEntryPaths(<span class="code-object">String</span> path);
99 Enumeration findEntries(<span class="code-object">String</span> path, <span class="code-object">String</span> filePattern, <span class="code-object">boolean</span> recurse);
100 Dictionary getHeaders();
101 Dictionary getHeaders(<span class="code-object">String</span> locale);
102 <span class="code-object">long</span> getLastModified();
103 <span class="code-object">String</span> getLocation();
104 URL getResource(<span class="code-object">String</span> name);
105 Enumeration getResources(<span class="code-object">String</span> name) <span class="code-keyword">throws</span> IOException;
106 ServiceReference[] getRegisteredServices();
107 ServiceReference[] getServicesInUse();
108 <span class="code-object">int</span> getState();
109 <span class="code-object">String</span> getSymbolicName();
110 <span class="code-object">boolean</span> hasPermission(<span class="code-object">Object</span> obj);
111 <span class="code-object">Class</span> loadClass(<span class="code-object">String</span> name) <span class="code-keyword">throws</span> ClassNotFoundException;
112 void start() <span class="code-keyword">throws</span> BundleException;
113 void stop() <span class="code-keyword">throws</span> BundleException;
114 void uninstall() <span class="code-keyword">throws</span> BundleException;
115 void update() <span class="code-keyword">throws</span> BundleException;
116 void update(InputStream is) <span class="code-keyword">throws</span> BundleException;
117}</pre>
118</div></div>
119
120<p>The <tt>Framework</tt> interface is defined as:</p>
121
122<div class="code"><div class="codeContent">
123<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> Framework <span class="code-keyword">extends</span> Bundle
124{
125 void init();
126 FrameworkEvent waitForStop();
127}</pre>
128</div></div>
129
130<p>An additional requirement for framework implementations not captured
131in the interface definitions is that they must implement a public
132constructor that accepts a <tt>Map</tt>, which is used to pass in configuration properties. When you instantiate the <tt>Felix</tt>
133class, the resulting object is the actual System Bundle that bundles
134inside the framework will see if they get bundle 0, which is the System
135Bundle as defined by the OSGi specification.</p>
136
137<table class="warningMacro" align="center" border="0" cellpadding="5" cellspacing="8" width="85%"><colgroup><col width="24"><col></colgroup><tbody><tr><td valign="top"><img src="apache-felix-framework-launching-and-embedding_files/forbidden.gif" alt="" align="absmiddle" border="0" height="16" width="16"></td><td><b class="strong">WARNING</b><br>
138<p>This API is undergoing changes and is not completely finalized, so future changes are possible.</p></td></tr></tbody></table>
139
140<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-creatingandconfiguring"></a></p>
141
142<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-CreatingandConfiguringtheFrameworkInstance"></a>Creating and Configuring the Framework Instance</h2>
143
144<p>To create a framework instance, simply instantiate the <tt>Felix</tt> class. A newly created framework instance is in the <tt>Bundle.INSTALLED</tt> state. You configure the instance by passing the constructor a <tt>Map</tt> containing its configurations properties. The configuration map may contain the following OSGi standard properties:</p>
145
146<ul>
147 <li><tt>org.osgi.framework.system.packages</tt> - specifies a
148list of packages the system bundle should export from the environment;
149if this is not set, then the framework uses a reasonable default fault.</li>
150 <li><tt>org.osgi.framework.system.packages.extra</tt>
151- specifies a list of additional packages the system bundle should
152export from the environment that are appended to the packages specified
153in <tt>org.osgi.framework.system.packages</tt>; there is no default value for this property.</li>
154 <li><tt>org.osgi.framework.bootdelegation</tt>
155- specifies a list of packages that should be made implicitly available
156to all bundles from the environment (i.e., no need to import them);
157there is no default value for this property and its use should be
158avoided.</li>
159 <li><tt>org.osgi.framework.storage</tt> - specifies the
160path to a directory, which will be created if it does not exist, to use
161for bundle cache storage; the default value for this property is "<tt>felix-cache</tt>" in the current working directory.</li>
162 <li><tt>org.osgi.framework.storage.clean</tt>
163- specifies whether the bundle cache should be flushed; the default
164value for this property is "none", but it can be changed to
165"onFirstInit" to flush the bundle cache when the framework is
166initialized.</li>
167 <li><tt>org.osgi.framework.startlevel</tt> - specifies the start level the framework enters upon startup; the default value for this property is 1.</li>
168</ul>
169
170
171<p>Felix also has the following, non-standard configuration properties:</p>
172
173<ul>
174 <li><tt>felix.cache.rootdir</tt> - specifies which directory should be used to calculate absolute paths when relative paths are used for the <tt>org.osgi.framework.storage</tt> property; the default value for this property is the current working directory.</li>
175 <li><tt>felix.systembundle.activators</tt> - specifies a <tt>List</tt> of <tt>BundleActivator</tt>
176instances that are started/stopped when the System Bundle is
177started/stopped; the specified instances will receive the System
178Bundle's <tt>BundleContext</tt> when invoked.</li>
179 <li><tt>felix.log.logger</tt> - specifies an instance of <tt>org.apache.felix.framework.util.Logger</tt> that the framework uses as its default logger.</li>
180 <li><tt>felix.log.level</tt> - specifies an integer <tt>String</tt>
181whose value indicates the degree of logging reported by the framework;
182the default value is "1" and "0" turns off logging completely,
183otherwise log levels match those specified in the OSGi Log Service
184(i.e., 1 = error, 2 = warning, 3 = information, and 4 = debug).</li>
185 <li><tt>felix.startlevel.bundle</tt> - specifies the start level for newly installed bundles; the default value is 1.</li>
