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Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]29 <div class="main">
30<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-ApacheFelixFrameworkLaunchingandEmbedding"></a>Apache Felix Framework Launching and Embedding</h1>
31
32<p><em>[This document describes framework launching introduced in Felix
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]33Framework 2.0.0 and continuing with the latest releases; it is
34incompatible with older versions of the Felix framework.]</em></p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]35
36<ul>
37 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-introduction">Introduction</a></li>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]38 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-overview">OSGi Launching and Embedding API Overview</a>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]39 <ul>
40 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-creatingandconfiguring">Creating and Configuring the Framework Instance</a></li>
41 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-startinginstance">Starting the Framework Instance</a></li>
42 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-stoppinginstance">Stopping the Framework Instance</a></li>
43 </ul>
44 </li>
45 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-launching">Launching Felix</a>
46 <ul>
47 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-standardlauncher">Standard Felix Launcher</a></li>
48 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-customlauncher">Custom Felix Launcher</a></li>
49 </ul>
50 </li>
51 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-embedding">Embedding Felix</a>
52 <ul>
53 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction">Host/Felix Interaction</a></li>
54 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostservices">Providing Host Application Services</a></li>
55 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostserviceusage">Using Services Provided by Bundles</a>
56 <ul>
57 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-servicereflection">Using Bundle Services via Reflection</a></li>
58 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-serviceother">Other Approaches</a></li>
59 </ul>
60 </li>
61 </ul>
62 </li>
63 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-caveat">Caveat</a></li>
64 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-feedback">Feedback</a></li>
65</ul>
66
67
68<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-introduction"></a></p>
69
70<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-Introduction"></a>Introduction</h1>
71
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]72<p>The Apache Felix Framework is intended to be easily launchable and
73embeddable. For example, the Felix framework implementation avoids the
74use of system properties for configuration, since these are globals and
75can cause interference if multiple framework instances are created in
76the same VM. The framework also tries to multiplex singleton
77facilities, like the URL stream handler factory. The goal is to make it
78possible to use the framework in a variety of scenarios; however, this
79is still just a goal. In other words, this is a work in progress and if
80any issues arise, it would be greatly appreciated if they are brought
81to the attention of the Felix community. The next section provides an
82overview of the standard OSGi launching and embedding API for
83frameworks, while the remainder of the document is divided into two
84sections, one focusing on how to launch Felix and one focusing on how
85to embed Felix into a host application.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]86
87<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-overview"></a></p>
88
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]89<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-OSGiLaunchingandEmbeddingAPIOverview"></a>OSGi Launching and Embedding API Overview</h1>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]90
91<p>The Felix framework is implemented by the <tt>org.apache.felix.framework.Felix</tt> class or just <tt>Felix</tt>
92for short. As part of the R4.2 OSGi specification, the launching and
93embedding API of the OSGi framework has been standardized. The approach
94is to have the framework implement 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>
95
96<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
97<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> Bundle
98{
99 BundleContext getBundleContext();
100 <span class="code-object">long</span> getBundleId();
101 URL getEntry(<span class="code-object">String</span> name);
102 Enumeration getEntryPaths(<span class="code-object">String</span> path);
103 Enumeration findEntries(<span class="code-object">String</span> path, <span class="code-object">String</span> filePattern, <span class="code-object">boolean</span> recurse);
104 Dictionary getHeaders();
105 Dictionary getHeaders(<span class="code-object">String</span> locale);
106 <span class="code-object">long</span> getLastModified();
107 <span class="code-object">String</span> getLocation();
108 URL getResource(<span class="code-object">String</span> name);
109 Enumeration getResources(<span class="code-object">String</span> name) <span class="code-keyword">throws</span> IOException;
110 ServiceReference[] getRegisteredServices();
111 ServiceReference[] getServicesInUse();
112 <span class="code-object">int</span> getState();
113 <span class="code-object">String</span> getSymbolicName();
114 Version getVersion();
115 <span class="code-object">boolean</span> hasPermission(<span class="code-object">Object</span> obj);
116 <span class="code-object">Class</span> loadClass(<span class="code-object">String</span> name) <span class="code-keyword">throws</span> ClassNotFoundException;
117 void start() <span class="code-keyword">throws</span> BundleException;
118 void stop() <span class="code-keyword">throws</span> BundleException;
119 void uninstall() <span class="code-keyword">throws</span> BundleException;
120 void update() <span class="code-keyword">throws</span> BundleException;
121 void update(InputStream is) <span class="code-keyword">throws</span> BundleException;
122}
123</pre>
124</div></div>
125
126<p>The <tt>Framework</tt> interface is defined as:</p>
127
128<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
129<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> Framework <span class="code-keyword">extends</span> Bundle
130{
131 void init();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]132 FrameworkEvent waitForStop(<span class="code-object">long</span> timeout);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]133}
134</pre>
135</div></div>
136
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]137<p>To actually construct a framework instance, the R4.2 specification defines the <tt>FrameworkFactory</tt> interface:</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]138
139<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
140<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> FrameworkFactory
141{
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]142 Framework newFramework(Map config);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]143}
144</pre>
145</div></div>
146
147<p>The framework factory can be used to create configured framework instances. It is obtained following the standard <tt>META-INF/services</tt> approach.</p>
148
149<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-creatingandconfiguring"></a></p>
150
