Apache Felix Framework Launching and Embedding

Wiki Markup_\[This document describes framework launching introduced in Felix Framework 2.0.0 and is incompatible with older versions of the Felix framework.\]_and continuing with the latest releases; it is incompatible with older versions of the Felix framework.]

• Introduction
• OSGi Launching and Embedding
• Introduction
• API Overview
  • Creating and Configuring the Framework Instance
  • Starting the Framework Instance
  • Stopping the Framework Instance
• Launching Felix
  • Standard Felix Launcher
  • Custom Felix Launcher
• Embedding Felix
  • Host/Felix Interaction
  • Providing Host Application Services
  • Using Services Provided by Bundles
    • Using Bundle Services via Reflection
    • Other Approaches
• Caveat
• Feedback

...

Introduction

The Apache Felix framework Framework is intended to be easily launchable and embeddable. For example, the Felix framework implementation avoids the use of system properties for configuration, since these are globals and can cause interference if multiple framework instances are created in the same VM. Felix The framework also tries 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 possiblethe framework in a variety of scenarios; 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 overviewan overview of the standard OSGi launching and embedding API for frameworks, while the remainder of the document is divided into two sections, one focusing on how to launch Felix and one focusing on how to embed Felix into a host application.

OSGi Launching and Embedding API Overview

The Felix framework is implemented by the org.apache.felix.framework.Felix class or just Felix for short. As part of the ongoing R4.2 OSGi specification process, there is a movement to standardize the API for launching and embedding API of the OSGi framework implementationshas been standardized. The approach is to have the framework implement the org.osgi.framework.launch.Framework interface, which extends the org.osgi.framework.Bundle interface. These interfaces provide the necessary means to launch and manage framework instances. The Bundle interface is defined as:

public interface Bundle
{
    BundleContext getBundleContext();
    long getBundleId();
    URL getEntry(String name);
    Enumeration getEntryPaths(String path);
    Enumeration findEntries(String path, String filePattern, boolean recurse);
    Dictionary getHeaders();
    Dictionary getHeaders(String locale);
    long getLastModified();
    String getLocation();
    URL getResource(String name);
    Enumeration getResources(String name) throws IOException;
    ServiceReference[] getRegisteredServices();
    ServiceReference[] getServicesInUse();
    int getState();
    String getSymbolicName();
    Version getVersion();
    boolean hasPermission(Object obj);
    Class loadClass(String name) throws ClassNotFoundException;
    void start() throws BundleException;
    void stop() throws BundleException;
    void uninstall() throws BundleException;
    void update() throws BundleException;
    void update(InputStream is) throws BundleException;
}

...

public interface Framework extends Bundle
{
    void init();
    FrameworkEvent waitForStop(long timeout);
}

An additional requirement for framework implementations not captured in the interface definitions is that they must implement a public constructor that accepts a Map, which is used to pass in configuration properties. When you instantiate the Felix class, the resulting object is the actual System Bundle that bundles inside the framework will see if they get bundle 0, which is the System Bundle as defined by the OSGi specification.

To actually construct a framework instance, the R4.2 specification defines the FrameworkFactory interface:

public interface FrameworkFactory
{
    Framework newFramework(Map config);
}

The framework factory can be used to create configured framework instances. It is obtained following the standard META-INF/services approach.

Creating and Configuring the Framework Instance

To create You use the framework factory to construct and configure a framework instance , simply instantiate (or by directly instantiating the Felix class. A newly created framework instance is in the Bundle.INSTALLED state. You configure the instance by passing the constructor a Map containing its configurations ). The configuration map may contain any of the framework configuration properties listed in the Apache Felix Framework Configuration Properties document, not the launcher configuration properties. The configuration map may contain the following OSGi standard properties:

