Gitiles
Code Review Sign In
gerrit.onosproject.org / onos-felix / 7e0316bbb285c499f512c244b53fa00e52b6b64d / . / main.distribution / doc / apache-felix-framework-launching-and-embedding.html
blob: 533f42c520c152513061ca956691f660de47b791 [file] [log] [blame]
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
2<html><head>
3
4
5
6 <title>Apache Felix - Apache Felix Framework Launching and Embedding</title>
7 <link rel="stylesheet" href="apache-felix-framework-launching-and-embedding_files/site.css" type="text/css" media="all">
8 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
9 </head><body>
10 <div class="title"><div class="logo"><a href="http://felix.apache.org/site/index.html"><img alt="Apache Felix" src="apache-felix-framework-launching-and-embedding_files/logo.png" border="0"></a></div><div class="header"><a href="http://www.apache.org/"><img alt="Apache" src="apache-felix-framework-launching-and-embedding_files/apache.png" border="0"></a></div></div>
11 <div class="menu">
12<ul>
13 <li><a href="http://felix.apache.org/site/news.html" title="news">news</a></li>
14 <li><a href="http://felix.apache.org/site/license.html" title="license">license</a></li>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]15 <li><a href="http://felix.apache.org/site/downloads.cgi" class="external-link" rel="nofollow">downloads</a></li>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]16 <li><a href="http://felix.apache.org/site/documentation.html" title="documentation">documentation</a></li>
17 <li><a href="http://felix.apache.org/site/mailinglists.html" title="mailinglists">mailing lists</a></li>
18 <li><a href="http://felix.apache.org/site/contributing.html" title="Contributing">contributing</a></li>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]19 <li><a href="http://www.apache.org/" class="external-link" rel="nofollow">asf</a></li>
20 <li><a href="http://www.apache.org/foundation/sponsorship.html" class="external-link" rel="nofollow">sponsorship</a></li>
21 <li><a href="http://www.apache.org/foundation/thanks.html" class="external-link" rel="nofollow">sponsors</a>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]22<!-- ApacheCon Ad -->
23<iframe src="apache-felix-framework-launching-and-embedding_files/button.html" style="border-width: 0pt; float: left;" frameborder="0" height="135" scrolling="no" width="135"></iframe>
24<p style="height: 100px;">
25<!-- ApacheCon Ad -->
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]26</p></li></ul>
27 </div>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]28 <div class="main">
29<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-ApacheFelixFrameworkLaunchingandEmbedding"></a>Apache Felix Framework Launching and Embedding</h1>
30
31<p><em>[This document describes framework launching introduced in Felix
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]32Framework 2.0.0 and continuing with the latest releases; it is
33incompatible with older versions of the Felix framework.]</em></p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]34
35<ul>
36 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-introduction">Introduction</a></li>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]37 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-overview">OSGi Launching and Embedding API Overview</a>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]38 <ul>
39 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-creatingandconfiguring">Creating and Configuring the Framework Instance</a></li>
40 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-startinginstance">Starting the Framework Instance</a></li>
41 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-stoppinginstance">Stopping the Framework Instance</a></li>
42 </ul>
43 </li>
44 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-launching">Launching Felix</a>
45 <ul>
46 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-standardlauncher">Standard Felix Launcher</a></li>
47 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-customlauncher">Custom Felix Launcher</a></li>
48 </ul>
49 </li>
50 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-embedding">Embedding Felix</a>
51 <ul>
52 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction">Host/Felix Interaction</a></li>
53 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostservices">Providing Host Application Services</a></li>
54 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostserviceusage">Using Services Provided by Bundles</a>
55 <ul>
56 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-servicereflection">Using Bundle Services via Reflection</a></li>
57 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-serviceother">Other Approaches</a></li>
58 </ul>
59 </li>
60 </ul>
61 </li>
62 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-caveat">Caveat</a></li>
63 <li><a href="#ApacheFelixFrameworkLaunchingandEmbedding-feedback">Feedback</a></li>
64</ul>
65
66
67<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-introduction"></a></p>
68
69<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-Introduction"></a>Introduction</h1>
70
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]71<p>The Apache Felix Framework is intended to be easily launchable and
72embeddable. For example, the Felix framework implementation avoids the
73use of system properties for configuration, since these are globals and
74can cause interference if multiple framework instances are created in
75the same VM. The framework also tries to multiplex singleton
76facilities, like the URL stream handler factory. The goal is to make it
77possible to use the framework in a variety of scenarios; however, this
78is still just a goal. In other words, this is a work in progress and if
79any issues arise, it would be greatly appreciated if they are brought
80to the attention of the Felix community. The next section provides an
81overview of the standard OSGi launching and embedding API for
82frameworks, while the remainder of the document is divided into two
83sections, one focusing on how to launch Felix and one focusing on how
84to embed Felix into a host application.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]85
86<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-overview"></a></p>
87
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]88<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-OSGiLaunchingandEmbeddingAPIOverview"></a>OSGi Launching and Embedding API Overview</h1>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]89
90<p>The Felix framework is implemented by the <tt>org.apache.felix.framework.Felix</tt> class or just <tt>Felix</tt>
91for short. As part of the R4.2 OSGi specification, the launching and
92embedding API of the OSGi framework has been standardized. The approach
93is 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>
94
95<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
96<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> Bundle
97{
98 BundleContext getBundleContext();
99 <span class="code-object">long</span> getBundleId();
100 URL getEntry(<span class="code-object">String</span> name);
101 Enumeration getEntryPaths(<span class="code-object">String</span> path);