151<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-CreatingandConfiguringtheFrameworkInstance"></a>Creating and Configuring the Framework Instance</h2>
152
153<p>You use the framework factory to construct and configure a framework
154instance (or by directly instantiating the Felix class). The
Karl Pauls424d5a62010-12-26 21:11:45 +0000[diff] [blame^]155configuration map may contain any of the framework configuration
156properties listed in the <a href="http://felix.apache.org/site/apache-felix-framework-configuration-properties.html" title="Apache Felix Framework Configuration Properties">Apache Felix Framework Configuration Properties</a>
157document, not the launcher configuration properties. The configuration
158map is copied and the keys are treated as case insensitive. You are not
159able to change the framework's configuration after construction. If you
160need a different configuration, you must create a new framework
161instance.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]162
Karl Pauls424d5a62010-12-26 21:11:45 +0000[diff] [blame^]163<div class="panelMacro"><table class="warningMacro"><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>WARNING</b><br>Felix configuration properties have change considerably starting from <tt>1.4.0</tt>; if you are upgrading from an earlier version, the <a href="http://felix.apache.org/site/apache-felix-framework-configuration-properties.html#ApacheFelixFrameworkConfigurationProperties-migrating">configuration property document</a> describes the configuration property changes.</td></tr></tbody></table></div>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]164
165<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-startinginstance"></a></p>
166
167<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StartingtheFrameworkInstance"></a>Starting the Framework Instance</h2>
168
169<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 invoked by <tt>start()</tt>. The two methods result in two different framework state transitions:</p>
170
171<ul>
172 <li><tt>init()</tt> results in the framework instance in the <tt>Bundle.STARTING</tt> state.</li>
173 <li><tt>start()</tt> results in the framework instance in the <tt>Bundle.ACTIVE</tt> state.</li>
174</ul>
175
176
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]177<p>The <tt>init()</tt> method is necessary since the framework does not have a <tt>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 the Felix framework also provides the <tt>felix.systembundle.activators</tt> property that serves a similar purpose, but is not standard. After the <tt>init()</tt> method completes, the follow actions have been performed:</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]178
179<ul>
180 <li>Event handling is enabled.</li>
181 <li>The security manager is installed if it is enabled.</li>
182 <li>The framework is set to start level 0.</li>
183 <li>All bundles in the bundle caches are reified and their state is set to <tt>Bundle.INSTALLED</tt>.</li>
184 <li>The framework gets a valid <tt>BundleContext</tt>.</li>
185 <li>All framework-provided services are made available (e.g., PackageAdmin, StartLevel, etc.).</li>
186 <li>The framework enters the <tt>Bundle.STARTING</tt> state.</li>
187</ul>
188
189
190<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>
191
192<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-stoppinginstance"></a></p>
193
194<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StoppingtheFrameworkInstance"></a>Stopping the Framework Instance</h2>
195
196<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>
197
198<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-launching"></a></p>
199
200<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-LaunchingaFramework"></a>Launching a Framework</h1>
201
202<p>Launching a framework is fairly simple and involves only four steps:</p>
203
204<ol>
205 <li>Define some configuration properties.</li>
206 <li>Obtain framework factory.</li>
207 <li>Use factory to create framework with the configuration properties.</li>
208 <li>Invoke the <tt>Framework.start()</tt> method.</li>
209</ol>
210
211
212<p>In reality, the first step is optional, since all properties will
213have reasonable defaults, but if you are creating a launcher you will
214generally want to more than that, such as automatically installing and
215starting bundles when you start the framework instance. The default
216Felix launcher defines reusable functionality to automatically install
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]217and/or start bundles upon framework startup; see the <a href="http://felix.apache.org/site/apache-felix-framework-usage-documentation.html#ApacheFelixFrameworkUsageDocumentation-configuringfelix">usage document</a> for more information on configuring the Felix framework and on the various configuration properties.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]218
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]219<p>The remainder of this section describes how the standard Felix launcher works as well as how to create a custom launcher.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]220
221<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-standardlauncher"></a></p>
222
223<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StandardFelixFrameworkLauncher"></a>Standard Felix Framework Launcher</h2>
224
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]225<p>The standard Felix framework launcher is very simple and is not
226intended to solve every possible requirement; it is intended to work
227for most standard situations. Most special launching requirements
228should be resolved by creating a custom launcher. This section
229describes how the standard launcher works. The following code
230represents the complete <tt>main()</tt> method of the standard launcher, each numbered comment will be described in more detail below:</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]231
232<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
233<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">static</span> void main(<span class="code-object">String</span>[] args) <span class="code-keyword">throws</span> Exception
234{
235 <span class="code-comment">// (1) Check <span class="code-keyword">for</span> command line arguments and verify usage.
236</span> <span class="code-object">String</span> bundleDir = <span class="code-keyword">null</span>;
237 <span class="code-object">String</span> cacheDir = <span class="code-keyword">null</span>;
238 <span class="code-object">boolean</span> expectBundleDir = <span class="code-keyword">false</span>;
239 <span class="code-keyword">for</span> (<span class="code-object">int</span> i = 0; i &lt; args.length; i++)
240 {
241 <span class="code-keyword">if</span> (args[i].equals(BUNDLE_DIR_SWITCH))
242 {
243 expectBundleDir = <span class="code-keyword">true</span>;
244 }
245 <span class="code-keyword">else</span> <span class="code-keyword">if</span> (expectBundleDir)
246 {
247 bundleDir = args[i];
248 expectBundleDir = <span class="code-keyword">false</span>;
249 }
250 <span class="code-keyword">else</span>
251 {
252 cacheDir = args[i];
253 }
254 }
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]255
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]256 <span class="code-keyword">if</span> ((args.length &gt; 3) || (expectBundleDir &amp;&amp; bundleDir == <span class="code-keyword">null</span>))
257 {
258 <span class="code-object">System</span>.out.println(<span class="code-quote">"Usage: [-b &lt;bundle-deploy-dir&gt;] [&lt;bundle-cache-dir&gt;]"</span>);
259 <span class="code-object">System</span>.exit(0);
260 }
261
262 <span class="code-comment">// (2) Load system properties.