• org.osgi.framework.system.packages - specifies a list of packages the system bundle should export from the environment; if this is not set, then the framework uses a reasonable default fault.
• org.osgi.framework.system.packages.extra - specifies a list of additional packages the system bundle should export from the environment that are appended to the packages specified in org.osgi.framework.system.packages; there is no default value for this property.
• org.osgi.framework.bootdelegation - specifies a list of packages that should be made implicitly available to all bundles from the environment (i.e., no need to import them); there is no default value for this property and its use should be avoided.
• org.osgi.framework.storage - specifies the path to a directory, which will be created if it does not exist, to use for bundle cache storage; the default value for this property is "felix-cache" in the current working directory.
• org.osgi.framework.storage.clean - specifies whether the bundle cache should be flushed; the default value for this property is "none", but it can be changed to "onFirstInit" to flush the bundle cache when the framework is initialized.
• org.osgi.framework.startlevel.beginning - specifies the start level the framework enters upon startup; the default value for this property is 1.

Felix also has the following, non-standard configuration properties:

• felix.cache.rootdir - specifies which directory should be used to calculate absolute paths when relative paths are used for the org.osgi.framework.storage property; the default value for this property is the current working directory.
• felix.systembundle.activators - specifies a List of BundleActivator instances that are started/stopped when the System Bundle is started/stopped; the specified instances will receive the System Bundle's BundleContext when invoked.
• felix.log.logger - specifies an instance of org.apache.felix.framework.util.Logger that the framework uses as its default logger.
• felix.log.level - specifies an integer String whose value indicates the degree of logging reported by the framework; the default value is "1" and "0" turns off logging completely, otherwise log levels match those specified in the OSGi Log Service (i.e., 1 = error, 2 = warning, 3 = information, and 4 = debug).
• felix.startlevel.bundle - specifies the start level for newly installed bundles; the default value is 1.
• felix.bootdelegation.implicit - specifies whether or not the framework should try to guess when to boot delegate when external code tries to load classes or resources; the default value is "true".
• framework.service.urlhandlers - specifies whether or not to activate the URL Handlers service for the framework instance; the default value is "true", which results in the URL.setURLStreamHandlerFactory() and URLConnection.setContentHandlerFactory() being called.

The configuration map passed into the constructor is copied and the keys are treated as case insensitive. You are not able to change the framework's configuration after construction. If you need a different configuration, you must create a new framework instance.

...

is copied and the keys are treated as case insensitive. You are not able to change the framework's configuration after construction. If you need a different configuration, you must create a new framework instance.

Starting the Framework Instance

The start() method is used to start the framework instance. If the init() method was not invoked prior to calling start(), then it is invoked by start(). The two methods result in two different framework state transitions:

• init() results in the framework instance in the Bundle.STARTING state.
• start() results in the framework instance in the Bundle.ACTIVE state.

The init() method is necessary since the framework does not have a BundleContext when it is first created, so a transition to the Bundle.STARTING state is required to acquire its context (via Bundle.getBundleContext()) for performing various tasks, such as installing bundles. Note that the Felix framework also provides the felix.systembundle.activators property that serves a similar purpose, but is not standard. After the init() method completes, the follow actions have been performed:

• Event handling is enabled.
• The security manager is installed if it is enabled.
• The framework is set to start level 0.
• All bundles in the bundle caches are reified and their state is set to Bundle.INSTALLED.
• The framework gets a valid BundleContext.
• All framework-provided services are made available (e.g., PackageAdmin, StartLevel, etc.).
• The framework enters the Bundle.STARTING state.

A call to start() is necessary to start the framework instance, if the init() method is invoked manually. Invoking init() or start() on an already started framework as no effect.

Stopping the Framework Instance

To stop the framework instance, invoke the stop() method, which will asynchronously stop the framework. To know when the framework has finished its shutdown sequence, use the waitForStop() method to wait until it is complete. A stopped framework will be in the Bundle.RESOLVED state. It is possible to restart the framework, using the normal combination of init()/start() methods as previously described.

