DUE TO SPAM, SIGN-UP IS DISABLED. Goto Selfserve wiki signup and request an account.
Launching and Embedding Apache Felix
...
The Apache Felix OSGi framework is intended to be easily launchable and embeddable. For example, Felix avoids the use of system properties for configuration, since these are globals that can cause interference if multiple framework instances are created in the same VM. Felix is also implemented to multiplex singleton facilities, like the URL stream handler factory. The goal is to make it possible to use Felix in as many scenarios as possible; however, this is still just a goal. In other words, this is a work in progress and if any issues arise, it would be greatly appreciated if they are brought to the attention of the Felix community. The next section provides a Felix API overview, while the remainder of this the document is divided into two main sections, one focusing on how to launch Felix and one focusing on how to embed Felix into a host application.
| Anchor | ||||
|---|---|---|---|---|
|
...
API Overview
Launching Felix is fairly simple and involves only three steps:
...
The Felix class that implements the OSGi framework is org.apache.felix.framework.Felix
...
or just Felix for short. The OSGi specification defines a special bundle, called the System Bundle, that represents the framework at run time and appears like any other bundle in the list of installed bundles. To make this notion even more intuitive, the Felix class implements the org.osgi.framework.Bundle interface, which is reiterated here:
| Code Block |
|---|
public interface Bundle
{
public BundleContext getBundleContext();
public long getBundleId();
public URL getEntry(String name);
public Enumeration getEntryPaths(String path);
public Enumeration findEntries(String path, String filePattern, boolean recurse);
public Dictionary getHeaders();
public Dictionary getHeaders(String locale);
public long getLastModified();
public String getLocation();
public URL getResource(String name);
public Enumeration getResources(String name) throws IOException;
public ServiceReference[] getRegisteredServices();
public ServiceReference[] getServicesInUse();
public int getState();
public String getSymbolicName();
public boolean hasPermission(Object obj);
public Class loadClass(String name) throws ClassNotFoundException;
public void start() throws BundleException;
public void stop() throws BundleException;
public void uninstall() throws BundleException;
public void update() throws BundleException;
public void update(InputStream is) throws BundleException;
}
|
When you instantiate the Felix class, the resulting object is actually the System Bundle and can be cast to the Bundle interface. The start() method is used to start the framework instance, while the stop() method is used to asynchronously stop the framework instance. The Felix class also includes the following two additional public methods:
| Code Block |
|---|
public class Felix extends AbstractBundle
{
public Felix(MutablePropertyResolver configMutable, List activatorList);
public void stopAndWait();
}
|
The first method is the constructor used to instantiate framework instances; the constructor accepts configuration properties and System Bundle activators, which are both described in more detail later. The stopAndWait() method is a synchronous version of the stop() method, used to stop the framework and block the calling thread until the framework is completely stopped.
| Anchor | ||||
|---|---|---|---|---|
|
Launching Felix
Launching Felix is fairly simple and involves only three steps:
- Defining some configuration properties.
- Creating an instance of
org.apache.felix.framework.Felixwith the configuration properties. - Invoking the
org.apache.felix.framework.Felix.start()method.
The only configuration properties that are actually required to The only configuration properties that are actually required to start Felix are ones that tell it where/how to locate the bundle cache profile directory where installed bundles will be cached. Felix' bundle cache implementation allows you to configure the location where bundles are cached using configuration properties. At a minimum, either a bundle cache profile name or directory must be specified; see the bundle cache document for more detailed information on configuring the bundle cache.
...
The standard Felix launcher is very simple and is not intended to solve every possible requirement; it is intended to work for most standard situations. Most special launching requirements should likely create their own be resolved by creating a custom launcher. This section describes how the standard launcher works. The following code represents the complete main() method of the standard launcher, each numbered comment will be described in more detail below:
| Code Block |
|---|
public static void main(String[] argv) throws Exception
{
// (1) Load system properties.