263</span> Main.loadSystemProperties();
264
265 <span class="code-comment">// (3) Read configuration properties.
266</span> Properties configProps = Main.loadConfigProperties();
267 <span class="code-keyword">if</span> (configProps == <span class="code-keyword">null</span>)
268 {
269 <span class="code-object">System</span>.err.println(<span class="code-quote">"No "</span> + CONFIG_PROPERTIES_FILE_VALUE + <span class="code-quote">" found."</span>);
270 configProps = <span class="code-keyword">new</span> Properties();
271 }
272
273 <span class="code-comment">// (4) Copy framework properties from the system properties.
274</span> Main.copySystemProperties(configProps);
275
276 <span class="code-comment">// (5) Use the specified auto-deploy directory over <span class="code-keyword">default</span>.
277</span> <span class="code-keyword">if</span> (bundleDir != <span class="code-keyword">null</span>)
278 {
279 configProps.setProperty(AutoProcessor.AUTO_DEPLOY_DIR_PROPERY, bundleDir);
280 }
281
282 <span class="code-comment">// (6) Use the specified bundle cache directory over <span class="code-keyword">default</span>.
283</span> <span class="code-keyword">if</span> (cacheDir != <span class="code-keyword">null</span>)
284 {
285 configProps.setProperty(Constants.FRAMEWORK_STORAGE, cacheDir);
286 }
287
288 <span class="code-comment">// (7) Add a shutdown hook to clean stop the framework.
289</span> <span class="code-object">String</span> enableHook = configProps.getProperty(SHUTDOWN_HOOK_PROP);
290 <span class="code-keyword">if</span> ((enableHook == <span class="code-keyword">null</span>) || !enableHook.equalsIgnoreCase(<span class="code-quote">"<span class="code-keyword">false</span>"</span>))
291 {
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]292 <span class="code-object">Runtime</span>.getRuntime().addShutdownHook(<span class="code-keyword">new</span> <span class="code-object">Thread</span>(<span class="code-quote">"Felix Shutdown Hook"</span>) {
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]293 <span class="code-keyword">public</span> void run()
294 {
295 <span class="code-keyword">try</span>
296 {
297 <span class="code-keyword">if</span> (m_fwk != <span class="code-keyword">null</span>)
298 {
299 m_fwk.stop();
300 m_fwk.waitForStop(0);
301 }
302 }
303 <span class="code-keyword">catch</span> (Exception ex)
304 {
305 <span class="code-object">System</span>.err.println(<span class="code-quote">"Error stopping framework: "</span> + ex);
306 }
307 }
308 });
309 }
310
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]311 <span class="code-keyword">try</span>
312 {
313 <span class="code-comment">// (8) Create an instance and initialize the framework.
314</span> FrameworkFactory factory = getFrameworkFactory();
315 m_fwk = factory.newFramework(configProps);
316 m_fwk.init();
317 <span class="code-comment">// (9) Use the system bundle context to process the auto-deploy
318</span> <span class="code-comment">// and auto-install/auto-start properties.
319</span> AutoProcessor.process(configProps, m_fwk.getBundleContext());
320 <span class="code-comment">// (10) Start the framework.
321</span> m_fwk.start();
322 <span class="code-comment">// (11) Wait <span class="code-keyword">for</span> framework to stop to exit the VM.
323</span> m_fwk.waitForStop(0);
324 <span class="code-object">System</span>.exit(0);
325 }
326 <span class="code-keyword">catch</span> (Exception ex)
327 {
328 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
329 ex.printStackTrace();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]330 <span class="code-object">System</span>.exit(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]331 }
332}
333</pre>
334</div></div>
335
336<p>The general steps of the standard launcher are quite straightforward:</p>
337
338<ol>
339 <li>The launcher supports setting the auto-deploy directory (with the <tt>-b</tt>
340switch) and setting the bundle cache path with a single argument, so
341check for this and issue a usage message it there are more than one
342arguments.</li>
343 <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>
344system property. This file is not needed to launch Felix and is
345provided merely for convenience when system properties must be
346specified. The file is a standard Java properties file, but it also
347supports property substitution using <tt>${&lt;property-name</tt>} syntax. Property substitution can be nested; only system properties will be used for substitution.</li>
348 <li>Load any configuration properties specified in the <tt>config.properties</tt> file; this file is typically located in the <tt>conf/</tt> directory of the Felix installation directory, but it can be specified directly using the <tt>felix.config.properties</tt>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]349system property. This file is used to configure the framework instance
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]350created by the launcher. The file is a standard Java properties file,
351but it also supports property substitution using "<tt>${&lt;property-name&gt;</tt>}"
352syntax. Property substitution can be nested; configuration and system
353properties will be used for substitution with configuration properties
354having precedence.</li>
355 <li>For convenience, any configuration
356properties that are set as system properties are copied into the set of
357configuration properties. This provide an easy way to add to or
358override configuration properties specified in the <tt>config.properties</tt> file, since the Felix instance will never look at system properties for configuration.</li>
359 <li>If the <tt>-b</tt> switch was used to specify an auto-deploy directory, then use that to set the value of <tt>felix.auto.deploy.dir</tt>.</li>
360 <li>If a single command-line argument is specified, 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>
361 <li>Add a shutdown hook to cleanly stop the framework, unless the hook is disabled.</li>
362 <li>Create a framework instance using the <tt>FrameworkFactory</tt> passing in the configuration properties, then initialize the factory instance; see the <a href="#ApacheFelixFrameworkLaunchingandEmbedding-customlauncher">custom launcher example</a> below to see how the META-INF/services <tt>FrameworkFactory</tt> is obtained.</li>