Launching a Framework

Launching a framework is fairly simple and involves only four steps:

1. Define some configuration properties.
2. Obtain framework factory.
3. Use factory to create framework with the configuration properties.
4. Invoke the Framework.start() method.

In reality, the first step is optional, since all properties will have reasonable defaults, but if you are creating a launcher you will generally want to more than that, such as automatically installing and starting bundles when you start the framework instance. The default Felix launcher defines reusable functionality to automatically install and/or start bundles upon framework startup; see the usage document for more information on configuring the Felix framework and on the various configuration properties.

The remainder of this section describes how the standard Felix launcher works as well as how to create a custom launcher.

Standard Felix Framework Launcher

The standard Felix framework 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 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:

public static void main(String[] args) throws Exception
{
    // (1) Check for command line arguments and verify usage.
    String bundleDir = null;
    String cacheDir = null;
    boolean expectBundleDir = false;
    for (int i = 0; i < args.length; i++)
    {
        if (args[i].equals(BUNDLE_DIR_SWITCH))
        {
            expectBundleDir = true;
        }
        else if (expectBundleDir)
        {
            bundleDir = args[i];
            expectBundleDir = false;
        }
        else
        {
            cacheDir = args[i];
        }
    }

    if ((args.length > 3) || (expectBundleDir && bundleDir == null))
    {
        System.out.println("Usage: [-b <bundle-deploy-dir>] [<bundle-cache-dir>]");
        System.exit(0);
    }

    // (2) Load system properties.
    Main.loadSystemProperties();

    // (3) Read configuration properties.
    Properties configProps = Main.loadConfigProperties();
    if (configProps == null)
    {
        System.err.println("No " + CONFIG_PROPERTIES_FILE_VALUE + " found.");
        configProps = new Properties();
    }

    // (4) Copy framework properties from the system properties.
    Main.copySystemProperties(configProps);
        
    // (5) Use the specified auto-deploy directory over default.
    if (bundleDir != null)
    {
        configProps.setProperty(AutoProcessor.AUTO_DEPLOY_DIR_PROPERY, bundleDir);
    }

    // (6) Use the specified bundle cache directory over default.
    if (cacheDir != null)
    {
        configProps.setProperty(Constants.FRAMEWORK_STORAGE, cacheDir);
    }

    // (7) Add a shutdown hook to clean stop the framework.
    String enableHook = configProps.getProperty(SHUTDOWN_HOOK_PROP);
    if ((enableHook == null) || !enableHook.equalsIgnoreCase("false"))
    {
        Runtime.getRuntime().addShutdownHook(new Thread("Felix Shutdown Hook") 

...

Starting the Framework Instance

The start() method is used to start the framework instance. If the init() method was not invoked prior to calling start(), then it is invoked by start(). The two methods result in two different framework state transitions:

• init() results in the framework instance in the Bundle.STARTING state.
• start() results in the framework instance in the Bundle.ACTIVE state.

The init() method is necessary since the framework does not have a BundleContext when it is first created, so a transition to the Bundle.STARTING state is required to acquire its context (via Bundle.getBundleContext()) for performing various tasks, such as installing bundles. Note that Felix also provides the felix.systembundle.activators property that serves a similar purpose. After the init() method completes, the follow actions have been performed:

• Event handling is enabled.
• The security manager is installed if it is enabled.
• The framework is set to start level 0.
• All bundles in the bundle caches are reified and their state is set to Bundle.INSTALLED.
• The framework gets a valid BundleContext.
• All framework-provided services are made available (e.g., PackageAdmin, StartLevel, etc.).
• The framework enters the Bundle.STARTING state.

A call to start() is necessary to start the framework instance, if the init() method is invoked manually. Invoking init() or start() on an already started framework as no effect.

...

Stopping the Framework Instance

To stop the framework instance, invoke the stop() method, which will asynchronously stop the framework. To know when the framework has finished its shutdown sequence, use the waitForStop() method to wait until it is complete. A stopped framework will be in the Bundle.RESOLVED state. It is possible to restart the framework, using the normal combination of init()/start() methods as previously described.