102 Enumeration findEntries(<span class="code-object">String</span> path, <span class="code-object">String</span> filePattern, <span class="code-object">boolean</span> recurse);
103 Dictionary getHeaders();
104 Dictionary getHeaders(<span class="code-object">String</span> locale);
105 <span class="code-object">long</span> getLastModified();
106 <span class="code-object">String</span> getLocation();
107 URL getResource(<span class="code-object">String</span> name);
108 Enumeration getResources(<span class="code-object">String</span> name) <span class="code-keyword">throws</span> IOException;
109 ServiceReference[] getRegisteredServices();
110 ServiceReference[] getServicesInUse();
111 <span class="code-object">int</span> getState();
112 <span class="code-object">String</span> getSymbolicName();
113 Version getVersion();
114 <span class="code-object">boolean</span> hasPermission(<span class="code-object">Object</span> obj);
115 <span class="code-object">Class</span> loadClass(<span class="code-object">String</span> name) <span class="code-keyword">throws</span> ClassNotFoundException;
116 void start() <span class="code-keyword">throws</span> BundleException;
117 void stop() <span class="code-keyword">throws</span> BundleException;
118 void uninstall() <span class="code-keyword">throws</span> BundleException;
119 void update() <span class="code-keyword">throws</span> BundleException;
120 void update(InputStream is) <span class="code-keyword">throws</span> BundleException;
121}
122</pre>
123</div></div>
124
125<p>The <tt>Framework</tt> interface is defined as:</p>
126
127<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
128<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> Framework <span class="code-keyword">extends</span> Bundle
129{
130 void init();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]131 FrameworkEvent waitForStop(<span class="code-object">long</span> timeout);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]132}
133</pre>
134</div></div>
135
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]136<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]137
138<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
139<pre class="code-java"><span class="code-keyword">public</span> <span class="code-keyword">interface</span> FrameworkFactory
140{
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]141 Framework newFramework(Map config);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]142}
143</pre>
144</div></div>
145
146<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>
147
148<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-creatingandconfiguring"></a></p>
149
150<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-CreatingandConfiguringtheFrameworkInstance"></a>Creating and Configuring the Framework Instance</h2>
151
152<p>You use the framework factory to construct and configure a framework
153instance (or by directly instantiating the Felix class). The
154configuration map may contain the following OSGi standard properties:</p>
155
156<ul>
157 <li><tt>org.osgi.framework.system.packages</tt> - specifies a
158list of packages the system bundle should export from the environment;
159if this is not set, then the framework uses a reasonable default fault.</li>
160 <li><tt>org.osgi.framework.system.packages.extra</tt>
161- specifies a list of additional packages the system bundle should
162export from the environment that are appended to the packages specified
163in <tt>org.osgi.framework.system.packages</tt>; there is no default value for this property.</li>
164 <li><tt>org.osgi.framework.bootdelegation</tt>
165- specifies a list of packages that should be made implicitly available
166to all bundles from the environment (i.e., no need to import them);
167there is no default value for this property and its use should be
168avoided.</li>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]169 <li><tt>org.osgi.framework.bundle.parent</tt> - Specifies which class loader is used for boot delegation. Possible values are: <tt>boot</tt> for the boot class loader, <tt>app</tt> for the application class loader, <tt>ext</tt> for the extension class loader, and <tt>framework</tt> for the framework's class loader. The default is <tt>boot</tt>.</li>
170 <li><tt>org.osgi.framework.storage</tt>
171- specifies the path to a directory, which will be created if it does
172not exist, to use for bundle cache storage; the default value for this
173property is "<tt>felix-cache</tt>" in the current working directory.</li>
174 <li><tt>org.osgi.framework.storage.clean</tt> - specifies whether the bundle cache should be flushed; the default value for this property is "<tt>none</tt>", but it can be changed to "<tt>onFirstInit</tt>" to flush the bundle cache when the framework is initialized.</li>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]175 <li><tt>org.osgi.framework.startlevel.beginning</tt> - specifies the start level the framework enters upon startup; the default value for this property is 1.</li>
176</ul>
177
178
179<p>Felix also has the following, non-standard configuration properties:</p>
180
181<ul>
182 <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>
183 <li><tt>felix.systembundle.activators</tt> - specifies a <tt>List</tt> of <tt>BundleActivator</tt>
184instances that are started/stopped when the System Bundle is
185started/stopped; the specified instances will receive the System
186Bundle's <tt>BundleContext</tt> when invoked.</li>
187 <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>
188 <li><tt>felix.log.level</tt> - specifies an integer <tt>String</tt>
189whose value indicates the degree of logging reported by the framework;
190the default value is "1" and "0" turns off logging completely,
191otherwise log levels match those specified in the OSGi Log Service
192(i.e., 1 = error, 2 = warning, 3 = information, and 4 = debug).</li>
193 <li><tt>felix.startlevel.bundle</tt> - specifies the start level for newly installed bundles; the default value is 1.</li>
194 <li><tt>felix.bootdelegation.implicit</tt>
195- specifies whether or not the framework should try to guess when to
196boot delegate when external code tries to load classes or resources;
197the default value is "<tt>true</tt>".</li>
198 <li><tt>framework.service.urlhandlers</tt> - specifies whether or not to activate the URL Handlers service for the framework instance; the default value is "<tt>true</tt>", which results in the <tt>URL.setURLStreamHandlerFactory()</tt> and <tt>URLConnection.setContentHandlerFactory()</tt> being called.</li>
199</ul>
200
201
202<p>The configuration map is copied and the keys are treated as case
203insensitive. You are not able to change the framework's configuration
204after construction. If you need a different configuration, you must
205create a new framework instance.</p>
206
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]207<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-usage-documentation.html#ApacheFelixFrameworkUsageDocumentation-migrating">usage document</a> describes the configuration property changes.</td></tr></tbody></table></div>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]208
