...

Apache

...

Felix

...

Framework

...

Launching

...

and

...

Embedding

...

[This

...

document

...

describes

...

framework

...

launching

...

introduced

...

in

...

Felix

...

Framework 2.0.0

...

and continuing with the latest releases; it is incompatible with older versions of the Felix framework.]

• Introduction
• OSGi Launching and Embedding 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

Anchor
introduction introduction

Introduction

The Apache Felix 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. The framework also tries to multiplex singleton facilities, like the URL stream handler factory. The goal is to make it possible to use the 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 an 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

...

R4.2

...

OSGi

...

specification,

...

the

...

launching

...

and

...

embedding

...

API

...

of

...

the

...

OSGi

...

framework

...

has

...

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;
}
{code}

The {

The Framework interface is defined as:

{Framework}} interface is defined as:

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

To

...

actually

...

construct

...

a

...

framework

...

instance,

...

the

...

R4.2

...

specification

...

defines

...

the

...

FrameworkFactory

...

interface:

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

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

You use the framework factory to construct and configure a framework instance (or by directly instantiating the Felix class). 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 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:

}

h2. Creating and Configuring the Framework Instance

You use the framework factory to construct and configure a framework instance (or by directly instantiating the Felix class). 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 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.

{warning:title=WARNING}
Felix configuration properties have change considerably starting from {{1.4.0}}; if you are upgrading from an earlier version, the [usage document|Apache Felix Framework Usage Documentation#migrating] describes the configuration property changes.
{warning}

{anchor:starting-instance}

h2. 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, 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.

{anchor:stopping-instance}

h2. 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.

{anchor:launching}

h1. Launching a Framework

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

# Define some configuration properties.
# Obtain framework factory.
# Use factory to create framework with the configuration properties.
# 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|Apache Felix Framework Usage Documentation#configuring-felix] 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.

{anchor:standard-launcher}

h2. 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:

{code}
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") {
            public void run()
            {
                try
                {
                    if (m_fwk != null)
                    {
                        m_fwk.stop();
                        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(-10);
    }
}
{code}

The

...

general

...

steps

...

of

...

the

...

standard

...

launcher

...

are

...

quite

...

straightforward:

...

1. The

...

1. launcher

...

1. supports

...

1. setting

...

1. the

...

1. auto-deploy

...

1. directory

...

1. (with

...

1. the

...

1. -b

...

1. switch)

...

1. and

...

1. setting

...

1. the

...

1. bundle

...

1. cache

...

1. path

...

1. with

...

1. a

...

1. single

...

1. argument,

...

1. so

...

1. check

...

1. for

...

1. this

...

1. and

...

1. issue

...

1. a

...

1. usage

...

1. message

...

1. it

...

1. there

...

1. are

...

1. more

...

1. than

...

1. one

...

1. arguments.

...

2. Load

...

1. any

...

1. system

...

1. properties

...

1. specified

...

1. in

...

1. the

...

1. system.properties

...

1. file;

...

1. this

...

1. file

...

1. is

...

1. typically

...

1. located

...

1. in

...

1. the

...

1. conf/

...

1. directory

...

1. of

...

1. the

...

1. Felix

...

1. installation

...

1. directory,

...

1. but

...

1. it

...

1. can

...

1. be

...

1. specified

...

1. directly

...

1. using

...

1. the

...

1. felix.system.properties

...

1. system

...

1. property.

...

1. This

...

1. file

...

1. is

...

1. not

...

1. needed

...

1. to

...

1. launch

...

1. Felix

...

1. and

...

1. is

...

1. provided

...

1. merely

...

1. for

...

1. convenience

...

1. when

...

1. system

...

1. properties

...

1. must

...

1. be

...

1. specified.

...

1. The

...

1. file

...

1. is

...

1. a

...

1. standard

...

1. Java

...

1. properties

...

1. file,

...

1. but

...

1. it

...

1. also

...