...

Launching Felix

Launching Felix is fairly simple and involves only three steps:

1. Define some configuration properties.
2. Create an instance of org.apache.felix.framework.Felix with the configuration properties.
3. Invoke the org.apache.felix.framework.Felix.start() method.

In reality, the first step is optional, since all properties will have reasonable defaults, but if you are creating a launcher you will generally want to more than that, such as automatically installing and starting bundles when you start the framework instance. The default Felix launcher defines reusable functionality to automatically install and/or start bundles upon framework startup; see the usage document for more information on configuring Felix and on the various configuration properties.

The remainder of this section describes how the standard Felix launcher works as well as how to create a custom launcher for Felix.

...

Standard Felix Launcher

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 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:

public static void main(String[] args) throws Exception
{
    // (1) Check for command line arguments and verify usage.
    String bundleDir = null;
    String cacheDir = null;
    boolean expectBundleDir = false;
    for (int i = 0; i < args.length; i++)
    {
        if (args[i].equals(BUNDLE_DIR_SWITCH))
        {
            expectBundleDir = true;
        }
        else if (expectBundleDir)
        {
            bundleDirpublic = args[i];void run()
            expectBundleDir = false;{
        }
        elsetry
        {
        {
    cacheDir = args[i];
        }
    }
    if ((args.length > 3) || (expectBundleDir && bundleDir == null))
m_fwk != null)
         {
        System.out.println("Usage: [-b <bundle-deploy-dir>] [<bundle-cache-dir>]"); {
        System.exit(0);
    }

    // (2) Load system properties.
    Mainm_fwk.loadSystemPropertiesstop();

      // (3) Read configuration properties.
    Properties configProps = Main.loadConfigProperties();
    if (configProps == null) m_fwk.waitForStop(0);
    {
         System.err.println("No " + CONFIG_PROPERTIES_FILE_VALUE + " found.");       }
        configProps  = new Properties();
    }

     // (4) Copy framework properties from the system properties.
   catch Main.copySystemProperties(configProps);
(Exception ex)
         
    // (5) Use the{
 specified auto-deploy directory over default.
    if (bundleDir != null)
    {
    System.err.println("Error stopping framework:  configProps.setProperty(AutoProcessor.AUTO_DEPLOY_DIR_PROPERY, bundleDir" + ex);
    }

    // (6) Use the specified bundle cache directory over}
 default.
    if (cacheDir != null)
    {}
        configProps.setProperty(Constants.FRAMEWORK_STORAGE, cacheDir});
    }

    try
    {
        // (78) AddCreate aan shutdowninstance hookand toinitialize clean stop the framework.
        FrameworkFactory factory = getFrameworkFactory();
    String enableHook    m_fwk = configPropsfactory.getProperty(SHUTDOWN_HOOK_PROPnewFramework(configProps);
    if ((enableHook == null) || !enableHook.equalsIgnoreCase("false")) m_fwk.init();
    {
        Runtime.getRuntime().addShutdownHook(new Thread() {
      // (9) Use the system bundle context to process the auto-deploy
      public void run()
    // and auto-install/auto-start properties.
         {AutoProcessor.process(configProps, m_fwk.getBundleContext());
                try// (10) Start the framework.
        m_fwk.start();
        {
             // (11) Wait for framework to stop to exit the VM.
       if (m_fwk != null)
.waitForStop(0);
        System.exit(0);
    }
    catch (Exception ex)
    {
        System.err.println("Could not create framework: " + ex);
          m_fwk.stopex.printStackTrace();
                        m_fwk.waitForStop(0);
                    }
                }
                catch (Exception ex)
                {
                    System.err.println("Error stopping framework: " + ex);
                }
            }
        });
    }