209<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-startinginstance"></a></p>
210
211<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StartingtheFrameworkInstance"></a>Starting the Framework Instance</h2>
212
213<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>
214
215<ul>
216 <li><tt>init()</tt> results in the framework instance in the <tt>Bundle.STARTING</tt> state.</li>
217 <li><tt>start()</tt> results in the framework instance in the <tt>Bundle.ACTIVE</tt> state.</li>
218</ul>
219
220
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]221<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]222
223<ul>
224 <li>Event handling is enabled.</li>
225 <li>The security manager is installed if it is enabled.</li>
226 <li>The framework is set to start level 0.</li>
227 <li>All bundles in the bundle caches are reified and their state is set to <tt>Bundle.INSTALLED</tt>.</li>
228 <li>The framework gets a valid <tt>BundleContext</tt>.</li>
229 <li>All framework-provided services are made available (e.g., PackageAdmin, StartLevel, etc.).</li>
230 <li>The framework enters the <tt>Bundle.STARTING</tt> state.</li>
231</ul>
232
233
234<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>
235
236<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-stoppinginstance"></a></p>
237
238<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StoppingtheFrameworkInstance"></a>Stopping the Framework Instance</h2>
239
240<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>
241
242<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-launching"></a></p>
243
244<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-LaunchingaFramework"></a>Launching a Framework</h1>
245
246<p>Launching a framework is fairly simple and involves only four steps:</p>
247
248<ol>
249 <li>Define some configuration properties.</li>
250 <li>Obtain framework factory.</li>
251 <li>Use factory to create framework with the configuration properties.</li>
252 <li>Invoke the <tt>Framework.start()</tt> method.</li>
253</ol>
254
255
256<p>In reality, the first step is optional, since all properties will
257have reasonable defaults, but if you are creating a launcher you will
258generally want to more than that, such as automatically installing and
259starting bundles when you start the framework instance. The default
260Felix launcher defines reusable functionality to automatically install
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]261and/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]262
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]263<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]264
265<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-standardlauncher"></a></p>
266
267<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-StandardFelixFrameworkLauncher"></a>Standard Felix Framework Launcher</h2>
268
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]269<p>The standard Felix framework launcher is very simple and is not
270intended to solve every possible requirement; it is intended to work
271for most standard situations. Most special launching requirements
272should be resolved by creating a custom launcher. This section
273describes how the standard launcher works. The following code
274represents 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]275
276<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
277<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
278{
279 <span class="code-comment">// (1) Check <span class="code-keyword">for</span> command line arguments and verify usage.
280</span> <span class="code-object">String</span> bundleDir = <span class="code-keyword">null</span>;
281 <span class="code-object">String</span> cacheDir = <span class="code-keyword">null</span>;
282 <span class="code-object">boolean</span> expectBundleDir = <span class="code-keyword">false</span>;
283 <span class="code-keyword">for</span> (<span class="code-object">int</span> i = 0; i &lt; args.length; i++)
284 {
285 <span class="code-keyword">if</span> (args[i].equals(BUNDLE_DIR_SWITCH))
286 {
287 expectBundleDir = <span class="code-keyword">true</span>;
288 }
289 <span class="code-keyword">else</span> <span class="code-keyword">if</span> (expectBundleDir)
290 {
291 bundleDir = args[i];
292 expectBundleDir = <span class="code-keyword">false</span>;
293 }
294 <span class="code-keyword">else</span>
295 {
296 cacheDir = args[i];
297 }
298 }
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]299
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]300 <span class="code-keyword">if</span> ((args.length &gt; 3) || (expectBundleDir &amp;&amp; bundleDir == <span class="code-keyword">null</span>))
301 {
302 <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>);
303 <span class="code-object">System</span>.exit(0);
304 }
305
306 <span class="code-comment">// (2) Load system properties.
307</span> Main.loadSystemProperties();
308
309 <span class="code-comment">// (3) Read configuration properties.
310</span> Properties configProps = Main.loadConfigProperties();
311 <span class="code-keyword">if</span> (configProps == <span class="code-keyword">null</span>)
312 {
313 <span class="code-object">System</span>.err.println(<span class="code-quote">"No "</span> + CONFIG_PROPERTIES_FILE_VALUE + <span class="code-quote">" found."</span>);
314 configProps = <span class="code-keyword">new</span> Properties();
315 }
316
317 <span class="code-comment">// (4) Copy framework properties from the system properties.
318</span> Main.copySystemProperties(configProps);
319
320 <span class="code-comment">// (5) Use the specified auto-deploy directory over <span class="code-keyword">default</span>.
321</span> <span class="code-keyword">if</span> (bundleDir != <span class="code-keyword">null</span>)
322 {
323 configProps.setProperty(AutoProcessor.AUTO_DEPLOY_DIR_PROPERY, bundleDir);
324 }
325
326 <span class="code-comment">// (6) Use the specified bundle cache directory over <span class="code-keyword">default</span>.
327</span> <span class="code-keyword">if</span> (cacheDir != <span class="code-keyword">null</span>)
328 {
329 configProps.setProperty(Constants.FRAMEWORK_STORAGE, cacheDir);
330 }
331
332 <span class="code-comment">// (7) Add a shutdown hook to clean stop the framework.
333</span> <span class="code-object">String</span> enableHook = configProps.getProperty(SHUTDOWN_HOOK_PROP);
334 <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>))
335 {
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]336 <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]337 <span class="code-keyword">public</span> void run()
338 {
339 <span class="code-keyword">try</span>
340 {
341 <span class="code-keyword">if</span> (m_fwk != <span class="code-keyword">null</span>)
342 {
343 m_fwk.stop();
344 m_fwk.waitForStop(0);
345 }
346 }
347 <span class="code-keyword">catch</span> (Exception ex)
348 {
349 <span class="code-object">System</span>.err.println(<span class="code-quote">"Error stopping framework: "</span> + ex);
350 }
351 }
352 });
353 }
354
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]355 <span class="code-keyword">try</span>
356 {
357 <span class="code-comment">// (8) Create an instance and initialize the framework.