363 <li>Use <tt>org.apache.felix.main.AutoProcessor</tt>, which will automatically deploy any bundles in the auto-deploy directory as well as bundles specified in the <tt>felix.auto.install</tt> and <tt>felix.auto.start</tt>
364configuration properties during framework startup to automatically
365install and/or start bundles; see the usage document for more
366information <a href="http://felix.apache.org/site/apache-felix-framework-usage-documentation.html#ApacheFelixFrameworkUsageDocumentation-configuringframework">configuration properties</a> and <a href="http://felix.apache.org/site/apache-felix-framework-usage-documentation.html#ApacheFelixFrameworkUsageDocumentation-autodeploy">bundle auto-deploy</a>.</li>
367 <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>
368</ol>
369
370
371<p>The framework is not active until the <tt>start()</tt> method is
372called. If no shell bundles are installed and started or if there is
373difficulty locating the shell bundles specified in the auto-start
374property, then it will appear as if the framework is hung, but it is
375actually running without any way to interact with it since the shell
376bundles provide the only means of interaction.</p>
377
378<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-customlauncher"></a></p>
379
380<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-CustomFrameworkLauncher"></a>Custom Framework Launcher</h2>
381
382<p>This section creates a bare-bones launcher to demonstrate the
383minimum requirements for creating an interactive launcher for the Felix
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]384framework. This example uses the standard Gogo shell bundles for
385interactivity, but any other bundles could be used instead. This
386example launcher project has the following directory structure:</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]387
388<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
389<pre>launcher/
390 lib/
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]391 org.apache.felix.main-3.0.0.jar
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]392 bundle/
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]393 org.apache.felix.gogo.command-0.6.0.jar
394 org.apache.felix.gogo.runtime-0.6.0.jar
395 org.apache.felix.gogo.shell-0.6.0.jar
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]396 src/
397 example/
398 Main.java
399</pre>
400</div></div>
401
402<p>The <tt>lib/</tt> directory contains Felix' main JAR file, which
403also contains the OSGi core interfaces. The main JAR file is used so
404that we can reuse the default launcher's auto-install/auto-start
405configuration property handling; if these capabilities are not needed,
406then it would be possible to use the framework JAR file instead of the
407main JAR file. The <tt>bundle/</tt> directory contains the shell
408service and textual shell interface bundles that will be used for
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]409interacting with the framework instance. Note: If you do not launch the
410framework with interactive bundles, it will appear as if the framework
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]411instance is hung, but it is actually just sitting there waiting for
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]412someone 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 framework launcher.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]413
414<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
415<pre class="code-java"><span class="code-keyword">package</span> example;
416
417<span class="code-keyword">import</span> java.io.*;
418<span class="code-keyword">import</span> org.osgi.framework.launch.*;
419<span class="code-keyword">import</span> org.apache.felix.main.AutoProcessor;
420
421<span class="code-keyword">public</span> class Main
422{
423 <span class="code-keyword">private</span> <span class="code-keyword">static</span> Framework m_fwk = <span class="code-keyword">null</span>;
424
425 <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
426 {
427 <span class="code-comment">// Print welcome banner.
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]428</span> <span class="code-object">System</span>.out.println(<span class="code-quote">"\nWelcome to My Launcher"</span>);
429 <span class="code-object">System</span>.out.println(<span class="code-quote">"======================\n"</span>);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]430
431 <span class="code-keyword">try</span>
432 {
433 m_fwk = getFrameworkFactory().newFramework(<span class="code-keyword">null</span>);
434 m_fwk.init()
435 AutoProcessor.process(<span class="code-keyword">null</span>, m_fwk.getBundleContext());
436 m_fwk.start();
Karl Pauls424d5a62010-12-26 21:11:45 +0000[diff] [blame^]437 m_fwk.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]438 <span class="code-object">System</span>.exit(0);
439 }
440 <span class="code-keyword">catch</span> (Exception ex)
441 {
442 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
443 ex.printStackTrace();
444 <span class="code-object">System</span>.exit(-1);
445 }
446 }
447
448 <span class="code-keyword">private</span> <span class="code-keyword">static</span> FrameworkFactory getFrameworkFactory() <span class="code-keyword">throws</span> Exception
449 {
450 URL url = Main.class.getClassLoader().getResource(
451 <span class="code-quote">"META-INF/services/org.osgi.framework.launch.FrameworkFactory"</span>);
452 <span class="code-keyword">if</span> (url != <span class="code-keyword">null</span>)
453 {
454 BufferedReader br = <span class="code-keyword">new</span> BufferedReader(<span class="code-keyword">new</span> InputStreamReader(url.openStream()));
455 <span class="code-keyword">try</span>
456 {
457 <span class="code-keyword">for</span> (<span class="code-object">String</span> s = br.readLine(); s != <span class="code-keyword">null</span>; s = br.readLine())
458 {
459 s = s.trim();
460 <span class="code-comment">// Try to load first non-empty, non-commented line.