Main.loadSystemProperties();
// (2) Read configuration properties.
Properties configProps = Main.loadConfigProperties();
// (3) Copy framework properties from the system properties.
Main.copySystemProperties(configProps);
// (4) See if the profile name property was specified.
String profileName = configProps.getProperty(BundleCache.CACHE_PROFILE_PROP);
// (4) See if the profile directory property was specified.
String profileDirName = configProps.getProperty(BundleCache.CACHE_PROFILE_DIR_PROP);
// Print welcome banner.
System.out.println("\nWelcome to Felix.");
System.out.println("=================\n");
// (5) If no profile or profile directory is specified in the
// properties, then ask for a profile name.
if ((profileName == null) && (profileDirName == null))
{
System.out.print("Enter profile name: ");
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
try
{
profileName = in.readLine();
}
catch (IOException ex)
{
System.err.println("Could not read input.");
System.exit(-1);
}
System.out.println("");
if (profileName.length() != 0)
{
configProps.setProperty(BundleCache.CACHE_PROFILE_PROP, profileName);
}
}
// (6) A profile directory or name must be specified.
if ((profileDirName == null) && (profileName.length() == 0))
{
System.err.println("You must specify a profile name or directory.");
System.exit(-1);
}
try
{
// (7) Now create an instance of the framework.
m_felix = new Felix(
new MutablePropertyResolverImpl(
new StringMap(configProps, false)),
null);
m_felix.start();
}
catch (Exception ex)
{
System.err.println("Could not create framework: " + ex);
ex.printStackTrace();
System.exit(-1);
}
}
|
...
- Load any system properties specified in the
system.propertiesfile; this file is typically located in theconf/directory of the Felix installation directory, but it can be specified directly using thefelix.system.propertiessystem property. This file is not needed to launch Felix and is provided merely for convenience when system properties must be specified. The file is a standard Java properties file, but it also supports property substitution using${<property-name} syntax. Property substitution can be nested; only system properties will be used for substitution. - Load any configuration properties specified in the
config.propertiesfile; this file is typically located in theconf/directory of the Felix installation directory, but it can be specified directly using thefelix.config.propertiessystem property. This file is used to configure the Felix instance created by the launcher. The file is a standard Java properties file, but it also supports property substitution using "${<property-name}" syntax. Property substitution can be nested; configuration and system properties will be used for substitution with configuration properties having precedence. - For convenience, any configuration properties that are set as system properties will be copied into the set of configuration properties to provide an easy way to add to or override configuration properties specified in the
config.propertiesfile. - Try to load the profile name or profile directory configuration properties. At least one of these must be specified so that the bundle cache knows where to save installed bundles.
- If either the profile name or profile directory configuration property has not been specified, then ask the user to specify a profile name and add it to the current set of configuration properties.
- Error if there is no profile name or profile directory.
- Create the Felix instance , passing in the configuration properties , and then call
start().
The framework is not active until the start() method is called. If no shell bundles are specified in the config.properties file or if there is difficulty locating the shell bundles that are specified, then it will appear as if the framework is hung, but it is actually running without any way to interact with it since the shell bundles provide the only means of interaction.
...
This section creates a bare-bones launcher to demonstrate the minimum requirements for creating an interactive launcher for the Felix framework. This example uses the standard Felix shell bundles for interactivity, but any other bundles could be used instead. For example, the shell service and telnet bundles could be used to lauch launch Felix and make it remotely accessible.