358</span> FrameworkFactory factory = getFrameworkFactory();
359 m_fwk = factory.newFramework(configProps);
360 m_fwk.init();
361 <span class="code-comment">// (9) Use the system bundle context to process the auto-deploy
362</span> <span class="code-comment">// and auto-install/auto-start properties.
363</span> AutoProcessor.process(configProps, m_fwk.getBundleContext());
364 <span class="code-comment">// (10) Start the framework.
365</span> m_fwk.start();
366 <span class="code-comment">// (11) Wait <span class="code-keyword">for</span> framework to stop to exit the VM.
367</span> m_fwk.waitForStop(0);
368 <span class="code-object">System</span>.exit(0);
369 }
370 <span class="code-keyword">catch</span> (Exception ex)
371 {
372 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
373 ex.printStackTrace();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]374 <span class="code-object">System</span>.exit(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]375 }
376}
377</pre>
378</div></div>
379
380<p>The general steps of the standard launcher are quite straightforward:</p>
381
382<ol>
383 <li>The launcher supports setting the auto-deploy directory (with the <tt>-b</tt>
384switch) and setting the bundle cache path with a single argument, so
385check for this and issue a usage message it there are more than one
386arguments.</li>
387 <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>
388system property. This file is not needed to launch Felix and is
389provided merely for convenience when system properties must be
390specified. The file is a standard Java properties file, but it also
391supports property substitution using <tt>${&lt;property-name</tt>} syntax. Property substitution can be nested; only system properties will be used for substitution.</li>
392 <li>Load any configuration properties specified in the <tt>config.properties</tt> file; this file is typically located in the <tt>conf/</tt> directory of the Felix installation directory, but it can be specified directly using the <tt>felix.config.properties</tt>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]393system property. This file is used to configure the framework instance
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]394created by the launcher. The file is a standard Java properties file,
395but it also supports property substitution using "<tt>${&lt;property-name&gt;</tt>}"
396syntax. Property substitution can be nested; configuration and system
397properties will be used for substitution with configuration properties
398having precedence.</li>
399 <li>For convenience, any configuration
400properties that are set as system properties are copied into the set of
401configuration properties. This provide an easy way to add to or
402override configuration properties specified in the <tt>config.properties</tt> file, since the Felix instance will never look at system properties for configuration.</li>
403 <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>
404 <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>
405 <li>Add a shutdown hook to cleanly stop the framework, unless the hook is disabled.</li>
406 <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>
407 <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>
408configuration properties during framework startup to automatically
409install and/or start bundles; see the usage document for more
410information <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>
411 <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>
412</ol>
413
414
415<p>The framework is not active until the <tt>start()</tt> method is
416called. If no shell bundles are installed and started or if there is
417difficulty locating the shell bundles specified in the auto-start
418property, then it will appear as if the framework is hung, but it is
419actually running without any way to interact with it since the shell
420bundles provide the only means of interaction.</p>
421
422<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-customlauncher"></a></p>
423
424<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-CustomFrameworkLauncher"></a>Custom Framework Launcher</h2>
425
426<p>This section creates a bare-bones launcher to demonstrate the
427minimum requirements for creating an interactive launcher for the Felix
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]428framework. This example uses the standard Gogo shell bundles for
429interactivity, but any other bundles could be used instead. This
430example launcher project has the following directory structure:</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]431
432<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
433<pre>launcher/
434 lib/
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]435 org.apache.felix.main-3.0.0.jar
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]436 bundle/
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]437 org.apache.felix.gogo.command-0.6.0.jar
438 org.apache.felix.gogo.runtime-0.6.0.jar
439 org.apache.felix.gogo.shell-0.6.0.jar
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]440 src/
441 example/
442 Main.java
443</pre>
444</div></div>
445
446<p>The <tt>lib/</tt> directory contains Felix' main JAR file, which
447also contains the OSGi core interfaces. The main JAR file is used so
448that we can reuse the default launcher's auto-install/auto-start
449configuration property handling; if these capabilities are not needed,
450then it would be possible to use the framework JAR file instead of the
451main JAR file. The <tt>bundle/</tt> directory contains the shell
452service and textual shell interface bundles that will be used for
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]453interacting with the framework instance. Note: If you do not launch the
454framework with interactive bundles, it will appear as if the framework
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]455instance is hung, but it is actually just sitting there waiting for
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]456someone 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]457
458<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
459<pre class="code-java"><span class="code-keyword">package</span> example;
460
461<span class="code-keyword">import</span> java.io.*;
462<span class="code-keyword">import</span> org.osgi.framework.launch.*;
463<span class="code-keyword">import</span> org.apache.felix.main.AutoProcessor;
464
465<span class="code-keyword">public</span> class Main
466{
467 <span class="code-keyword">private</span> <span class="code-keyword">static</span> Framework m_fwk = <span class="code-keyword">null</span>;
468
469 <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
470 {
471 <span class="code-comment">// Print welcome banner.
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]472</span> <span class="code-object">System</span>.out.println(<span class="code-quote">"\nWelcome to My Launcher"</span>);
473 <span class="code-object">System</span>.out.println(<span class="code-quote">"======================\n"</span>);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]474
475 <span class="code-keyword">try</span>
476 {
477 m_fwk = getFrameworkFactory().newFramework(<span class="code-keyword">null</span>);
478 m_fwk.init()
479 AutoProcessor.process(<span class="code-keyword">null</span>, m_fwk.getBundleContext());
480 m_fwk.start();
481 m_fwk.waitForStop();
482 <span class="code-object">System</span>.exit(0);
483 }
484 <span class="code-keyword">catch</span> (Exception ex)
485 {
486 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
487 ex.printStackTrace();
488 <span class="code-object">System</span>.exit(-1);
489 }
490 }
491
492 <span class="code-keyword">private</span> <span class="code-keyword">static</span> FrameworkFactory getFrameworkFactory() <span class="code-keyword">throws</span> Exception
493 {
494 URL url = Main.class.getClassLoader().getResource(
495 <span class="code-quote">"META-INF/services/org.osgi.framework.launch.FrameworkFactory"</span>);
496 <span class="code-keyword">if</span> (url != <span class="code-keyword">null</span>)
497 {
498 BufferedReader br = <span class="code-keyword">new</span> BufferedReader(<span class="code-keyword">new</span> InputStreamReader(url.openStream()));
499 <span class="code-keyword">try</span>
500 {
501 <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())
502 {
503 s = s.trim();
504 <span class="code-comment">// Try to load first non-empty, non-commented line.