186 <li><tt>framework.service.urlhandlers</tt>
187- specifies whether or not to activate the URL Handlers service for the
188framework instance; the default value is "&lt;tt&gt;true&lt;/tt&gt;",
189which results in the
190&lt;tt&gt;URL.setURLStreamHandlerFactory()&lt;/tt&gt; and
191&lt;tt&gt;URLConnection.setContentHandlerFactory()&lt;/tt&gt; being
192called.</li>
193</ul>
194
195
196<p>The configuration map passed into the constructor is copied and the
197keys are treated as case insensitive. You are not able to change the
198framework's configuration after construction. If you need a different
199configuration, you must create a new framework instance.</p>
200
201<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-startinginstance"></a></p>
202
203<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StartingtheFrameworkInstance"></a>Starting the Framework Instance</h2>
204
205<p>The <tt>start()</tt> method is used to start the framework instance. If the <tt>init()</tt> method was not invoked prior to calling <tt>start()</tt>, then it is implicitly invoked from <tt>start()</tt>. The two methods result in two different framework state transitions:</p>
206
207<ul>
208 <li><tt>init()</tt> results in the framework instance in the <tt>Bundle.STARTING</tt> state.</li>
209 <li><tt>start()</tt> results in the framework instance in the <tt>Bundle.ACTIVE</tt> state.</li>
210</ul>
211
212
213<p>The <tt>init()} method is necessary since the framework does not have a {{BundleContext</tt> when it is first created, so a transition to the <tt>Bundle.STARTING</tt> state is required to acquire its context (via <tt>Bundle.getBundleContext()</tt>) for performing various tasks, such as installing bundles. Note that Felix also provides the <tt>felix.systembundle.activators</tt> property that serves a similar purpose. After the <tt>init()</tt> method completes, the follow actions have been performed:</p>
214
215<ul>
216 <li>Event handling is enabled.</li>
217 <li>The security manager is installed if it is enabled.</li>
218 <li>The framework is set to start level 0.</li>
219 <li>All bundles in the bundle caches are reified and their state is set to <tt>Bundle.INSTALLED</tt>.</li>
220 <li>The framework gets a valid <tt>BundleContext</tt>.</li>
221 <li>All framework-provided services are made available (e.g., PackageAdmin, StartLevel, etc.).</li>
222 <li>The framework enters the <tt>Bundle.STARTING</tt> state.</li>
223</ul>
224
225
226<p>A call to <tt>start()</tt> is necessary to start the framework instance, if the <tt>init()</tt> method is invoked manually. Invoking <tt>init()</tt> or <tt>start()</tt> on an already started framework as no effect.</p>
227
228<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-stoppinginstance"></a></p>
229
230<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StoppingtheFrameworkInstance"></a>Stopping the Framework Instance</h2>
231
232<p>To stop the framework instance, invoke the <tt>stop()</tt> method, which will asynchronously stop the framework. To know when the framework has finished its shutdown sequence, use the <tt>waitForStop()</tt> method to wait until it is complete. A stopped framework will be in the <tt>Bundle.RESOLVED</tt> state. It is possible to restart the framework, using the normal combination of <tt>init()</tt>/<tt>start()</tt> methods as previously described.</p>
233
234<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-launching"></a></p>
235
236<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-LaunchingFelix"></a>Launching Felix</h1>
237
238<p>Launching Felix is fairly simple and involves only three steps:</p>
239
240<ol>
241 <li>Define some configuration properties.</li>
242 <li>Create an instance of <tt>org.apache.felix.framework.Felix</tt> with the configuration properties.</li>
243 <li>Invoke the <tt>org.apache.felix.framework.Felix.start()</tt> method.</li>
244</ol>
245
246
247<p>In reality, the first step is optional, since all properties will
248have reasonable defaults, but if you are creating a launcher you will
249generally want to more than that, such as automatically installing and
250starting bundles when you start the framework instance. The default
251Felix launcher defines reusable functionality to automatically install
252and/or start bundles upon framework startup; see the <a href="http://felix.apache.org/site/apache-felix-usage-documentation.html#ApacheFelixUsageDocumentation-configuringfelix" title="configuring-felix on Apache Felix Usage Documentation">usage document</a> for more information on configuring Felix and on the various configuration properties.</p>
253
254<p>The remainder of this section describes how the standard Felix
255launcher works as well as how to create a custom launcher for Felix.</p>
256
257<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-standardlauncher"></a></p>
258
259<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StandardFelixLauncher"></a>Standard Felix Launcher</h2>
260
261<p>The standard Felix launcher is very simple and is not intended to
262solve every possible requirement; it is intended to work for most
263standard situations. Most special launching requirements should be
264resolved by creating a custom launcher. This section describes how the
265standard launcher works. The following code represents the complete <tt>main()</tt> method of the standard launcher, each numbered comment will be described in more detail below:</p>
266
267<div class="code"><div class="codeContent">
268<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">static</span> void main(<span class="code-object">String</span>[] argv) <span class="code-keyword">throws</span> Exception
269{
270 <span class="code-comment">// (1) Check <span class="code-keyword">for</span> proper command line usage.
271</span> <span class="code-keyword">if</span> (args.length &gt; 1)
272 {
273 <span class="code-object">System</span>.out.println(<span class="code-quote">"Usage: [&lt;bundle-cache-dir&gt;]"</span>);
274 <span class="code-object">System</span>.exit(0);
275 }
276
277 <span class="code-comment">// (2) Load system properties.
278</span> Main.loadSystemProperties();
279
280 <span class="code-comment">// (3) Read configuration properties.