461</span> <span class="code-keyword">if</span> ((s.length() &gt; 0) &amp;&amp; (s.charAt(0) != '#'))
462 {
463 <span class="code-keyword">return</span> (FrameworkFactory) <span class="code-object">Class</span>.forName(s).newInstance();
464 }
465 }
466 }
467 <span class="code-keyword">finally</span>
468 {
469 <span class="code-keyword">if</span> (br != <span class="code-keyword">null</span>) br.close();
470 }
471 }
472
473 <span class="code-keyword">throw</span> <span class="code-keyword">new</span> Exception(<span class="code-quote">"Could not find framework factory."</span>);
474 }
475}
476</pre>
477</div></div>
478
479<p>This launcher relies on the default behavior of <tt>AutoProcessor</tt>
480to automatically deploy the shell bundles. This simple, generic
481launcher provides a good starting point if the default Felix launcher
482is not sufficient. Since very few configuration properties are
483specified, the default values are used. For the bundle auto-deploy
484directory, "<tt>bundle</tt>" in the current directory is used, while for the framework bundle cache, "<tt>felix-cache</tt>" in the current directory is used.</p>
485
486<p>By breaking down the above source code into small chunks, it is quite easy to see what is going on.</p>
487
488<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
489<pre class="code-java"> m_fwk = getFrameworkFactory().newFramework(<span class="code-keyword">null</span>);
490 m_fwk.init()
491</pre>
492</div></div>
493
494<p>These steps get a the framework factory service and use it to create
495a framework instance with a default configuration. Once the framework
496instance is created, it is initialized with <tt>init()</tt>.</p>
497
498<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
499<pre class="code-java"> AutoProcessor.process(<span class="code-keyword">null</span>, m_fwk.getBundleContext());
500</pre>
501</div></div>
502
503<p>The <tt>AutorProcessor</tt> will automatically deploy bundles in the
504auto-deploy directory and any referenced from the auto-install/start
505properties. Since we are using an empty configuration, the auto-deploy
506directory is the <tt>bundle</tt> directory in the current directory
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]507and there are no auto properties. Therefore, in this case, the shell
508bundles will be installed.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]509
510<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
511<pre class="code-java"> m_fwk.start();
Karl Pauls424d5a62010-12-26 21:11:45 +0000[diff] [blame^]512 m_fwk.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]513 <span class="code-object">System</span>.exit(0);
514</pre>
515</div></div>
516
517<p>These final steps start the framework and cause the launching
518application thread to wait for the framework to stop and when it does
519the launching thread calls <tt>System.exit()</tt> to make sure the VM actually exits.</p>
520
521<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
522<pre class="code-java"> <span class="code-keyword">private</span> <span class="code-keyword">static</span> FrameworkFactory getFrameworkFactory() <span class="code-keyword">throws</span> Exception
523 {
524 ...
525 }
526</pre>
527</div></div>
528
529<p>This method retrieves the framework factory service by doing a
530META-INF/services resource lookup, which it can use to obtain the
531concrete class name for the factory. If you are using Java 6, then you
532can use the <tt>ServiceLoader</tt> API in the JRE to further simplify the factory service lookup.</p>
533
534<p>The following command compiles the launcher when run from the root directory of the launcher project:</p>
535
536<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]537<pre>javac -d . -classpath lib/org.apache.felix.main-3.0.0.jar src/example/Main.java
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]538</pre>
539</div></div>
540
541<p>After executing this command, an <tt>example/</tt> directory is
542created in the current directory, which contains the generated class
543file. The following command executes the simple launcher when run from
544the root directory of the launcher project:</p>
545
546<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]547<pre>java -cp .:lib/org.apache.felix.main-3.0.0.jar example.Main
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]548</pre>
549</div></div>
550
551<p>After executing this command, a "<tt>felix-cache/</tt>" directory is created that contains the cached bundles, which were installed from the <tt>bundle/</tt> directory.</p>
552
553<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-embedding"></a></p>
554
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]555<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-EmbeddingtheFelixFramework"></a>Embedding the Felix Framework</h1>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]556
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]557<p>Embedding the Felix framework into a host application is a simple
558way to provide a sophisticated extensibility mechanism (i.e., a plugin
559system) to the host application. Embedding the Felix framework is very
560similar to launching it as described above, the main difference is that
561the host application typically wants to interact with the framework
562instance and/or installed bundles/services from the outside. This is
563fairly easy to achieve, but there are some subtle issues to understand.
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]564This section presents the mechanisms for embedding Felix into a host
565application and the issues in doing so.</p>
566
567<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction"></a></p>
568
569<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-Host/FelixInteraction"></a>Host/Felix Interaction</h2>
570
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]571<p>In the section on <a href="#ApacheFelixFrameworkLaunchingandEmbedding-launching">launching</a> the framework above, the <tt>Felix</tt> class accepts a configuration property called <tt>felix.systembundle.activators</tt>,
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]572which is a list of bundle activator instances. These bundle activator
573instances provide a convenient way for host applications to interact
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]574with the Felix framework.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]575
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]576<div class="panelMacro"><table class="warningMacro"><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>WARNING</b><br>The <tt>felix.systembundle.activators</tt>
577configuration property is specific to the Felix framework
578implementation. If you want your code to work with other framework
579implementations, you should call <tt>init()</tt> on the framework instance and use <tt>getBundleContext()</tt> directly. Otherwise, the approach would be very similar.</td></tr></tbody></table></div>
580
581<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>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]582
583<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
584<pre class="code-java"><span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
585{
586 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
587
588 <span class="code-keyword">public</span> void start(BundleContext context)
589 {
590 m_context = context;
591 }
592
593 <span class="code-keyword">public</span> void stop(BundleContext context)
594 {
595 m_context = <span class="code-keyword">null</span>;
596 }
597
598 <span class="code-keyword">public</span> Bundle[] getBundles()
599 {
600 <span class="code-keyword">if</span> (m_context != <span class="code-keyword">null</span>)
601 {
602 <span class="code-keyword">return</span> m_context.getBundles();
603 }
604 <span class="code-keyword">return</span> <span class="code-keyword">null</span>;
605 }
606}
607</pre>
608</div></div>
609
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]610<p>Given the above bundle activator, it is now possible to embed the
611Felix framework into a host application and interact with it as the
612following snippet illustrates:</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]613
614<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
615<pre class="code-java"><span class="code-keyword">public</span> class HostApplication
616{
617 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
618 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
619
620 <span class="code-keyword">public</span> HostApplication()
621 {
622 <span class="code-comment">// Create a configuration property map.