1. supports

...

1. property

...

1. substitution

...

1. using

...

1. $

...

1. {<property-name}

...

1. syntax.

...

1. Property

...

1. substitution

...

1. can

...

1. be

...

1. nested;

...

1. only

...

1. system

...

1. properties

...

1. will

...

1. be

...

1. used

...

1. for

...

1. substitution.

...

2. Load

...

1. any

...

1. configuration

...

1. properties

...

1. specified

...

1. in

...

1. the

...

1. config.properties

...

1. file;

...

1. this

...

1. file

...

1. is

...

1. typically

...

1. located

...

1. in

...

1. the

...

1. conf/

...

1. directory

...

1. of

...

1. the

...

1. Felix

...

1. installation

...

1. directory,

...

1. but

...

1. it

...

1. can

...

1. be

...

1. specified

...

1. directly

...

1. using

...

1. the

...

1. felix.config.properties

...

1. system

...

1. property.

...

1. This

...

1. file

...

1. is

...

1. used

...

1. to

...

1. configure

...

1. the

...

1. framework instance

...

1. created

...

1. by

...

1. the

...

1. launcher.

...

1. The

...

1. file

...

1. is

...

1. a

...

1. standard

...

1. Java

...

1. properties

...

1. file,

...

1. but

...

1. it

...

1. also

...

1. supports

...

1. property

...

1. substitution

...

1. using

...

1. "

...

1. $

...

1. {<property-

...

1. name>}

...

1. "

...

1. syntax.

...

1. Property

...

1. substitution

...

1. can

...

1. be

...

1. nested;

...

1. configuration

...

1. and

...

1. system

...

1. properties

...

1. will

...

1. be

...

1. used

...

1. for

...

1. substitution

...

1. with

...

1. configuration

...

1. properties

...

1. having

...

1. precedence.

...

2. For

...

1. convenience,

...

1. any

...

1. configuration

...

1. properties

...

1. that

...

1. are

...

1. set

...

1. as

...

1. system

...

1. properties

...

1. are

...

1. copied

...

1. into

...

1. the

...

1. set

...

1. of

...

1. configuration

...

1. properties.

...

1. This

...

1. provide

...

1. an

...

1. easy

...

1. way

...

1. to

...

1. add

...

1. to

...

1. or

...

1. override

...

1. configuration

...

1. properties

...

1. specified

...

1. in

...

1. the

...

1. config.properties

...

1. file,

...

1. since

...

1. the

...

1. Felix

...

1. instance

...

1. will

...

1. never

...

1. look

...

1. at

...

1. system

...

1. properties

...

1. for

...

1. configuration.

...

2. If

...

1. the

...

1. -b

...

1. switch

...

1. was

...

1. used

...

1. to

...

1. specify

...

1. an

...

1. auto-deploy

...

1. directory,

...

1. then

...

1. use

...

1. that

...

1. to

...

1. set

...

1. the

...

1. value

...

1. of

...

1. felix.auto.deploy.dir

...

1. .

...

2. If

...

1. a

...

1. single

...

1. command-line

...

1. argument

...

1. is

...

1. specified,

...

1. then

...

1. use

...

1. that

...

1. to

...

1. set

...

1. the

...

1. value

...

1. of

...

1. org.osgi.framework.storage

...

1. ;

...

1. relative

...

1. paths

...

1. are

...

1. relative

...

1. to

...

1. the

...

1. current

...

1. directory

...

1. unless

...

1. the

...

1. felix.cache.rootdir

...

1. property is set.
2. Add a shutdown hook to cleanly stop the framework, unless the hook is disabled.
3. 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.
4. Use org.apache.felix.main.AutoProcessor

...

1. ,

...

1. which

...

1. will

...

1. automatically

...

1. deploy

...

1. any

...

1. bundles

...

1. in

...

1. the

...

1. auto-deploy

...

1. directory

...

1. as

...

1. well

...