281</span> Properties configProps = Main.loadConfigProperties();
282
283 <span class="code-comment">// (4) Copy framework properties from the system properties.
284</span> Main.copySystemProperties(configProps);
285
286 <span class="code-comment">// (5) If specified, use command-line argument as path to bundle cache.
287</span> <span class="code-keyword">if</span> (args.length &gt; 0)
288 {
289 configProps.setProperty(Constants.FRAMEWORK_STORAGE, args[0]);
290 }
291
292 <span class="code-comment">// (6) Create a list <span class="code-keyword">for</span> custom framework activators and
293</span> <span class="code-comment">// add an instance of the auto-activator it <span class="code-keyword">for</span> processing
294</span> <span class="code-comment">// auto-install and auto-start properties. Add <span class="code-keyword">this</span> list
295</span> <span class="code-comment">// to the configuration properties.
296</span> List list = <span class="code-keyword">new</span> ArrayList();
297 list.add(<span class="code-keyword">new</span> AutoActivator(configProps));
298 configProps.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
299
300 <span class="code-comment">// Print welcome banner.
301</span> <span class="code-object">System</span>.out.println(<span class="code-quote">"\nWelcome to Felix."</span>);
302 <span class="code-object">System</span>.out.println(<span class="code-quote">"=================\n"</span>);
303
304 <span class="code-keyword">try</span>
305 {
306 <span class="code-comment">// (7) Create an instance and start the framework.
307</span>
308 m_felix = <span class="code-keyword">new</span> Felix(configProps);
309 m_felix.start();
310 <span class="code-comment">// (8) Wait <span class="code-keyword">for</span> framework to stop to exit the VM.
311</span> m_felix.waitForStop();
312 <span class="code-object">System</span>.exit(0);
313 }
314 <span class="code-keyword">catch</span> (Exception ex)
315 {
316 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
317 ex.printStackTrace();
318 <span class="code-object">System</span>.exit(-1);
319 }
320}</pre>
321</div></div>
322
323<p>The general steps of the standard launcher are quite straightforward:</p>
324
325<ol>
326 <li>The launcher only supports a single, optional command-line
327argument, which is the path to the bundle cache, so check for this and
328issue a usage message it there are more than one arguments.</li>
329 <li>Load any system properties specified in the <tt>system.properties</tt> file; this file is typically located in the <tt>conf/</tt> directory of the Felix installation directory, but it can be specified directly using the <tt>felix.system.properties</tt>
330system property. This file is not needed to launch Felix and is
331provided merely for convenience when system properties must be
332specified. The file is a standard Java properties file, but it also
333supports property substitution using <tt>${&lt;property-name</tt>} syntax. Property substitution can be nested; only system properties will be used for substitution.</li>
334 <li>Load any configuration properties specified in the <tt>config.properties</tt> file; this file is typically located in the <tt>conf/</tt> directory of the Felix installation directory, but it can be specified directly using the <tt>felix.config.properties</tt>
335system property. This file is used to configure the Felix instance
336created by the launcher. The file is a standard Java properties file,
337but it also supports property substitution using "<tt>${&lt;property-name</tt>}"
338syntax. Property substitution can be nested; configuration and system
339properties will be used for substitution with configuration properties
340having precedence.</li>
341 <li>For convenience, any configuration
342properties that are set as system properties will be copied into the
343set of configuration properties to provide an easy way to add to or
344override configuration properties specified in the <tt>config.properties</tt> file.</li>
345 <li>If there is a single command-line argument, then use that to set the value of <tt>org.osgi.framework.storage</tt>; relative paths are relative to the current directory unless the <tt>felix.cache.rootdir</tt> property is set.</li>
346 <li>Create a list to hold custom framework activators and add an instance of <tt>org.apache.felix.main.AutoActivator</tt>, which will process <tt>felix.auto.install</tt> and <tt>felix.auto.start</tt> configuration properties during framework startup to automatically install and/or start bundles; see the <a href="http://felix.apache.org/site/apache-felix-usage-documentation.html#ApacheFelixUsageDocumentation-configuringfelix" title="configuring-felix on Apache Felix Usage Documentation">usage document</a> for more information configuration properties.</li>
347 <li>Create the Felix instance passing in the configuration properties, then call <tt>start()</tt>.</li>
348 <li>Invoke <tt>waitForStop()</tt> to wait for the framework to stop to force the VM to exit; this is necessary because the framework never calls <tt>System.exit()</tt> and some libraries (e.g., Swing) create threads that will not allow the VM to exit.</li>
349</ol>
350
351
352<p>The framework is not active until the <tt>start()</tt> method is
353called. If no shell bundles are installed and started or if there is
354difficulty locating the shell bundles specified in the auto-start
355property, then it will appear as if the framework is hung, but it is
356actually running without any way to interact with it since the shell
357bundles provide the only means of interaction.</p>
358
359<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-customlauncher"></a></p>
360