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]623</span> Map config = <span class="code-keyword">new</span> HashMap();
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]624 <span class="code-comment">// Create host activator;
625</span> m_activator = <span class="code-keyword">new</span> HostActivator();
626 List list = <span class="code-keyword">new</span> ArrayList();
627 list.add(m_activator);
628 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
629
630 <span class="code-keyword">try</span>
631 {
632 <span class="code-comment">// Now create an instance of the framework with
633</span> <span class="code-comment">// our configuration properties.
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]634</span> m_felix = <span class="code-keyword">new</span> Felix(config);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]635 <span class="code-comment">// Now start Felix instance.
636</span> m_felix.start();
637 }
638 <span class="code-keyword">catch</span> (Exception ex)
639 {
640 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
641 ex.printStackTrace();
642 }
643 }
644
645 <span class="code-keyword">public</span> Bundle[] getInstalledBundles()
646 {
647 <span class="code-comment">// Use the system bundle activator to gain external
648</span> <span class="code-comment">// access to the set of installed bundles.
649</span> <span class="code-keyword">return</span> m_activator.getBundles();
650 }
651
652 <span class="code-keyword">public</span> void shutdownApplication()
653 {
654 <span class="code-comment">// Shut down the felix framework when stopping the
655</span> <span class="code-comment">// host application.
656</span> m_felix.stop();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]657 m_felix.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]658 }
659}
660</pre>
661</div></div>
662
663<p>Notice how the <tt>HostApplication.getInstalledBundles()</tt> method
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]664uses its activator instance to get access to the system bundle's
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]665context in order to interact with the embedded Felix framework
666instance. This approach provides the foundation for all interaction
667between the host application and the embedded framework instance.</p>
668
669<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostservices"></a></p>
670
671<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-ProvidingHostApplicationServices"></a>Providing Host Application Services</h2>
672
673<p>Providing services from the host application to bundles inside the
674embedded Felix framework instance follows the basic approach laid out
675in <a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction">above</a>.
676The main complication for providing a host application service to
677bundles is the fact that both the host application and the bundles must
678be using the same class definitions for the service interface classes.
679Since the host application cannot import classes from a bundle, this
680means that the service interface classes <b>must</b> be accessible on
681the class path, typically as part of the host application itself. The
682host application then must export the service interface package via the
683system bundle so that bundles installed into the embedded framework
684instance can import it. This is achieved using the <tt>org.osgi.framework.system.packages.extra</tt> configuration property previously presented.</p>
685
686<p>Consider the follow simple property lookup service:</p>
687
688<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
689<pre class="code-java"><span class="code-keyword">package</span> host.service.lookup;
690
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]691<span class="code-keyword">public</span> <span class="code-keyword">interface</span> Lookup
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]692{
693 <span class="code-keyword">public</span> <span class="code-object">Object</span> lookup(<span class="code-object">String</span> name);
694}
695</pre>
696</div></div>
697
698<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>"
699command. Now consider the following host application bundle activator,
700which will be used to register/unregister the property lookup service
701when the embedded framework instance starts/stops:</p>
702
703<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
704<pre class="code-java"><span class="code-keyword">package</span> host.core;
705
706<span class="code-keyword">import</span> java.util.Map;
707<span class="code-keyword">import</span> org.osgi.framework.BundleActivator;
708<span class="code-keyword">import</span> org.osgi.framework.BundleContext;
709<span class="code-keyword">import</span> org.osgi.framework.ServiceRegistration;
710<span class="code-keyword">import</span> host.service.lookup;
711
712<span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
713{
714 <span class="code-keyword">private</span> Map m_lookupMap = <span class="code-keyword">null</span>;
715 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
716 <span class="code-keyword">private</span> ServiceRegistration m_registration = <span class="code-keyword">null</span>;
717
718 <span class="code-keyword">public</span> HostActivator(Map lookupMap)
719 {
720 <span class="code-comment">// Save a reference to the service's backing store.
721</span> m_lookupMap = lookupMap;
722 }
723
724 <span class="code-keyword">public</span> void start(BundleContext context)
725 {
726 <span class="code-comment">// Save a reference to the bundle context.
727</span> m_context = context;
728 <span class="code-comment">// Create a property lookup service implementation.
729</span> Lookup lookup = <span class="code-keyword">new</span> Lookup() {
730 <span class="code-keyword">public</span> <span class="code-object">Object</span> lookup(<span class="code-object">String</span> name)
731 {
732 <span class="code-keyword">return</span> m_lookupMap.get(name);
733 }
734 };
735 <span class="code-comment">// Register the property lookup service and save
736</span> <span class="code-comment">// the service registration.
737</span> m_registration = m_context.registerService(
738 Lookup.class.getName(), lookup, <span class="code-keyword">null</span>);
739 }
740
741 <span class="code-keyword">public</span> void stop(BundleContext context)
742 {
743 <span class="code-comment">// Unregister the property lookup service.