505</span> <span class="code-keyword">if</span> ((s.length() &gt; 0) &amp;&amp; (s.charAt(0) != '#'))
506 {
507 <span class="code-keyword">return</span> (FrameworkFactory) <span class="code-object">Class</span>.forName(s).newInstance();
508 }
509 }
510 }
511 <span class="code-keyword">finally</span>
512 {
513 <span class="code-keyword">if</span> (br != <span class="code-keyword">null</span>) br.close();
514 }
515 }
516
517 <span class="code-keyword">throw</span> <span class="code-keyword">new</span> Exception(<span class="code-quote">"Could not find framework factory."</span>);
518 }
519}
520</pre>
521</div></div>
522
523<p>This launcher relies on the default behavior of <tt>AutoProcessor</tt>
524to automatically deploy the shell bundles. This simple, generic
525launcher provides a good starting point if the default Felix launcher
526is not sufficient. Since very few configuration properties are
527specified, the default values are used. For the bundle auto-deploy
528directory, "<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>
529
530<p>By breaking down the above source code into small chunks, it is quite easy to see what is going on.</p>
531
532<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
533<pre class="code-java"> m_fwk = getFrameworkFactory().newFramework(<span class="code-keyword">null</span>);
534 m_fwk.init()
535</pre>
536</div></div>
537
538<p>These steps get a the framework factory service and use it to create
539a framework instance with a default configuration. Once the framework
540instance is created, it is initialized with <tt>init()</tt>.</p>
541
542<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
543<pre class="code-java"> AutoProcessor.process(<span class="code-keyword">null</span>, m_fwk.getBundleContext());
544</pre>
545</div></div>
546
547<p>The <tt>AutorProcessor</tt> will automatically deploy bundles in the
548auto-deploy directory and any referenced from the auto-install/start
549properties. Since we are using an empty configuration, the auto-deploy
550directory is the <tt>bundle</tt> directory in the current directory
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]551and there are no auto properties. Therefore, in this case, the shell
552bundles will be installed.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]553
554<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
555<pre class="code-java"> m_fwk.start();
556 m_fwk.waitForStop();
557 <span class="code-object">System</span>.exit(0);
558</pre>
559</div></div>
560
561<p>These final steps start the framework and cause the launching
562application thread to wait for the framework to stop and when it does
563the launching thread calls <tt>System.exit()</tt> to make sure the VM actually exits.</p>
564
565<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
566<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
567 {
568 ...
569 }
570</pre>
571</div></div>
572
573<p>This method retrieves the framework factory service by doing a
574META-INF/services resource lookup, which it can use to obtain the
575concrete class name for the factory. If you are using Java 6, then you
576can use the <tt>ServiceLoader</tt> API in the JRE to further simplify the factory service lookup.</p>
577
578<p>The following command compiles the launcher when run from the root directory of the launcher project:</p>
579
580<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]581<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]582</pre>
583</div></div>
584
585<p>After executing this command, an <tt>example/</tt> directory is
586created in the current directory, which contains the generated class
587file. The following command executes the simple launcher when run from
588the root directory of the launcher project:</p>
589
590<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]591<pre>java -cp .:lib/org.apache.felix.main-3.0.0.jar example.Main
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]592</pre>
593</div></div>
594
595<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>
596
597<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-embedding"></a></p>
598
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]599<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-EmbeddingtheFelixFramework"></a>Embedding the Felix Framework</h1>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]600
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]601<p>Embedding the Felix framework into a host application is a simple
602way to provide a sophisticated extensibility mechanism (i.e., a plugin
603system) to the host application. Embedding the Felix framework is very
604similar to launching it as described above, the main difference is that
605the host application typically wants to interact with the framework
606instance and/or installed bundles/services from the outside. This is
607fairly easy to achieve, but there are some subtle issues to understand.
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]608This section presents the mechanisms for embedding Felix into a host
609application and the issues in doing so.</p>
610
611<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction"></a></p>
612
613<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-Host/FelixInteraction"></a>Host/Felix Interaction</h2>
614
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]615<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]616which is a list of bundle activator instances. These bundle activator
617instances provide a convenient way for host applications to interact
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]618with the Felix framework.</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]619
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]620<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>
621configuration property is specific to the Felix framework
622implementation. If you want your code to work with other framework
623implementations, 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>
624
625<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]626
627<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
628<pre class="code-java"><span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
629{
630 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
631
632 <span class="code-keyword">public</span> void start(BundleContext context)
633 {
634 m_context = context;
635 }
636
637 <span class="code-keyword">public</span> void stop(BundleContext context)
638 {
639 m_context = <span class="code-keyword">null</span>;
640 }
641
642 <span class="code-keyword">public</span> Bundle[] getBundles()
643 {
644 <span class="code-keyword">if</span> (m_context != <span class="code-keyword">null</span>)
645 {
646 <span class="code-keyword">return</span> m_context.getBundles();
647 }
648 <span class="code-keyword">return</span> <span class="code-keyword">null</span>;
649 }
650}
651</pre>
652</div></div>
653
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]654<p>Given the above bundle activator, it is now possible to embed the
655Felix framework into a host application and interact with it as the
656following snippet illustrates:</p>
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]657
658<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
659<pre class="code-java"><span class="code-keyword">public</span> class HostApplication
660{
661 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
662 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
663
664 <span class="code-keyword">public</span> HostApplication()
665 {
666 <span class="code-comment">// Create a configuration property map.