361<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-CustomFelixLauncher"></a>Custom Felix Launcher</h2>
362
363<p>This section creates a bare-bones launcher to demonstrate the
364minimum requirements for creating an interactive launcher for the Felix
365framework. This example uses the standard Felix shell bundles for
366interactivity, but any other bundles could be used instead. For
367example, the shell service and telnet bundles could be used to launch
368Felix and make it remotely accessible.</p>
369
370<p>This example launcher project has the following directory structure:</p>
371
372<div class="preformatted"><div class="preformattedContent">
373<pre>launcher/
374 lib/
375 org.apache.felix.main-1.4.0.jar
376 bundle/
377 org.apache.felix.shell-1.0.2.jar
378 org.apache.felix.shell.tui-1.0.2.jar
379 src/
380 example/
381 Main.java
382</pre>
383</div></div>
384
385<p>The <tt>lib/</tt> directory contains Felix' main JAR file, which
386also contains the OSGi core interfaces. The main JAR file is used so
387that we can reuse the default launcher's auto-install/auto-start
388configuration property handling; if these capabilities are not needed,
389then it would be possible to use the framework JAR file instead of the
390main JAR file. The <tt>bundle/</tt> directory contains the shell
391service and textual shell interface bundles that will be used for
392interacting with the framework instance. Note: If you do not launch
393Felix with interactive bundles, it will appear as if the framework
394instance is hung, but it is actually just sitting there waiting for
395someone to tell it to do something. The <tt>src/example/</tt> directory contains the following <tt>Main.java</tt> file, which is a very simplistic Felix launcher.</p>
396
397<div class="code"><div class="codeContent">
398<pre class="code-java"><span class="code-keyword">package</span> example;
399
400<span class="code-keyword">import</span> java.util.ArrayList;
401<span class="code-keyword">import</span> java.util.List;
402<span class="code-keyword">import</span> java.util.Map;
403<span class="code-keyword">import</span> java.util.HashMap;
404<span class="code-keyword">import</span> org.osgi.framework.Constants;
405<span class="code-keyword">import</span> org.apache.felix.framework.Felix;
406<span class="code-keyword">import</span> org.apache.felix.framework.util.FelixConstants;
407<span class="code-keyword">import</span> org.apache.felix.main.AutoActivator;
408
409<span class="code-keyword">public</span> class Main
410{
411 <span class="code-keyword">private</span> <span class="code-keyword">static</span> Felix m_felix = <span class="code-keyword">null</span>;
412
413 <span class="code-keyword">public</span> <span class="code-keyword">static</span> void main(<span class="code-object">String</span>[] argv) <span class="code-keyword">throws</span> Exception
414 {
415 <span class="code-comment">// Print welcome banner.
416</span> <span class="code-object">System</span>.out.println(<span class="code-quote">"\nWelcome to Felix."</span>);
417 <span class="code-object">System</span>.out.println(<span class="code-quote">"=================\n"</span>);
418
419 Map configMap = <span class="code-keyword">new</span> HashMap();
420 configMap.put(AutoActivator.AUTO_START_PROP + <span class="code-quote">".1"</span>,
421 <span class="code-quote">"file:bundle/org.apache.felix.shell-1.0.2.jar "</span> +
422 <span class="code-quote">"file:bundle/org.apache.felix.shell.tui-1.0.2.jar"</span>);
423 List list = <span class="code-keyword">new</span> ArrayList();
424 list.add(<span class="code-keyword">new</span> AutoActivator(configMap));
425 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
426
427 <span class="code-keyword">try</span>
428 {
429 m_felix = <span class="code-keyword">new</span> Felix(configMap);
430 m_felix.start();
431 m_felix.waitForStop();
432 <span class="code-object">System</span>.exit(0);
433 }
434 <span class="code-keyword">catch</span> (Exception ex)
435 {
436 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
437 ex.printStackTrace();
438 <span class="code-object">System</span>.exit(-1);
439 }
440 }
441}</pre>
442</div></div>
443
444<p>This launcher has all information hard coded in it, unlike the
445default Felix launcher, which loads configuration properties from files
446and performs variable substitution. This simple launcher provides a
447good starting point if the features of the default launcher are not
448necessary. Since very few configuration properties are specified, the
449default values are used. In the case of the framework bundle cache, it
450will use "<tt>felix-cache</tt>" in the current directory.</p>
451
452<p>By breaking down the above source code into small chunks, it is quite easy to see what is going on.</p>
453
454<div class="code"><div class="codeContent">
455<pre class="code-java">Map configMap = <span class="code-keyword">new</span> HashMap();</pre>
456</div></div>
457
458<p>This simply creates a map to hold configuration properties.</p>
459
460<div class="code"><div class="codeContent">
461<pre class="code-java">configMap.put(AutoActivator.AUTO_START_PROP + <span class="code-quote">".1"</span>,
462 <span class="code-quote">"file:bundle/org.apache.felix.shell-1.0.2.jar "</span> +
463 <span class="code-quote">"file:bundle/org.apache.felix.shell.tui-1.0.2.jar"</span>);</pre>
464</div></div>
465
466<p>This sets the <tt>AutoActivator.AUTO_START_PROP</tt> configuration property (string value "<tt>felix.auto.start</tt>"),
467which is a space-delimited list of bundle URLs that the framework will
468automatically install and start when the framework starts. However,
469this property key cannot be used as is; it must be appended with a "."