744</span> m_registration.unregister();
745 m_context = <span class="code-keyword">null</span>;
746 }
747}
748</pre>
749</div></div>
750
751<p>Given the above host application bundle activator, the following
752code snippet shows how the host application could create an embedded
753version of the Felix framework and provide the property lookup service
754to installed bundles:</p>
755
756<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
757<pre class="code-java"><span class="code-keyword">package</span> host.core;
758
759<span class="code-keyword">import</span> java.util.List;
760<span class="code-keyword">import</span> java.util.ArrayList;
761<span class="code-keyword">import</span> java.util.Map;
762<span class="code-keyword">import</span> java.util.HashMap;
763<span class="code-keyword">import</span> host.service.lookup.Lookup;
764<span class="code-keyword">import</span> org.apache.felix.framework.Felix;
765<span class="code-keyword">import</span> org.apache.felix.framework.util.FelixConstants;
766<span class="code-keyword">import</span> org.osgi.framework.Constants;
767
768<span class="code-keyword">public</span> class HostApplication
769{
770 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
771 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
772 <span class="code-keyword">private</span> Map m_lookupMap = <span class="code-keyword">new</span> HashMap();
773
774 <span class="code-keyword">public</span> HostApplication()
775 {
776 <span class="code-comment">// Initialize the map <span class="code-keyword">for</span> the property lookup service.
777</span> m_lookupMap.put(<span class="code-quote">"name1"</span>, <span class="code-quote">"value1"</span>);
778
779 m_lookupMap.put(<span class="code-quote">"name2"</span>, <span class="code-quote">"value2"</span>);
780 m_lookupMap.put(<span class="code-quote">"name3"</span>, <span class="code-quote">"value3"</span>);
781 m_lookupMap.put(<span class="code-quote">"name4"</span>, <span class="code-quote">"value4"</span>);
782
783 <span class="code-comment">// Create a configuration property map.
784</span> Map configMap = <span class="code-keyword">new</span> HashMap();
785 <span class="code-comment">// Export the host provided service <span class="code-keyword">interface</span> <span class="code-keyword">package</span>.
786</span> configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
787 <span class="code-quote">"host.service.lookup; version=1.0.0"</span>);
788 <span class="code-comment">// Create host activator;
789</span> m_activator = <span class="code-keyword">new</span> HostActivator(m_lookupMap);
790 List list = <span class="code-keyword">new</span> ArrayList();
791 list.add(m_activator);
792 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
793
794 <span class="code-keyword">try</span>
795 {
796 <span class="code-comment">// Now create an instance of the framework with
797</span> <span class="code-comment">// our configuration properties.
798</span> m_felix = <span class="code-keyword">new</span> Felix(configMap);
799 <span class="code-comment">// Now start Felix instance.
800</span> m_felix.start();
801 }
802 <span class="code-keyword">catch</span> (Exception ex)
803 {
804 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
805 ex.printStackTrace();
806 }
807 }
808
809 <span class="code-keyword">public</span> void shutdownApplication()
810 {
811 <span class="code-comment">// Shut down the felix framework when stopping the
812</span> <span class="code-comment">// host application.
813</span> m_felix.stop();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]814 m_felix.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]815 }
816}
817</pre>
818</div></div>
819
820<p>Rather than having the host application bundle activator register
821the service, it is also possible for the the host application to simply
822get the bundle context from the bundle activator and register the
823service directly, but the presented approach is perhaps a little
824cleaner since it allows the host application to register/unregister the
825service when the system bundle starts/stops.</p>
826
827<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostserviceusage"></a></p>
828
829<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-UsingServicesProvidedbyBundles"></a>Using Services Provided by Bundles</h2>
830
831<p>Using services provided by bundles follows the same general approach
832of using a host application bundle activator. The main complication for
833the host application using a service from a bundle is the fact that
834both the host application and the bundle must be using the same class
835definitions for the service interface classes. Since the host
836application cannot import classes from a bundle, this means that the
837service interface classes <b>must</b> be accessible on the class path,
838typically as part of the host application itself. The host application
839then must export the service interface package via the system bundle so
840that bundles installed into the embedded framework instance can import
841it. This is achieved using the <tt>org.osgi.framework.system.packages.extra</tt> configuration property previously presented.</p>
842
843<p>Consider the following simple command service interface for which
844bundles provide implementations, such as might be used to create an
845extensible interactive shell:</p>
846
847<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
848<pre class="code-java"><span class="code-keyword">package</span> host.service.command;
849
850<span class="code-keyword">public</span> class Command
851{
852 <span class="code-keyword">public</span> <span class="code-object">String</span> getName();
853 <span class="code-keyword">public</span> <span class="code-object">String</span> getDescription();
854 <span class="code-keyword">public</span> <span class="code-object">boolean</span> execute(<span class="code-object">String</span> commandline);
855}
856</pre>
857</div></div>
858
859<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>"
860command. Now consider the previously introduced host application bundle
861activator below, which simply provides access to the system bundle
862context:</p>
863
864<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
865<pre class="code-java"><span class="code-keyword">package</span> host.core;
866
867<span class="code-keyword">import</span> org.osgi.framework.BundleActivator;
868<span class="code-keyword">import</span> org.osgi.framework.BundleContext;
869
870<span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
871{
872 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
873
874 <span class="code-keyword">public</span> void start(BundleContext context)
875 {
876 m_context = context;
877 }
878
879 <span class="code-keyword">public</span> void stop(BundleContext context)
880 {
881 m_context = <span class="code-keyword">null</span>;
882 }
883
884 <span class="code-keyword">public</span> BundleContext getContext()
885 {
886 <span class="code-keyword">return</span> m_context;
887 }
888}
889</pre>
890</div></div>
891
892<p>With this bundle activator, the host application can use command
893services provided by bundles installed inside its embedded Felix
894framework instance. The following code snippet illustrates one possible
895approach:</p>
896
897<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
898<pre class="code-java"><span class="code-keyword">package</span> host.core;
899
900<span class="code-keyword">import</span> java.util.List;
901<span class="code-keyword">import</span> java.util.ArrayList;
902<span class="code-keyword">import</span> java.util.Map;
903<span class="code-keyword">import</span> host.service.command.Command;
904<span class="code-keyword">import</span> org.apache.felix.framework.Felix;
905<span class="code-keyword">import</span> org.apache.felix.framework.util.FelixConstants;
906<span class="code-keyword">import</span> org.apache.felix.framework.cache.BundleCache;
907<span class="code-keyword">import</span> org.osgi.framework.Constants;
908<span class="code-keyword">import</span> org.osgi.util.tracker.ServiceTracker;
909
910<span class="code-keyword">public</span> class HostApplication
911{
912 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
913 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
914 <span class="code-keyword">private</span> ServiceTracker m_tracker = <span class="code-keyword">null</span>;
915
916 <span class="code-keyword">public</span> HostApplication()
917 {
918 <span class="code-comment">// Create a configuration property map.