    // Print welcome banner.
    System.out.println("\nWelcome to Felix");
    System.out.println("================\n");

    try
    {
        // (8) Create an instance and initialize the framework.
        FrameworkFactory factory = getFrameworkFactory();
        m_fwk = factory.newFramework(configProps);
        m_fwk.init();
        // (9) Use the system bundle context to process the auto-deploy
        // and auto-install/auto-start properties.
        AutoProcessor.process(configProps, m_fwk.getBundleContext());
        // (10) Start the framework.
        m_fwk.start();
        // (11) Wait for framework to stop to exit the VM.
        m_fwk.waitForStop(0);
        System.exit(0);
    }
    catch (Exception ex)
    {
        System.err.println("Could not create framework: " + ex);
        ex.printStackTrace();
        System.exit(-1);
    }
}

The general steps of the standard launcher are quite straightforward:

1. The launcher supports setting the auto-deploy directory (with the -b switch) and setting the bundle cache path with a single argument, so check for this and issue a usage message it there are more than one arguments.
2. Load any system properties specified in the system.properties file; this file is typically located in the conf/ directory of the Felix installation directory, but it can be specified directly using the felix.system.properties system 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 ${<property-name} syntax. Property substitution can be nested; only system properties will be used for substitution.
3. Load any configuration properties specified in the config.properties file; this file is typically located in the conf/ directory of the Felix installation directory, but it can be specified directly using the felix.config.properties system property. This file is used to configure the Felix instance created by the launcher. The file is a standard Java properties file, but it also supports property substitution using "${<property-name}" syntax. Property substitution can be nested; configuration and system properties will be used for substitution with configuration properties having precedence.
4. For convenience, any configuration properties that are set as system properties are copied into the set of configuration properties. This provide an easy way to add to or override configuration properties specified in the config.properties file, since the Felix instance will never look at system properties for configuration.
5. If the -b switch was used to specify an auto-deploy directory, then use that to set the value of felix.auto.deploy.dir.
6. If a single command-line argument is specified, then use that to set the value of org.osgi.framework.storage; relative paths are relative to the current directory unless the felix.cache.rootdir property is set.
7. Create a framework instance using the FrameworkFactory passing in the configuration properties, then initialize the factory instance.
8. Use org.apache.felix.main.AutoProcessor, which will automatically deploy any bundles in the auto-deploy directory as well as bundles specified in the felix.auto.install and felix.auto.start configuration properties during framework startup to automatically install and/or start bundles; see the usage document for more information configuration properties and bundle auto-deploy.
9. Invoke waitForStop() to wait for the framework to stop to force the VM to exit; this is necessary because the framework never calls System.exit() and some libraries (e.g., Swing) create threads that will not allow the VM to exit.

The framework is not active until the start() method is called. If no shell bundles are installed and started or if there is difficulty locating the shell bundles specified in the auto-start property, 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.

...

System.exit(0);
    }
}

The general steps of the standard launcher are quite straightforward:

1. The launcher supports setting the auto-deploy directory (with the -b switch) and setting the bundle cache path with a single argument, so check for this and issue a usage message it there are more than one arguments.
2. Load any system properties specified in the system.properties file; this file is typically located in the conf/ directory of the Felix installation directory, but it can be specified directly using the felix.system.properties system 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 ${<property-name} syntax. Property substitution can be nested; only system properties will be used for substitution.
3. Load any configuration properties specified in the config.properties file; this file is typically located in the conf/ directory of the Felix installation directory, but it can be specified directly using the felix.config.properties system property. This file is used to configure the framework instance created by the launcher. The file is a standard Java properties file, but it also supports property substitution using "${<property-name>}" syntax. Property substitution can be nested; configuration and system properties will be used for substitution with configuration properties having precedence.
4. For convenience, any configuration properties that are set as system properties are copied into the set of configuration properties. This provide an easy way to add to or override configuration properties specified in the config.properties file, since the Felix instance will never look at system properties for configuration.
5. If the -b switch was used to specify an auto-deploy directory, then use that to set the value of felix.auto.deploy.dir.
6. If a single command-line argument is specified, then use that to set the value of org.osgi.framework.storage; relative paths are relative to the current directory unless the felix.cache.rootdir property is set.
7. Add a shutdown hook to cleanly stop the framework, unless the hook is disabled.
8. Create a framework instance using the FrameworkFactory passing in the configuration properties, then initialize the factory instance; see the custom launcher example below to see how the META-INF/services FrameworkFactory is obtained.
9. Use org.apache.felix.main.AutoProcessor, which will automatically deploy any bundles in the auto-deploy directory as well as bundles specified in the felix.auto.install and felix.auto.start configuration properties during framework startup to automatically install and/or start bundles; see the usage document for more information configuration properties and bundle auto-deploy.
10. Invoke waitForStop() to wait for the framework to stop to force the VM to exit; this is necessary because the framework never calls System.exit() and some libraries (e.g., Swing) create threads that will not allow the VM to exit.