470and then a number, where the number represents the start level for the
471bundle when it is installed. In this particular example, ".1" is
472appended to the property name, thus the two bundles will be installed
473into start level one. This example uses relative <tt>file:</tt> URLs, which will load the bundles from the <tt>bundle/</tt>
474directory assuming that the launcher is started from the root directory
475of the launcher project. It is also possible to specify absolute URLs
476or remote URLs.</p>
477
478<div class="code"><div class="codeContent">
479<pre class="code-java">List list = <span class="code-keyword">new</span> ArrayList();
480 list.add(<span class="code-keyword">new</span> AutoActivator(configMap));
481 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);</pre>
482</div></div>
483
484<p>This above creates a list to hold custom framework activators and adds an instance of <tt>org.apache.felix.main.AutoActivator</tt>
485to it, which will process the auto-install and auto-start configuration
486properties during framework startup. The list of activators is then
487added to the configuration map.</p>
488
489<div class="code"><div class="codeContent">
490<pre class="code-java">m_felix = <span class="code-keyword">new</span> Felix(configMap);
491 m_felix.start();</pre>
492</div></div>
493
494<p>These steps create the framework instance and start it. The configuration property map is passed into the <tt>Felix</tt> constructor.</p>
495
496<div class="code"><div class="codeContent">
497<pre class="code-java">m_felix.waitForStop();
498 <span class="code-object">System</span>.exit(0);</pre>
499</div></div>
500
501<p>These final steps cause the launching application thread to wait for
502the framework to stop and when it does the launching thread calls <tt>System.exit()</tt> to make sure the VM actually exits.</p>
503
504<p>The following command compiles the launcher when run from the root directory of the launcher project:</p>
505
506<div class="preformatted"><div class="preformattedContent">
507<pre>javac -d . -classpath lib/org.apache.felix.main-1.4.0.jar src/example/Main.java
508</pre>
509</div></div>
510
511<p>After executing this command, an <tt>example/</tt> directory is
512created in the current directory, which contains the generated class
513file. The following command executes the simple launcher when run from
514the root directory of the launcher project:</p>
515
516<div class="preformatted"><div class="preformattedContent">
517<pre>java -cp .:lib/org.apache.felix.main-1.4.0.jar example.Main
518</pre>
519</div></div>
520
521<p>After executing this command, a "<tt>felix-cache/</tt>" directory is created that contains the installed bundles, which were installed from the <tt>bundle/</tt> directory.</p>
522
523<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-embedding"></a></p>
524
525<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-EmbeddingFelix"></a>Embedding Felix</h1>
526
527<p>Embedding Felix into a host application is a simple way to provide a
528sophisticated extensibility mechanism (i.e., a plugin system) to the
529host application. Embedding Felix is very similar to launching Felix as
530described above, the main difference is that the host application
531typically wants to interact with the framework instance and/or
532installed bundles/services from the outside. This is fairly easy to
533achieve with Felix, but there are some subtle issues to understand.
534This section presents the mechanisms for embedding Felix into a host
535application and the issues in doing so.</p>
536
537<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction"></a></p>
538
539<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-Host/FelixInteraction"></a>Host/Felix Interaction</h2>
540
541<p>In the section on <a href="#ApacheFelixFrameworkLaunchingandEmbedding-launching" title="launching on Apache Felix Framework Launching and Embedding">launching</a> Felix above, the <tt>Felix</tt> accepts a configuration property called <tt>felix.systembundle.activators</tt>,
542which is a list of bundle activator instances. These bundle activator
543instances provide a convenient way for host applications to interact
544with the Felix framework. The ability offered by these activators can
545also be accomplished by invoking <tt>init()</tt> on the framework instance and the using <tt>getBundleContext()</tt> to get the System Bundle's context, but it can be more convenient to use an activator instance.</p>
546
547<p>Each activator instance passed into the constructor effectively becomes part of the System Bundle. This means that the <tt>start()</tt>/<tt>stop()</tt> methods of each activator instance in the list gets invoked when the System Bundle's activator <tt>start()</tt>/<tt>stop()</tt> methods gets invoked, respectively. Each activator instance will be given the System Bundle's <tt>BundleContext</tt> object so that they can interact with the framework. Consider following snippet of a bundle activator:</p>
548
549<div class="code"><div class="codeContent">
550<pre class="code-java"><span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
551{
552 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
553
554 <span class="code-keyword">public</span> void start(BundleContext context)
555 {
556 m_context = context;
557 }
558
559 <span class="code-keyword">public</span> void stop(BundleContext context)
560 {
561 m_context = <span class="code-keyword">null</span>;
562 }
563
564 <span class="code-keyword">public</span> Bundle[] getBundles()
565 {
566 <span class="code-keyword">if</span> (m_context != <span class="code-keyword">null</span>)
567 {
568 <span class="code-keyword">return</span> m_context.getBundles();
569 }
570 <span class="code-keyword">return</span> <span class="code-keyword">null</span>;
571 }
572}</pre>
573</div></div>
574
575<p>Given the above bundle activator, it is now possible to embed Felix
576into a host application and interact with it as the following snippet
577illustrates:</p>
578
579<div class="code"><div class="codeContent">
580<pre class="code-java"><span class="code-keyword">public</span> class HostApplication
581{
582 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
583 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
584
585 <span class="code-keyword">public</span> HostApplication()
586 {
587 <span class="code-comment">// Create a configuration property map.
588</span> Map configMap = <span class="code-keyword">new</span> HashMap();
589 <span class="code-comment">// Create host activator;
590</span> m_activator = <span class="code-keyword">new</span> HostActivator();
591 List list = <span class="code-keyword">new</span> ArrayList();
592 list.add(m_activator);
593 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
594
595 <span class="code-keyword">try</span>
596 {
597 <span class="code-comment">// Now create an instance of the framework with
598</span> <span class="code-comment">// our configuration properties.
599</span> m_felix = <span class="code-keyword">new</span> Felix(configMap);
600 <span class="code-comment">// Now start Felix instance.
601</span> m_felix.start();
602 }
603 <span class="code-keyword">catch</span> (Exception ex)
604 {
605 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
606 ex.printStackTrace();
607 }
608 }
609
610 <span class="code-keyword">public</span> Bundle[] getInstalledBundles()
611 {
612 <span class="code-comment">// Use the system bundle activator to gain external
613</span> <span class="code-comment">// access to the set of installed bundles.