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]667</span> Map config = <span class="code-keyword">new</span> HashMap();
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]668 <span class="code-comment">// Create host activator;
669</span> m_activator = <span class="code-keyword">new</span> HostActivator();
670 List list = <span class="code-keyword">new</span> ArrayList();
671 list.add(m_activator);
672 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
673
674 <span class="code-keyword">try</span>
675 {
676 <span class="code-comment">// Now create an instance of the framework with
677</span> <span class="code-comment">// our configuration properties.
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]678</span> m_felix = <span class="code-keyword">new</span> Felix(config);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]679 <span class="code-comment">// Now start Felix instance.
680</span> m_felix.start();
681 }
682 <span class="code-keyword">catch</span> (Exception ex)
683 {
684 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
685 ex.printStackTrace();
686 }
687 }
688
689 <span class="code-keyword">public</span> Bundle[] getInstalledBundles()
690 {
691 <span class="code-comment">// Use the system bundle activator to gain external
692</span> <span class="code-comment">// access to the set of installed bundles.
693</span> <span class="code-keyword">return</span> m_activator.getBundles();
694 }
695
696 <span class="code-keyword">public</span> void shutdownApplication()
697 {
698 <span class="code-comment">// Shut down the felix framework when stopping the
699</span> <span class="code-comment">// host application.
700</span> m_felix.stop();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]701 m_felix.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]702 }
703}
704</pre>
705</div></div>
706
707<p>Notice how the <tt>HostApplication.getInstalledBundles()</tt> method
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]708uses its activator instance to get access to the system bundle's
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]709context in order to interact with the embedded Felix framework
710instance. This approach provides the foundation for all interaction
711between the host application and the embedded framework instance.</p>
712
713<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostservices"></a></p>
714
715<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-ProvidingHostApplicationServices"></a>Providing Host Application Services</h2>
716
717<p>Providing services from the host application to bundles inside the
718embedded Felix framework instance follows the basic approach laid out
719in <a href="#ApacheFelixFrameworkLaunchingandEmbedding-hostinteraction">above</a>.
720The main complication for providing a host application service to
721bundles is the fact that both the host application and the bundles must
722be using the same class definitions for the service interface classes.
723Since the host application cannot import classes from a bundle, this
724means that the service interface classes <b>must</b> be accessible on
725the class path, typically as part of the host application itself. The
726host application then must export the service interface package via the
727system bundle so that bundles installed into the embedded framework
728instance can import it. This is achieved using the <tt>org.osgi.framework.system.packages.extra</tt> configuration property previously presented.</p>
729
730<p>Consider the follow simple property lookup service:</p>
731
732<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
733<pre class="code-java"><span class="code-keyword">package</span> host.service.lookup;
734
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]735<span class="code-keyword">public</span> <span class="code-keyword">interface</span> Lookup
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]736{
737 <span class="code-keyword">public</span> <span class="code-object">Object</span> lookup(<span class="code-object">String</span> name);
738}
739</pre>
740</div></div>
741
742<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>"
743command. Now consider the following host application bundle activator,
744which will be used to register/unregister the property lookup service
745when the embedded framework instance starts/stops:</p>
746
747<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
748<pre class="code-java"><span class="code-keyword">package</span> host.core;
749
750<span class="code-keyword">import</span> java.util.Map;
751<span class="code-keyword">import</span> org.osgi.framework.BundleActivator;
752<span class="code-keyword">import</span> org.osgi.framework.BundleContext;
753<span class="code-keyword">import</span> org.osgi.framework.ServiceRegistration;
754<span class="code-keyword">import</span> host.service.lookup;
755
756<span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
757{
758 <span class="code-keyword">private</span> Map m_lookupMap = <span class="code-keyword">null</span>;
759 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
760 <span class="code-keyword">private</span> ServiceRegistration m_registration = <span class="code-keyword">null</span>;
761
762 <span class="code-keyword">public</span> HostActivator(Map lookupMap)
763 {
764 <span class="code-comment">// Save a reference to the service's backing store.
765</span> m_lookupMap = lookupMap;
766 }
767
768 <span class="code-keyword">public</span> void start(BundleContext context)
769 {
770 <span class="code-comment">// Save a reference to the bundle context.
771</span> m_context = context;
772 <span class="code-comment">// Create a property lookup service implementation.
773</span> Lookup lookup = <span class="code-keyword">new</span> Lookup() {
774 <span class="code-keyword">public</span> <span class="code-object">Object</span> lookup(<span class="code-object">String</span> name)
775 {
776 <span class="code-keyword">return</span> m_lookupMap.get(name);
777 }
778 };
779 <span class="code-comment">// Register the property lookup service and save
780</span> <span class="code-comment">// the service registration.
781</span> m_registration = m_context.registerService(
782 Lookup.class.getName(), lookup, <span class="code-keyword">null</span>);
783 }
784
785 <span class="code-keyword">public</span> void stop(BundleContext context)
786 {
787 <span class="code-comment">// Unregister the property lookup service.