1. as

...

1. bundles

...

1. specified

...

1. in

...

1. the

...

1. felix.auto.install

...

1. and

...

1. felix.auto.start

...

1. configuration

...

1. properties

...

1. during

...

1. framework

...

1. startup

...

1. to

...

1. automatically

...

1. install

...

1. and/or

...

1. start

...

1. bundles;

...

1. see

...

1. the

...

1. usage document for more information configuration properties and bundle auto-deploy.
2. 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()

...

1. and

...

1. some

...

1. libraries

...

1. (e.g.,

...

1. Swing)

...

1. create

...

1. threads

...

1. that

...

1. will

...

1. not

...

1. allow

...

1. the

...

1. VM

...

1. to

...

1. 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:

 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:

{noformat}
launcher/
   lib/
      org.apache.felix.main-23.0.0.jar
   bundle/
      org.apache.felix.shell-1.4gogo.command-0.6.0.jar
      org.apache.felix.gogo.runtime-0.6.0.jar
      org.apache.felix.gogo.shell.tui-10.46.0.jar
   src/
      example/
         Main.java
{noformat}

The {{

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 Felix.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()));
            try
            {
                for (String s = br.readLine(); s != null; s = br.readLine())
                {
                    s = s.trim();
                    // Try to load first non-empty, non-commented line.
                    if ((s.length() > 0) && (s.charAt(0) != '#'))
                    {
                        return (FrameworkFactory) Class.forName(s).newInstance();
                    }
                }
            }
            finally
            {
                if (br != null) br.close();
            }
        }

        throw new Exception("Could not find framework factory.");
    }
}
{code}

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.

}
            m_fwk = getFrameworkFactory().newFramework(null);
            m_fwk.init()
{code}

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()

...

.

}
            AutoProcessor.process(null, m_fwk.getBundleContext());
{code}

The {{AutorProcessor}} will automatically deploy bundles in the 

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

...

installed.

}
            m_fwk.start();
            m_fwk.waitForStop(0);
            System.exit(0);
{code}

These

...

final

...

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
    {
        ...
    }
{code}

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

...

lookup.

...

The

...

following

...

command

...

compiles

...

the

...

launcher

...

when

...

run

...

from

...

the

...

root

...

directory

...

of

...

the

...

launcher

...

project:

}
javac -d . -classpath lib/org.apache.felix.main-23.0.0.jar src/example/Main.java
{noformat}

After

...

executing

...

this

...

command,

...

an

...

example/

...

directory

...

is

...

created

...

in

...

the

...

current

...

directory,

...

which

...

contains

...

the

...

generated

...

class

...

file.

...

The

...

following

...

command

...

executes

...

the

...

simple

...

launcher

...

when

...

run

...

from

...

the

...

root

...

directory

...

of

...

the

...

launcher

...

project:

}
java -cp .:lib/org.apache.felix.main-23.0.0.jar example.Main
{noformat}

After

...

executing

...

this

...

command,

...

a

...

"

...

felix-cache/

...

"

...

directory

...

is

...

created

...

that

...

contains

...

the

...

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

...

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, 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.

Host/Felix Interaction

In the section on launching 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.

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

 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.

{anchor:host-interaction}

h2. Host/Felix Interaction

In the section on [launching|#launching] Felix above, the {{Felix}} 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 {{init()}} on the framework instance and the using {{getBundleContext()}} to get the System Bundle's context, but it can be more convenient to use an activator instance.

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

{code}
public class HostActivator implements BundleActivator
{
    private BundleContext m_context = null;

    public void start(BundleContext context)
    {
        m_context = context;
    }

    public void stop(BundleContext context)
    {
        m_context = null;
    }

    public Bundle[] getBundles()
    {
        if (m_context != null)
        {
            return m_context.getBundles();
        }
        return null;
    }
}
{code}

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);
    }
}
{code}

Notice

...

how

...

the

...