614</span> <span class="code-keyword">return</span> m_activator.getBundles();
615 }
616
617 <span class="code-keyword">public</span> void shutdownApplication()
618 {
619 <span class="code-comment">// Shut down the felix framework when stopping the
620</span> <span class="code-comment">// host application.
621</span> m_felix.stop();
622 m_felix.waitForStop();
623 }
624}</pre>
625</div></div>
626
627<p>Notice how the <tt>HostApplication.getInstalledBundles()</tt> method
628uses its activator instance to get access to the System Bundle's
629context in order to interact with the embedded Felix framework
630instance. This approach provides the foundation for all interaction
631between the host application and the embedded framework instance.</p>
632
633<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostservices"></a></p>
634
635<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-ProvidingHostApplicationServices"></a>Providing Host Application Services</h2>
636
637<p>Providing services from the host application to bundles inside the
638embedded Felix framework instance follows the basic approach laid out
639in <a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction" title="host-interaction on Apache Felix Framework Launching and Embedding">above</a>.
640The main complication for providing a host application service to
641bundles is the fact that both the host application and the bundles must
642be using the same class definitions for the service interface classes.
643Since the host application cannot import classes from a bundle, this
644means that the service interface classes <b>must</b> be accessible on
645the class path, typically as part of the host application itself. The
646host application then must export the service interface package via the
647system bundle so that bundles installed into the embedded framework
648instance can import it. This is achieved using the <tt>org.osgi.framework.system.packages.extra</tt> configuration property previously presented.</p>
649
650<p>Consider the follow simple property lookup service:</p>
651
652<div class="code"><div class="codeContent">
653<pre class="code-java"><span class="code-keyword">package</span> host.service.lookup;
654
655<span class="code-keyword">public</span> class Lookup
656{
657 <span class="code-keyword">public</span> <span class="code-object">Object</span> lookup(<span class="code-object">String</span> name);
658}</pre>
659</div></div>
660
661<p>This package is simply part of the host application, which is potentially packaged into a JAR file and started with the "<tt>java -jar</tt>"
662command. Now consider the following host application bundle activator,
663which will be used to register/unregister the property lookup service
664when the embedded framework instance starts/stops:</p>
665
666<div class="code"><div class="codeContent">
667<pre class="code-java"><span class="code-keyword">package</span> host.core;
668
669<span class="code-keyword">import</span> java.util.Map;
670<span class="code-keyword">import</span> org.osgi.framework.BundleActivator;
671<span class="code-keyword">import</span> org.osgi.framework.BundleContext;
672<span class="code-keyword">import</span> org.osgi.framework.ServiceRegistration;
673<span class="code-keyword">import</span> host.service.lookup;
674
675<span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
676{
677 <span class="code-keyword">private</span> Map m_lookupMap = <span class="code-keyword">null</span>;
678 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
679 <span class="code-keyword">private</span> ServiceRegistration m_registration = <span class="code-keyword">null</span>;
680
681 <span class="code-keyword">public</span> HostActivator(Map lookupMap)
682 {
683 <span class="code-comment">// Save a reference to the service's backing store.
684</span> m_lookupMap = lookupMap;
685 }
686
687 <span class="code-keyword">public</span> void start(BundleContext context)
688 {
689 <span class="code-comment">// Save a reference to the bundle context.
690</span> m_context = context;
691 <span class="code-comment">// Create a property lookup service implementation.
692</span> Lookup lookup = <span class="code-keyword">new</span> Lookup() {
693 <span class="code-keyword">public</span> <span class="code-object">Object</span> lookup(<span class="code-object">String</span> name)
694 {
695 <span class="code-keyword">return</span> m_lookupMap.get(name);
696 }
697 };
698 <span class="code-comment">// Register the property lookup service and save
699</span> <span class="code-comment">// the service registration.
700</span> m_registration = m_context.registerService(
701 Lookup.class.getName(), lookup, <span class="code-keyword">null</span>);
702 }
703
704 <span class="code-keyword">public</span> void stop(BundleContext context)
705 {
706 <span class="code-comment">// Unregister the property lookup service.
707</span> m_registration.unregister();
708 m_context = <span class="code-keyword">null</span>;
709 }
710}</pre>
711</div></div>
712
713<p>Given the above host application bundle activator, the following
714code snippet shows how the host application could create an embedded
715version of the Felix framework and provide the property lookup service
716to installed bundles:</p>
717
718<div class="code"><div class="codeContent">
719<pre class="code-java"><span class="code-keyword">package</span> host.core;
720
721<span class="code-keyword">import</span> java.util.List;
722<span class="code-keyword">import</span> java.util.ArrayList;
723<span class="code-keyword">import</span> java.util.Map;
724<span class="code-keyword">import</span> java.util.HashMap;
725<span class="code-keyword">import</span> host.service.lookup.Lookup;
726<span class="code-keyword">import</span> org.apache.felix.framework.Felix;
727<span class="code-keyword">import</span> org.apache.felix.framework.util.FelixConstants;
728<span class="code-keyword">import</span> org.osgi.framework.Constants;
729
730<span class="code-keyword">public</span> class HostApplication
731{
732 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
733 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
734 <span class="code-keyword">private</span> Map m_lookupMap = <span class="code-keyword">new</span> HashMap();
735
736 <span class="code-keyword">public</span> HostApplication()
737 {
738 <span class="code-comment">// Initialize the map <span class="code-keyword">for</span> the property lookup service.