788</span> m_registration.unregister();
789 m_context = <span class="code-keyword">null</span>;
790 }
791}
792</pre>
793</div></div>
794
795<p>Given the above host application bundle activator, the following
796code snippet shows how the host application could create an embedded
797version of the Felix framework and provide the property lookup service
798to installed bundles:</p>
799
800<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
801<pre class="code-java"><span class="code-keyword">package</span> host.core;
802
803<span class="code-keyword">import</span> java.util.List;
804<span class="code-keyword">import</span> java.util.ArrayList;
805<span class="code-keyword">import</span> java.util.Map;
806<span class="code-keyword">import</span> java.util.HashMap;
807<span class="code-keyword">import</span> host.service.lookup.Lookup;
808<span class="code-keyword">import</span> org.apache.felix.framework.Felix;
809<span class="code-keyword">import</span> org.apache.felix.framework.util.FelixConstants;
810<span class="code-keyword">import</span> org.osgi.framework.Constants;
811
812<span class="code-keyword">public</span> class HostApplication
813{
814 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
815 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
816 <span class="code-keyword">private</span> Map m_lookupMap = <span class="code-keyword">new</span> HashMap();
817
818 <span class="code-keyword">public</span> HostApplication()
819 {
820 <span class="code-comment">// Initialize the map <span class="code-keyword">for</span> the property lookup service.
821</span> m_lookupMap.put(<span class="code-quote">"name1"</span>, <span class="code-quote">"value1"</span>);
822
823 m_lookupMap.put(<span class="code-quote">"name2"</span>, <span class="code-quote">"value2"</span>);
824 m_lookupMap.put(<span class="code-quote">"name3"</span>, <span class="code-quote">"value3"</span>);
825 m_lookupMap.put(<span class="code-quote">"name4"</span>, <span class="code-quote">"value4"</span>);
826
827 <span class="code-comment">// Create a configuration property map.
828</span> Map configMap = <span class="code-keyword">new</span> HashMap();
829 <span class="code-comment">// Export the host provided service <span class="code-keyword">interface</span> <span class="code-keyword">package</span>.
830</span> configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
831 <span class="code-quote">"host.service.lookup; version=1.0.0"</span>);
832 <span class="code-comment">// Create host activator;
833</span> m_activator = <span class="code-keyword">new</span> HostActivator(m_lookupMap);
834 List list = <span class="code-keyword">new</span> ArrayList();
835 list.add(m_activator);
836 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
837
838 <span class="code-keyword">try</span>
839 {
840 <span class="code-comment">// Now create an instance of the framework with
841</span> <span class="code-comment">// our configuration properties.
842</span> m_felix = <span class="code-keyword">new</span> Felix(configMap);
843 <span class="code-comment">// Now start Felix instance.
844</span> m_felix.start();
845 }
846 <span class="code-keyword">catch</span> (Exception ex)
847 {
848 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
849 ex.printStackTrace();
850 }
851 }
852
853 <span class="code-keyword">public</span> void shutdownApplication()
854 {
855 <span class="code-comment">// Shut down the felix framework when stopping the
856</span> <span class="code-comment">// host application.
857</span> m_felix.stop();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]858 m_felix.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]859 }
860}
861</pre>
862</div></div>
863
864<p>Rather than having the host application bundle activator register
865the service, it is also possible for the the host application to simply
866get the bundle context from the bundle activator and register the
867service directly, but the presented approach is perhaps a little
868cleaner since it allows the host application to register/unregister the
869service when the system bundle starts/stops.</p>
870
871<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-hostserviceusage"></a></p>
872
873<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-UsingServicesProvidedbyBundles"></a>Using Services Provided by Bundles</h2>
874
875<p>Using services provided by bundles follows the same general approach
876of using a host application bundle activator. The main complication for
877the host application using a service from a bundle is the fact that
878both the host application and the bundle must be using the same class
879definitions for the service interface classes. Since the host
880application cannot import classes from a bundle, this means that the
881service interface classes <b>must</b> be accessible on the class path,
882typically as part of the host application itself. The host application
883then must export the service interface package via the system bundle so
884that bundles installed into the embedded framework instance can import
885it. This is achieved using the <tt>org.osgi.framework.system.packages.extra</tt> configuration property previously presented.</p>
886
887<p>Consider the following simple command service interface for which
888bundles provide implementations, such as might be used to create an
889extensible interactive shell:</p>
890
891<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
892<pre class="code-java"><span class="code-keyword">package</span> host.service.command;
893
894<span class="code-keyword">public</span> class Command
895{
896 <span class="code-keyword">public</span> <span class="code-object">String</span> getName();
897 <span class="code-keyword">public</span> <span class="code-object">String</span> getDescription();
898 <span class="code-keyword">public</span> <span class="code-object">boolean</span> execute(<span class="code-object">String</span> commandline);
899}
900</pre>
901</div></div>
902
903<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>"
904command. Now consider the previously introduced host application bundle
905activator below, which simply provides access to the system bundle
906context:</p>
907
908<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
909<pre class="code-java"><span class="code-keyword">package</span> host.core;
910
911<span class="code-keyword">import</span> org.osgi.framework.BundleActivator;
912<span class="code-keyword">import</span> org.osgi.framework.BundleContext;
913
914<span class="code-keyword">public</span> class HostActivator <span class="code-keyword">implements</span> BundleActivator
915{
916 <span class="code-keyword">private</span> BundleContext m_context = <span class="code-keyword">null</span>;
917
918 <span class="code-keyword">public</span> void start(BundleContext context)
919 {
920 m_context = context;
921 }
922
923 <span class="code-keyword">public</span> void stop(BundleContext context)
924 {
925 m_context = <span class="code-keyword">null</span>;
926 }
927
928 <span class="code-keyword">public</span> BundleContext getContext()
929 {
930 <span class="code-keyword">return</span> m_context;
931 }
932}
933</pre>
934</div></div>
935
936<p>With this bundle activator, the host application can use command
937services provided by bundles installed inside its embedded Felix
938framework instance. The following code snippet illustrates one possible
939approach:</p>
940
941<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
942<pre class="code-java"><span class="code-keyword">package</span> host.core;
943
944<span class="code-keyword">import</span> java.util.List;
945<span class="code-keyword">import</span> java.util.ArrayList;
946<span class="code-keyword">import</span> java.util.Map;
947<span class="code-keyword">import</span> host.service.command.Command;
948<span class="code-keyword">import</span> org.apache.felix.framework.Felix;
949<span class="code-keyword">import</span> org.apache.felix.framework.util.FelixConstants;
950<span class="code-keyword">import</span> org.apache.felix.framework.cache.BundleCache;
951<span class="code-keyword">import</span> org.osgi.framework.Constants;
952<span class="code-keyword">import</span> org.osgi.util.tracker.ServiceTracker;
953
954<span class="code-keyword">public</span> class HostApplication
955{
956 <span class="code-keyword">private</span> HostActivator m_activator = <span class="code-keyword">null</span>;
957 <span class="code-keyword">private</span> Felix m_felix = <span class="code-keyword">null</span>;
958 <span class="code-keyword">private</span> ServiceTracker m_tracker = <span class="code-keyword">null</span>;
959
960 <span class="code-keyword">public</span> HostApplication()
961 {
962 <span class="code-comment">// Create a configuration property map.