919</span> Map configMap = <span class="code-keyword">new</span> HashMap();
920 <span class="code-comment">// Export the host provided service <span class="code-keyword">interface</span> <span class="code-keyword">package</span>.
921</span> configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
922 <span class="code-quote">"host.service.command; version=1.0.0"</span>);
923 <span class="code-comment">// Create host activator;
924</span> m_activator = <span class="code-keyword">new</span> HostActivator();
925 List list = <span class="code-keyword">new</span> ArrayList();
926 list.add(m_activator);
927 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
928
929 <span class="code-keyword">try</span>
930 {
931 <span class="code-comment">// Now create an instance of the framework with
932</span> <span class="code-comment">// our configuration properties.
933</span> m_felix = <span class="code-keyword">new</span> Felix(configMap);
934 <span class="code-comment">// Now start Felix instance.
935</span> m_felix.start();
936 }
937 <span class="code-keyword">catch</span> (Exception ex)
938 {
939 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
940 ex.printStackTrace();
941 }
942
943 m_tracker = <span class="code-keyword">new</span> ServiceTracker(
944 m_activator.getContext(), Command.class.getName(), <span class="code-keyword">null</span>);
945 m_tracker.open();
946 }
947
948 <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)
949 {
950 <span class="code-comment">// See <span class="code-keyword">if</span> any of the currently tracked command services
951</span> <span class="code-comment">// match the specified command name, <span class="code-keyword">if</span> so then execute it.
952</span> <span class="code-object">Object</span>[] services = m_tracker.getServices();
953 <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++)
954 {
955 <span class="code-keyword">try</span>
956 {
957 <span class="code-keyword">if</span> (((Command) services[i]).getName().equals(name))
958 {
959 <span class="code-keyword">return</span> ((Command) services[i]).execute(commandline);
960 }
961 }
962 <span class="code-keyword">catch</span> (Exception ex)
963 {
964 <span class="code-comment">// Since the services returned by the tracker could become
965</span> <span class="code-comment">// invalid at any moment, we will <span class="code-keyword">catch</span> all exceptions, log
966</span> <span class="code-comment">// a message, and then ignore faulty services.
967</span> <span class="code-object">System</span>.err.println(ex);
968 }
969 }
970 <span class="code-keyword">return</span> <span class="code-keyword">false</span>;
971 }
972
973 <span class="code-keyword">public</span> void shutdownApplication()
974 {
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]975 <span class="code-comment">// Shut down the felix framework when stopping the
976</span> <span class="code-comment">// host application.
977</span> m_felix.stop();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]978 m_felix.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]979 }
980}
981</pre>
982</div></div>
983
984<p>The above example is overly simplistic with respect to concurrency
985issues and error conditions, but it demonstrates the overall approach
986for using bundle-provided services from the host application.</p>
987
988<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-servicereflection"></a></p>
989
990<h3><a name="ApacheFelixFrameworkLaunchingandEmbedding-UsingBundleServicesviaReflection"></a>Using Bundle Services via Reflection</h3>
991
992<p>It possible for the host application to use services provided by
993bundles without having access to the service interface classes and thus
994not needing to put the service interface classes on the class path. To
995do this, the host application uses the same general approach to acquire
996the system bundle context object, which it can use to look up service
997objects. Using either an LDAP filter or the service interface class
998name, the host application can retrieve the service object and then use
999standard Java reflection to invoke methods on the service object.</p>
1000
1001<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-serviceother"></a></p>
1002
1003<h3><a name="ApacheFelixFrameworkLaunchingandEmbedding-OtherApproaches"></a>Other Approaches</h3>
1004
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]1005<p>The <a href="http://code.google.com/p/transloader/" class="external-link" rel="nofollow">Transloader</a> project is another attempt at dealing with issues of classes loaded from different class loaders and may be of interest.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]1006
1007<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-caveat"></a></p>
1008
1009<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-Caveat"></a>Caveat</h1>
1010
1011<p>The code in this document has not been thoroughly tested nor even
1012compiled and may be out of date with respect to the current Felix
1013source code. If you find errors please report them so the that they can
1014be corrected.</p>
1015
1016<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-feedback"></a></p>
1017
1018<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-Feedback"></a>Feedback</h2>
1019
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]1020<p>Subscribe to the Felix users mailing list by sending a message to <a href="mailto:users-subscribe@felix.apache.org" class="external-link" rel="nofollow">users-subscribe@felix.apache.org</a>; after subscribing, email questions or feedback to <a href="mailto:users@felix.apache.org" class="external-link" rel="nofollow">users@felix.apache.org</a>.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]1021 </div>
Karl Pauls424d5a62010-12-26 21:11:45 +0000[diff] [blame^]1022 </body></html>