The framework is not active until the start() method is called. If no shell bundles are installed and started or if there is difficulty locating the shell bundles specified in the auto-start property, 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.

Custom Framework Launcher

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 Gogo shell bundles for interactivity, but any other bundles could be used instead. This example launcher project has the following directory structure:

launcher/
   lib/
      org.apache.felix.main-3.0.0.jar
   bundle/
      org.apache.felix.gogo.command-0.6.0.jar
      org.apache.felix.gogo.runtime-0.6.0.jar
      org.apache.felix.gogo.shell-0.6.0.jar
   src/
      example/
         Main.java

The lib/ directory contains Felix' main JAR file, which also contains the OSGi core interfaces. The main JAR file is used so that we can reuse the default launcher's auto-install/auto-start configuration property handling; if these capabilities are not needed, then it would be possible to use the framework JAR file instead of the main JAR file. 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 the framework 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 framework launcher.

package example;

import java.io.*;
import org.osgi.framework.launch.*;
import org.apache.felix.main.AutoProcessor;

public class Main
{
    private static Framework m_fwk = null;

    public static void main(String[] argv) throws Exception
    {
        // Print welcome banner.
        System.out.println("\nWelcome to My Launcher");
        System.out.println("======================\n");

        try
        {
            m_fwk = getFrameworkFactory().newFramework(null);
            m_fwk.init();
            AutoProcessor.process(null, m_fwk.getBundleContext());
            m_fwk.start();
            m_fwk.waitForStop(0);
            System.exit(0);
        }
        catch (Exception ex)
        {
            System.err.println("Could not create framework: " + ex);
            ex.printStackTrace();
            System.exit(-1);
        }
    }

    private static FrameworkFactory getFrameworkFactory() throws Exception
    {
        java.net.URL url = Main.class.getClassLoader().getResource(
            "META-INF/services/org.osgi.framework.launch.FrameworkFactory");
        if (url != null)
        {
            BufferedReader br = new BufferedReader(new InputStreamReader(url.openStream())

...

Custom Felix Launcher

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 launch Felix and make it remotely accessible.

This example launcher project has the following directory structure:

launcher/
   lib/
      org.apache.felix.main-1.4.0.jar
   bundle/
      org.apache.felix.shell-1.0.2.jar
      org.apache.felix.shell.tui-1.0.2.jar
   src/
      example/
         Main.java

The lib/ directory contains Felix' main JAR file, which also contains the OSGi core interfaces. The main JAR file is used so that we can reuse the default launcher's auto-install/auto-start configuration property handling; if these capabilities are not needed, then it would be possible to use the framework JAR file instead of the main JAR file. 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.

package example;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.HashMap;
import org.osgi.framework.Constants;
import org.apache.felix.framework.Felix;
import org.apache.felix.framework.util.FelixConstants;
import org.apache.felix.main.AutoActivator;