739</span> m_lookupMap.put(<span class="code-quote">"name1"</span>, <span class="code-quote">"value1"</span>);
740
741 m_lookupMap.put(<span class="code-quote">"name2"</span>, <span class="code-quote">"value2"</span>);
742 m_lookupMap.put(<span class="code-quote">"name3"</span>, <span class="code-quote">"value3"</span>);
743 m_lookupMap.put(<span class="code-quote">"name4"</span>, <span class="code-quote">"value4"</span>);
744
745 <span class="code-comment">// Create a configuration property map.
746</span> Map configMap = <span class="code-keyword">new</span> HashMap();
747 <span class="code-comment">// Export the host provided service <span class="code-keyword">interface</span> <span class="code-keyword">package</span>.
748</span> configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
749 <span class="code-quote">"host.service.lookup; version=1.0.0"</span>);
750 <span class="code-comment">// Create host activator;
751</span> m_activator = <span class="code-keyword">new</span> HostActivator(m_lookupMap);
752 List list = <span class="code-keyword">new</span> ArrayList();
753 list.add(m_activator);
754 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
755
756 <span class="code-keyword">try</span>
757 {
758 <span class="code-comment">// Now create an instance of the framework with
759</span> <span class="code-comment">// our configuration properties.
760</span> m_felix = <span class="code-keyword">new</span> Felix(configMap);
761 <span class="code-comment">// Now start Felix instance.
762</span> m_felix.start();
763 }
764 <span class="code-keyword">catch</span> (Exception ex)
765 {
766 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
767 ex.printStackTrace();
768 }
769 }
770
771 <span class="code-keyword">public</span> void shutdownApplication()
772 {
773 <span class="code-comment">// Shut down the felix framework when stopping the
774</span> <span class="code-comment">// host application.
775</span> m_felix.stop();
776 m_felix.waitForStop();
777 }
778}</pre>
779</div></div>
780
781<p>Rather than having the host application bundle activator register
782the service, it is also possible for the the host application to simply
783get the bundle context from the bundle activator and register the
784service directly, but the presented approach is perhaps a little
785cleaner since it allows the host application to register/unregister the
786service when the system bundle starts/stops.</p>
787
788<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostserviceusage"></a></p>
789
790<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-UsingServicesProvidedbyBundles"></a>Using Services Provided by Bundles</h2>
791
792<p>Using services provided by bundles follows the same general approach
793of using a host application bundle activator. The main complication for
794the host application using a service from a bundle is the fact that
795both the host application and the bundle must be using the same class
796definitions for the service interface classes. Since the host
797application cannot import classes from a bundle, this means that the
798service interface classes <b>must</b> be accessible on the class path,
799typically as part of the host application itself. The host application
800then must export the service interface package via the system bundle so
801that bundles installed into the embedded framework instance can import
802it. This is achieved using the <tt>org.osgi.framework.system.packages.extra</tt> configuration property previously presented.</p>
803
804<p>Consider the following simple command service interface for which
805bundles provide implementations, such as might be used to create an
806extensible interactive shell:</p>
807
808<div class="code"><div class="codeContent">
809<pre class="code-java"><span class="code-keyword">package</span> host.service.command;
810
811<span class="code-keyword">public</span> class Command
812{
813 <span class="code-keyword">public</span> <span class="code-object">String</span> getName();
814 <span class="code-keyword">public</span> <span class="code-object">String</span> getDescription();
815 <span class="code-keyword">public</span> <span class="code-object">boolean</span> execute(<span class="code-object">String</span> commandline);
816}</pre>
817</div></div>
818
819<p>This package is simply part of the host application, which is potentially packaged into a JAR file and started with the "<tt>java -jar</tt>"
820command. Now consider the previously introduced host application bundle
821activator below, which simply provides access to the system bundle
822context:</p>
823
824<div class="code"><div class="codeContent">
825<pre class="code-java"><span class="code-keyword">package</span> host.core;
826
827<span class="code-keyword">import</span> org.osgi.framework.BundleActivator;
828<span class="code-keyword">import</span> org.osgi.framework.BundleContext;
829
830<span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
831{
832 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
833
834 <span class="code-keyword">public</span> void start(BundleContext context)
835 {
836 m_context = context;
837 }
838
839 <span class="code-keyword">public</span> void stop(BundleContext context)
840 {
841 m_context = <span class="code-keyword">null</span>;
842 }
843
844 <span class="code-keyword">public</span> BundleContext getContext()
845 {
846 <span class="code-keyword">return</span> m_context;
847 }
848}</pre>
849</div></div>
850
851<p>With this bundle activator, the host application can use command
852services provided by bundles installed inside its embedded Felix
853framework instance. The following code snippet illustrates one possible
854approach:</p>
855
856<div class="code"><div class="codeContent">
857<pre class="code-java"><span class="code-keyword">package</span> host.core;
858
859<span class="code-keyword">import</span> java.util.List;
860<span class="code-keyword">import</span> java.util.ArrayList;
861<span class="code-keyword">import</span> java.util.Map;
862<span class="code-keyword">import</span> host.service.command.Command;
863<span class="code-keyword">import</span> org.apache.felix.framework.Felix;
864<span class="code-keyword">import</span> org.apache.felix.framework.util.FelixConstants;
865<span class="code-keyword">import</span> org.apache.felix.framework.cache.BundleCache;
866<span class="code-keyword">import</span> org.osgi.framework.Constants;
867<span class="code-keyword">import</span> org.osgi.util.tracker.ServiceTracker;
868
869<span class="code-keyword">public</span> class HostApplication
870{
871 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
872 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
873 <span class="code-keyword">private</span> ServiceTracker m_tracker = <span class="code-keyword">null</span>;
874
875 <span class="code-keyword">public</span> HostApplication()
876 {
877 <span class="code-comment">// Create a configuration property map.