...
| No Format |
|---|
launcher/
lib/
org.apache.felix.framework-0.8.0-SNAPSHOT.jar
org.osgi.core-0.8.0-SNAPSHOT1.0.0.jar
bundle/
org.apache.felix.shell-1.0.8.0-SNAPSHOT.jar
org.apache.felix.shell.tui-1.0.8.0-SNAPSHOT.jar
src/
example/
Main.java
|
The lib/ directory contains the JAR files for the framework as well as the OSGi framework JAR file, which also contains the OSGi core interfaces. The bundle/ directory contains the shell service and textual shell interface bundles that will be used for interacting with the framework instance. Note: If you do not launch Felix with interactive bundles, it will appear as if the framework instance is hung, but it is actually just sitting there waiting for someone to tell it to do something. The src/example/ directory contains the following Main.java file, which is a very simplistic Felix launcher.
| Code Block |
|---|
package example;
import java.util.Map;
import org.osgi.framework.Constants;
import org.apache.felix.framework.Felix;
import org.apache.felix.framework.cache.BundleCache;
import org.apache.felix.framework.util.MutablePropertyResolverImpl;
import org.apache.felix.framework.util.StringMap;
import org.apache.felix.framework.util.FelixConstants;
public class Main
{
private static Felix m_felix = null;
public static void main(String[] argv) throws Exception
{
// Print welcome banner.
System.out.println("\nWelcome to Felix.");
System.out.println("=================\n");
Map configMap = new StringMap(false);
configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES,
"org.osgi.framework; version=1.3.0," +
"org.osgi.service.packageadmin; version=1.2.0," +
"org.osgi.service.startlevel; version=1.0.0," +
"org.osgi.service.url; version=1.0.0");
configMap.put(FelixConstants.AUTO_START_PROP + ".1",
"file:bundle/org.apache.felix.shell-1.0.8.0-SNAPSHOT.jar " +
"file:bundle/org.apache.felix.shell.tui-1.0.8.0-SNAPSHOT.jar");
configMap.put(BundleCache.CACHE_PROFILE_DIR_PROP, "cache");
try
{
// Now create an instance of the framework.
m_felix = new Felix(
new MutablePropertyResolverImpl(configMap),
null);
m_felix.start();
}
catch (Exception ex)
{
System.err.println("Could not create framework: " + ex);
ex.printStackTrace();
System.exit(-1);
}
}
}
|
...
| Code Block |
|---|
configMap.put(FelixConstants.AUTO_START_PROP + ".1",
"file:bundle/org.apache.felix.shell-1.0.8.0-SNAPSHOT.jar " +
"file:bundle/org.apache.felix.shell.tui-1.0.8.0-SNAPSHOT.jar");
|
This sets the FelixConstants.AUTO_START_PROP configuration property (string value "felix.auto.start"), which is a space-delimited list of bundle URLs that the framework will automatically install and start when the framework starts. However, this property key cannot be used as is; it must be appended with a "." and then a number, where the number represents the start level for the bundle when it is installed. In this particular example, ".1" is appended to the property name, thus the two bundles will be installed into start level one. This example uses relative file: URLs, which will load the bundles from the bundle/ directory assuming that the launcher is started from the root directory of the launcher project. It is also possible to specify absolute URLs or remote URLs.
...
This sets the last configuration property, BundleCache.CACHE_PROFILE_DIR_PROP (string value "felix.cache.profiledir"), which is a string that specifies the precise directory to be used as the bundle cache profile directory; the Felix bundle cache supports other properties to configure its behavior, but those are not covered here. In this example, the bundle cache profile directory is specified as a relative directory called "cache". Assuming that the launcher is executed from the root directory of the launcher project, then the bundle cache profile directory will be created in the root directory of the project.
| Code Block |
|---|
m_felix = new Felix( m_felix = new FelixMutablePropertyResolverImpl(configMap), null); m_felix.start(); |
The last steps create the framework instance and start it. The configuration property map is converted to an instance of a PropertyResolver before being passed into the Felix constructor.start() method.
The following command compiles the launcher when run from the root directory of the launcher project:
| No Format |
|---|
javac -d . -classpath lib/org.apache.felix.framework-0.8.0-SNAPSHOT.jar:lib/org.osgi.core-0.8.0-SNAPSHOT1.0.0.jar src/example/Main.java |
...
| No Format |
|---|
java -cp .:lib/org.apache.felix.framework-0.8.0-SNAPSHOT.jar:lib/org.osgi.core-0.8.0-SNAPSHOT1.0.0.jar example.Main |
After executing this command, a cache/ directory is created that contains the installed bundles, which were installed from the bundle/ directory.