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 HashMap();
        configMap.put(AutoActivator.AUTO_START_PROP + ".1",
            "file:bundle/org.apache.felix.shell-1.0.2.jar " +
            "file:bundle/org.apache.felix.shell.tui-1.0.2.jar");
        List list = new ArrayList();try
        list.add(new AutoActivator(configMap));
    {
         configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);

       for (String s try
        {
= br.readLine(); s != null; s = br.readLine())
             m_felix = new Felix(configMap);{
            m_felix.start();
        s =   m_felix.waitForStops.trim();
              System.exit(0);
      // Try }
to load first non-empty, non-commented line.
   catch (Exception ex)
        {
       if ((s.length() > 0) && System.err.println("Could not create framework: " + ex);
(s.charAt(0) != '#'))
                    ex.printStackTrace();{
            System.exit(-1);
         }
    }
}

This launcher has all information hard coded in it, unlike the default Felix launcher, which loads configuration properties from files and performs variable substitution. This simple launcher provides a good starting point if the features of the default launcher are not necessary. Since very few configuration properties are specified, the default values are used. In the case of the framework bundle cache, it will use "felix-cache" in the current directory.

By breaking down the above source code into small chunks, it is quite easy to see what is going on.

return (FrameworkFactory) Class.forName(s).newInstance();
                    }
                }
            }
            finally
        Map configMap = new HashMap();

This simply creates a map to hold configuration properties.

{
                if configMap.put(AutoActivator.AUTO_START_PROP + ".1",(br != null) br.close();
            "file:bundle/org.apache.felix.shell-1.0.2.jar " +
  }
        }

        throw new "file:bundle/org.apache.felix.shell.tui-1.0.2.jar");

This sets the AutoActivator.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.

Exception("Could not find framework factory.");
    }
}

This launcher relies on the default behavior of AutoProcessor to automatically deploy the shell bundles. This simple, generic launcher provides a good starting point if the default Felix launcher is not sufficient. Since very few configuration properties are specified, the default values are used. For the bundle auto-deploy directory, "bundle" in the current directory is used, while for the framework bundle cache, "felix-cache" in the current directory is used.

By breaking down the above source code into small chunks, it is quite easy to see what is going on.

        List listm_fwk = new ArrayList(getFrameworkFactory().newFramework(null);
        list.add(new AutoActivator(configMap));    m_fwk.init()

These steps get a the framework factory service and use it to create a framework instance with a default configuration. Once the framework instance is created, it is initialized with init().

        configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);
    AutoProcessor.process(null, m_fwk.getBundleContext());

The AutorProcessor will automatically deploy bundles in the auto-deploy directory and any referenced from the auto-install/start properties. Since we are using an empty configuration, the auto-deploy directory is the bundle directory in the current directory and there are no auto properties. Therefore, in this case, the shell bundles will be installedThis above creates a list to hold custom framework activators and adds an instance of org.apache.felix.main.AutoActivator to it, which will process the auto-install and auto-start configuration properties during framework startup. The list of activators is then added to the configuration map.

            m_felix = new Felix(configMapfwk.start();
            m_fwk.waitForStop(0);
            m_felixSystem.startexit(0);

These steps create the framework instance and start it. The configuration property map is passed into the Felix constructorfinal steps start the framework and cause the launching application thread to wait for the framework to stop and when it does the launching thread calls System.exit() to make sure the VM actually exits.

    private static FrameworkFactory getFrameworkFactory() throws Exception
    m_felix.waitForStop();{
            System.exit(0);
...
    }

This method retrieves the framework factory service by doing a META-INF/services resource lookup, which it can use to obtain the concrete class name for the factory. If you are using Java 6, then you can use the ServiceLoader API in the JRE to further simplify the factory service lookupThese final steps cause the launching application thread to wait for the framework to stop and when it does the launching thread calls System.exit() to make sure the VM actually exits.

The following command compiles the launcher when run from the root directory of the launcher project:

javac -d . -classpath lib/org.apache.felix.main-13.40.0.jar src/example/Main.java

...

java -cp .:lib/org.apache.felix.main-13.40.0.jar example.Main

After executing this command, a "felix-cache/" directory is created that contains the installed cached bundles, which were installed from the bundle/ directory.