878</span> Map configMap = <span class="code-keyword">new</span> HashMap();
879 <span class="code-comment">// Export the host provided service <span class="code-keyword">interface</span> <span class="code-keyword">package</span>.
880</span> configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
881 <span class="code-quote">"host.service.command; version=1.0.0"</span>);
882 <span class="code-comment">// Create host activator;
883</span> m_activator = <span class="code-keyword">new</span> HostActivator();
884 List list = <span class="code-keyword">new</span> ArrayList();
885 list.add(m_activator);
886 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
887
888 <span class="code-keyword">try</span>
889 {
890 <span class="code-comment">// Now create an instance of the framework with
891</span> <span class="code-comment">// our configuration properties.
892</span> m_felix = <span class="code-keyword">new</span> Felix(configMap);
893 <span class="code-comment">// Now start Felix instance.
894</span> m_felix.start();
895 }
896 <span class="code-keyword">catch</span> (Exception ex)
897 {
898 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
899 ex.printStackTrace();
900 }
901
902 m_tracker = <span class="code-keyword">new</span> ServiceTracker(
903 m_activator.getContext(), Command.class.getName(), <span class="code-keyword">null</span>);
904 m_tracker.open();
905 }
906
907 <span class="code-keyword">public</span> <span class="code-object">boolean</span> execute(<span class="code-object">String</span> name, <span class="code-object">String</span> commandline)
908 {
909 <span class="code-comment">// See <span class="code-keyword">if</span> any of the currently tracked command services
910</span> <span class="code-comment">// match the specified command name, <span class="code-keyword">if</span> so then execute it.
911</span> <span class="code-object">Object</span>[] services = m_tracker.getServices();
912 <span class="code-keyword">for</span> (<span class="code-object">int</span> i = 0; (services != <span class="code-keyword">null</span>) &amp;&amp; (i &lt; services.length); i++)
913 {
914 <span class="code-keyword">try</span>
915 {
916 <span class="code-keyword">if</span> (((Command) services[i]).getName().equals(name))
917 {
918 <span class="code-keyword">return</span> ((Command) services[i]).execute(commandline);
919 }
920 }
921 <span class="code-keyword">catch</span> (Exception ex)
922 {
923 <span class="code-comment">// Since the services returned by the tracker could become
924</span> <span class="code-comment">// invalid at any moment, we will <span class="code-keyword">catch</span> all exceptions, log
925</span> <span class="code-comment">// a message, and then ignore faulty services.
926</span> <span class="code-object">System</span>.err.println(ex);
927 }
928 }
929 <span class="code-keyword">return</span> <span class="code-keyword">false</span>;
930 }
931
932 <span class="code-keyword">public</span> void shutdownApplication()
933 {
934 {
935 <span class="code-comment">// Shut down the felix framework when stopping the
936</span> <span class="code-comment">// host application.
937</span> m_felix.stop();
938 m_felix.waitForStop();
939 }
940}</pre>
941</div></div>
942
943<p>The above example is overly simplistic with respect to concurrency
944issues and error conditions, but it demonstrates the overall approach
945for using bundle-provided services from the host application.</p>
946
947<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-servicereflection"></a></p>
948
949<h3><a name="ApacheFelixFrameworkLaunchingandEmbedding-UsingBundleServicesviaReflection"></a>Using Bundle Services via Reflection</h3>
950
951<p>It possible for the host application to use services provided by
952bundles without having access to the service interface classes and thus
953not needing to put the service interface classes on the class path. To
954do this, the host application uses the same general approach to acquire
955the system bundle context object, which it can use to look up service
956objects. Using either an LDAP filter or the service interface class
957name, the host application can retrieve the service object and then use
958standard Java reflection to invoke methods on the service object.</p>
959
960<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-serviceother"></a></p>
961
962<h3><a name="ApacheFelixFrameworkLaunchingandEmbedding-OtherApproaches"></a>Other Approaches</h3>
963
964<p>The <span class="nobr"><a href="http://code.google.com/p/transloader/" title="Visit page outside Confluence" rel="nofollow">Transloader<sup><img class="rendericon" src="apache-felix-framework-launching-and-embedding_files/linkext7.gif" alt="" align="absmiddle" border="0" height="7" width="7"></sup></a></span> project is another attempt at dealing with issues of classes loaded from different class loaders and may be of interest.</p>
965
966<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-caveat"></a></p>
967
968<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-Caveat"></a>Caveat</h1>
969
970<p>The code in this document has not been thoroughly tested nor even
971compiled and may be out of date with respect to the current Felix
972source code. If you find errors please report them so the that they can
973be corrected.</p>
974
975<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-feedback"></a></p>
976
977<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-Feedback"></a>Feedback</h2>
978
979<p>Subscribe to the Felix users mailing list by sending a message to <span class="nobr"><a href="mailto:users-subscribe@felix.apache.org" title="Send mail to users-subscribe@felix.apache.org" rel="nofollow">users-subscribe@felix.apache.org<sup><img class="rendericon" src="apache-felix-framework-launching-and-embedding_files/mail_small.gif" alt="" align="absmiddle" border="0" height="12" width="13"></sup></a></span>; after subscribing, email questions or feedback to <span class="nobr"><a href="mailto:users@felix.apache.org" title="Send mail to users@felix.apache.org" rel="nofollow">users@felix.apache.org<sup><img class="rendericon" src="apache-felix-framework-launching-and-embedding-Dateien/mail_small.gif" alt="" align="absmiddle" border="0" height="12" width="13"></sup></a></span>.</p>
980 </div>
981 </body></html>