...
In the section on launching Felix above, the start() method was used to start a Felix framework instance executing. The start() method Felix constructor accepts two arguments, the first being the configuration properties for the framework, the second being a list of bundle activator instances. These bundle activator instances provide the foundation for how the host application interacts a convenient way for host applications to interact with the Felix framework.
Each bundle activator instance passed into the start() method constructor effectively becomes part of the System Bundle. This means that the start()/stop() method of each bundle activator instance in the passed in list gets invoked when the System Bundle's activator start()/stop() method gets invoked. Consequently, each bundle activator instance will be passed given the system bundle's BundleContext object so that they can interact with the framework externally. While it is possible to get the System Bundle's BundleContext object directly by calling Felix.getBundleContext(), this is generally not as convenient since it requires that you monitor when the System Bundle starts and/or stops. Consider following snippet of a bundle activator:
| Code Block |
|---|
public class HostActivator implements BundleActivator
{
private BundleContext m_context = null;
public void start(BundleContext context)
{
m_context = null; = context;
}
public void startstop(BundleContext context)
{
m_context = contextnull;
}
public voidBundle[] stopgetBundles(BundleContext context)
{
if (m_context != null;)
}
{
public BundleContext getContextreturn m_context.getBundles();
{ }
return m_contextnull;
}
}
|
Given the above bundle activator, it is now possible to embed Felix into a host application and interact with it as the following snippet illustrates:
| Code Block |
|---|
public class HostApplication
{
private HostActivator m_activator = null;
private Felix m_felix = null;
public HostApplication()
{
// Create a case-insensitive configuration property map.
Map configMap = new StringMap(false);
// Configure the Felix instance to be embedded.
configMap.put(FelixConstants.EMBEDDED_EXECUTION_PROP, "true");
// Add core OSGi packages to be exported from the class path
// via the system bundle.
configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES,
"org.osgi.framework; version=1.3.0," +
"org.osgi.service.packageadmin; version=1.2.0," +
"org.osgi.service.startlevel; version=1.0.0," +
"org.osgi.service.url; version=1.0.0");
// Explicitly specify the directory to use for caching bundles.
configMap.put(BundleCache.CACHE_PROFILE_DIR_PROP, "cache");
try
{
// Create host activator;
m_activator = new HostActivator();
List list = new ArrayList();
list.add(m_activator);
// Now create an instance of the framework with
// our configconfiguration properties and activator.
m_felix = new Felix(
new MutablePropertyResolverImpl(configMap),
list);
// Now start Felix instance.
m_felix.start();
}
catch (Exception ex)
{
System.err.println("Could not create framework: " + ex);
ex.printStackTrace();
}
}
public Bundle[] getInstalledBundles()
{
// Use the system bundle activator to gain external
// access to the set of installed bundles.
return m_activator.getContext().getBundles();
}
public void shutdownApplication()
{
// Shut down the felix framework when stopping the
// host application.
m_felix.shutdown();
}
}
|
...