963</span> Map configMap = <span class="code-keyword">new</span> HashMap();
964 <span class="code-comment">// Export the host provided service <span class="code-keyword">interface</span> <span class="code-keyword">package</span>.
965</span> configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
966 <span class="code-quote">"host.service.command; version=1.0.0"</span>);
967 <span class="code-comment">// Create host activator;
968</span> m_activator = <span class="code-keyword">new</span> HostActivator();
969 List list = <span class="code-keyword">new</span> ArrayList();
970 list.add(m_activator);
971 configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
972
973 <span class="code-keyword">try</span>
974 {
975 <span class="code-comment">// Now create an instance of the framework with
976</span> <span class="code-comment">// our configuration properties.
977</span> m_felix = <span class="code-keyword">new</span> Felix(configMap);
978 <span class="code-comment">// Now start Felix instance.
979</span> m_felix.start();
980 }
981 <span class="code-keyword">catch</span> (Exception ex)
982 {
983 <span class="code-object">System</span>.err.println(<span class="code-quote">"Could not create framework: "</span> + ex);
984 ex.printStackTrace();
985 }
986
987 m_tracker = <span class="code-keyword">new</span> ServiceTracker(
988 m_activator.getContext(), Command.class.getName(), <span class="code-keyword">null</span>);
989 m_tracker.open();
990 }
991
992 <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)
993 {
994 <span class="code-comment">// See <span class="code-keyword">if</span> any of the currently tracked command services
995</span> <span class="code-comment">// match the specified command name, <span class="code-keyword">if</span> so then execute it.
996</span> <span class="code-object">Object</span>[] services = m_tracker.getServices();
997 <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++)
998 {
999 <span class="code-keyword">try</span>
1000 {
1001 <span class="code-keyword">if</span> (((Command) services[i]).getName().equals(name))
1002 {
1003 <span class="code-keyword">return</span> ((Command) services[i]).execute(commandline);
1004 }
1005 }
1006 <span class="code-keyword">catch</span> (Exception ex)
1007 {
1008 <span class="code-comment">// Since the services returned by the tracker could become
1009</span> <span class="code-comment">// invalid at any moment, we will <span class="code-keyword">catch</span> all exceptions, log
1010</span> <span class="code-comment">// a message, and then ignore faulty services.
1011</span> <span class="code-object">System</span>.err.println(ex);
1012 }
1013 }
1014 <span class="code-keyword">return</span> <span class="code-keyword">false</span>;
1015 }
1016
1017 <span class="code-keyword">public</span> void shutdownApplication()
1018 {
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]1019 <span class="code-comment">// Shut down the felix framework when stopping the
1020</span> <span class="code-comment">// host application.
1021</span> m_felix.stop();
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]1022 m_felix.waitForStop(0);
Karl Paulsc6eda452010-02-14 22:52:56 +0000[diff] [blame]1023 }
1024}
1025</pre>
1026</div></div>
1027
1028<p>The above example is overly simplistic with respect to concurrency
1029issues and error conditions, but it demonstrates the overall approach
1030for using bundle-provided services from the host application.</p>
1031
1032<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-servicereflection"></a></p>
1033
1034<h3><a name="ApacheFelixFrameworkLaunchingandEmbedding-UsingBundleServicesviaReflection"></a>Using Bundle Services via Reflection</h3>
1035
1036<p>It possible for the host application to use services provided by
1037bundles without having access to the service interface classes and thus
1038not needing to put the service interface classes on the class path. To
1039do this, the host application uses the same general approach to acquire
1040the system bundle context object, which it can use to look up service
1041objects. Using either an LDAP filter or the service interface class
1042name, the host application can retrieve the service object and then use
1043standard Java reflection to invoke methods on the service object.</p>
1044
1045<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-serviceother"></a></p>
1046
1047<h3><a name="ApacheFelixFrameworkLaunchingandEmbedding-OtherApproaches"></a>Other Approaches</h3>
1048
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]1049<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]1050
1051<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-caveat"></a></p>
1052
1053<h1><a name="ApacheFelixFrameworkLaunchingandEmbedding-Caveat"></a>Caveat</h1>
1054
1055<p>The code in this document has not been thoroughly tested nor even
1056compiled and may be out of date with respect to the current Felix
1057source code. If you find errors please report them so the that they can
1058be corrected.</p>
1059
1060<p><a name="ApacheFelixFrameworkLaunchingandEmbedding-feedback"></a></p>
1061
1062<h2><a name="ApacheFelixFrameworkLaunchingandEmbedding-Feedback"></a>Feedback</h2>
1063
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]1064<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]1065 </div>
Karl Paulsf4ea0312010-06-06 21:55:08 +0000[diff] [blame]1066 </body></html>