Embedding the Felix Framework

Embedding the Felix framework into a host application is a simple way to provide a sophisticated extensibility mechanism (i.e., a plugin system) to the host application. Embedding the Felix framework is very similar to launching Felix it as described above, the main difference is that the host application typically wants to interact with the framework instance and/or installed bundles/services from the outside. This is fairly easy to achieve with Felix, but there are some subtle issues to understand. This section presents the mechanisms for embedding Felix into a host application and the issues in doing so.

...

In the section on launching Felix the framework above, the Felix class accepts a configuration property called felix.systembundle.activators, which is a list of bundle activator instances. These bundle activator instances provide a convenient way for host applications to interact with the Felix framework. The ability offered by these activators can also be accomplished by invoking

...

...

Each activator instance passed into the constructor effectively becomes part of the System Bundlesystem bundle. This means that the start()/stop() methods of each activator instance in the list gets invoked when the System Bundlesystem bundle's activator start()/stop() methods gets invoked, respectively. Each activator instance will be given the System Bundlesystem bundle's BundleContext object so that they can interact with the framework. Consider following snippet of a bundle activator:

...

Given the above bundle activator, it is now possible to embed the Felix framework into a host application and interact with it as the following snippet illustrates:

public class HostApplication
{
    private HostActivator m_activator = null;
    private Felix m_felix = null;

    public HostApplication()
    {
        // Create a configuration property map.
        Map configMapconfig = new HashMap();
        // Create host activator;
        m_activator = new HostActivator();
        List list = new ArrayList();
        list.add(m_activator);
        configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);

        try
        {
            // Now create an instance of the framework with
            // our configuration properties.
            m_felix = new Felix(configMapconfig);
            // 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.getBundles();
    }

    public void shutdownApplication()
    {
        // Shut down the felix framework when stopping the
        // host application.
        m_felix.stop();
        m_felix.waitForStop(0);
    }
}

Notice how the HostApplication.getInstalledBundles() method uses its activator instance to get access to the System Bundlesystem bundle's context in order to interact with the embedded Felix framework instance. This approach provides the foundation for all interaction between the host application and the embedded framework instance.

...

package host.service.lookup;

public classinterface Lookup
{
    public Object lookup(String name);
}

...

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.osgi.framework.Constants;

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 configuration property map.
        Map configMap = new HashMap();
        // Export the host provided service interface package.
        configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
            "host.service.lookup; version=1.0.0");
        // Create host activator;
        m_activator = new HostActivator(m_lookupMap);
        List list = new ArrayList();
        list.add(m_activator);
        configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);

        try
        {
            // Now create an instance of the framework with
            // our configuration properties.
            m_felix = new Felix(configMap);
            // 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.stop();
        m_felix.waitForStop(0);
    }
}

Rather than having the host application bundle activator register the service, it is also possible for the the host application to simply get the bundle context from the bundle activator and register the service directly, but the presented approach is perhaps a little cleaner since it allows the host application to register/unregister the service when the system bundle starts/stops.

...

package host.core;

import java.util.List;
import java.util.ArrayList;
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.cache.BundleCache;
import org.osgi.framework.Constants;
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 configuration property map.
        Map configMap = new HashMap();
        // Export the host provided service interface package.
        configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA,
            "host.service.command; version=1.0.0");
        // Create host activator;
        m_activator = new HostActivator();
        List list = new ArrayList();
        list.add(m_activator);
        configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);

        try
        {
            // Now create an instance of the framework with
            // our configuration properties.
            m_felix = new Felix(configMap);
            // 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.stop();
        m_felix.waitForStop(0);
    }
}

The above example is overly simplistic with respect to concurrency issues and error conditions, but it demonstrates the overall approach for using bundle-provided services from the host application.

...