| Code Block |
|---|
package host.core; import java.util.List; import java.util.ArrayList; import java.util.Map; import java.util.HashMap; import host.service.lookup.Lookup; import org.apache.felix.framework.Felix; import org.apache.felix.framework.util.FelixConstants; import org.apache.felix.framework.util.StringMap; import org.apache.felix.framework.util.MutablePropertyResolverImpl; import org.apache.felix.framework.cache.BundleCache; public class HostApplication { private HostActivator m_activator = null; private Felix m_felix = null; private Map m_lookupMap = new HashMap(); public HostApplication() { // Initialize the map for the property lookup service. m_lookupMap.put("name1", "value1"); m_lookupMap.put("name2", "value2"); m_lookupMap.put("name3", "value3"); m_lookupMap.put("name4", "value4"); // Create a case-insensitive configuration property map. Map configMap = new StringMap(false); // Configure the Felix instance to be embedded. configMap.put(FelixConstants.EMBEDDED_EXECUTION_PROP, "true"); // Add the host provided service interface package and the core OSGi // packages to be exported from the class path via the system bundle. configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES, "org.osgi.framework; version=1.3.0," + "org.osgi.service.packageadmin; version=1.2.0," + "org.osgi.service.startlevel; version=1.0.0," + "org.osgi.service.url; version=1.0.0," + "host.service.lookup; version=1.0.0"); // Explicitly specify the directory to use for caching bundles. configMap.put(BundleCache.CACHE_PROFILE_DIR_PROP, "cache"); try { // Create host activator; m_activator = new HostActivator(m_lookupMap); List list = new ArrayList(); list.add(m_activator); // Now create an instance of the framework with // our configconfiguration properties and activator. m_felix = new Felix( new MutablePropertyResolverImpl(configMap), list); // Now start Felix instance. m_felix.start(); } catch (Exception ex) { System.err.println("Could not create framework: " + ex); ex.printStackTrace(); } } public void shutdownApplication() { // Shut down the felix framework when stopping the // host application. m_felix.shutdown(); } } |
...
| Code Block |
|---|
package host.core;
import java.util.Map;
import host.service.command.Command;
import org.apache.felix.framework.Felix;
import org.apache.felix.framework.util.FelixConstants;
import org.apache.felix.framework.util.StringMap;
import org.apache.felix.framework.util.MutablePropertyResolverImpl;
import org.apache.felix.framework.cache.BundleCache;
import org.osgi.util.tracker.ServiceTracker;
public class HostApplication
{
private HostActivator m_activator = null;
private Felix m_felix = null;
private ServiceTracker m_tracker = null;
public HostApplication()
{
// Create a case-insensitive configuration property map.
Map configMap = new StringMap(false);
// Configure the Felix instance to be embedded.
configMap.put(FelixConstants.EMBEDDED_EXECUTION_PROP, "true");
// Add the bundle provided service interface package and the core OSGi
// packages to be exported from the class path via the system bundle.
configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES,
"org.osgi.framework; version=1.3.0," +
"org.osgi.service.packageadmin; version=1.2.0," +
"org.osgi.service.startlevel; version=1.0.0," +
"org.osgi.service.url; version=1.0.0," +
"host.service.command; version=1.0.0");
// Explicitly specify the directory to use for caching bundles.
configMap.put(BundleCache.CACHE_PROFILE_DIR_PROP, "cache");
try
{
// Create host activator;
m_activator = new HostActivator(m_lookupMap);
List list = new ArrayList();
list.add(m_activator);
// Now create an instance of the framework with
// our configconfiguration properties and activator.
m_felix = new Felix(
new MutablePropertyResolverImpl(configMap),
list);
// Now start Felix instance.
m_felix.start();
}
catch (Exception ex)
{
System.err.println("Could not create framework: " + ex);
ex.printStackTrace();
}
m_tracker = new ServiceTracker(
m_activator.getContext(), Command.class.getName(), null);
m_tracker.open();
}
public boolean execute(String name, String commandline)
{
// See if any of the currently tracked command services
// match the specified command name, if so then execute it.
Object[] services = m_tracker.getServices();
for (int i = 0; (services != null) && (i < services.length); i++)
{
try
{
if (((Command) services[i]).getName().equals(name))
{
return ((Command) services[i]).execute(commandline);
}
}
catch (Exception ex)
{
// Since the services returned by the tracker could become
// invalid at any moment, we will catch all exceptions, log
// a message, and then ignore faulty services.
System.err.println(ex);
}
}
return false;
}
public void shutdownApplication()
{
// Shut down the felix framework when stopping the
// host application.
m_felix.shutdown();
}
}
|
...