HostApplication.getInstalledBundles()

...

method

...

uses

...

its

...

activator

...

instance

...

to

...

get

...

access

...

to

...

the system 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.

...

...

Providing Host Application Services

Providing services from the host application to bundles inside the embedded Felix framework instance follows the basic approach laid out in above. The main complication for providing a host application service to bundles is the fact that both the host application and the bundles must be using the same class definitions for the service interface classes. Since the host application cannot import classes from a bundle, this means that the service interface classes must be accessible on the class path, typically as part of the host application itself. The host application then must export the service interface package via the system bundle so that bundles installed into the embedded framework instance can import it. This is achieved using the org.osgi.framework.system.packages.extra

...

configuration

...

property

...

previously

...

presented.

...

Consider

...

the

...

follow

...

simple

...

property

...

lookup

...

service:

}
package host.service.lookup;

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

This

...

package

...

is

...

simply

...

part

...

of

...

the

...

host

...

application,

...

which

...

is

...

potentially

...

packaged

...

into

...

a

...

JAR

...

file

...

and

...

started

...

with

...

the

...

"

...

java

...

-jar

...

"

...

command.

...

Now

...

consider

...

the

...

following

...

host

...

application

...

bundle

...

activator,

...

which

...

will

...

be

...

used

...

to

...

register/unregister

...

the

...

property

...

lookup

...

service

...

when

...

the

...

embedded

...

framework

...

instance

...

starts/stops:

}
package host.core;

import java.util.Map;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceRegistration;
import host.service.lookup;

public class HostActivator implements BundleActivator
{
    private Map m_lookupMap = null;
    private BundleContext m_context = null;
    private ServiceRegistration m_registration = null;

    public HostActivator(Map lookupMap)
    {
        // Save a reference to the service's backing store.
        m_lookupMap = lookupMap;
    }

    public void start(BundleContext context)
    {
        // Save a reference to the bundle context.
        m_context = context;
        // Create a property lookup service implementation.
        Lookup lookup = new Lookup() {
            public Object lookup(String name)
            {
                return m_lookupMap.get(name);
            }
        };
        // Register the property lookup service and save
        // the service registration.
        m_registration = m_context.registerService(
            Lookup.class.getName(), lookup, null);
    }

    public void stop(BundleContext context)
    {
        // Unregister the property lookup service.
        m_registration.unregister();
        m_context = null;
    }
}
{code}

Given

...

the

...

above

...

host

...

application

...

bundle

...

activator,

...

the

...

following

...

code

...

snippet

...

shows

...

how

...

the

...

host

...

application

...

could

...

create

...

an

...

embedded

...

version

...

of

...

the

...

Felix

...

framework

...

and

...

provide

...

the

...

property

...

lookup

...

service

...

to

...

installed

...

bundles:

}
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);
    }
}
{code}

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.

...

...

Using Services Provided by Bundles

Using services provided by bundles follows the same general approach of using a host application bundle activator. The main complication for the host application using a service from a bundle is the fact that both the host application and the bundle must be using the same class definitions for the service interface classes. Since the host application cannot import classes from a bundle, this means that the service interface classes must be accessible on the class path, typically as part of the host application itself. The host application then must export the service interface package via the system bundle so that bundles installed into the embedded framework instance can import it. This is achieved using the org.osgi.framework.system.packages.extra

...

configuration

...

property

...

previously

...

presented.

...

Consider

...

the

...

following

...

simple

...

command

...

service

...

interface

...

for

...

which

...

bundles

...

provide

...

implementations,

...

such

...

as

...

might

...

be

...

used

...

to

...

create

...

an

...

extensible

...

interactive

...

shell:

}
package host.service.command;

public class Command
{
    public String getName();
    public String getDescription();
    public boolean execute(String commandline);
}
{code}

This

...

package

...

is

...

simply

...

part

...

of

...

the

...

host

...

application,

...

which

...

is

...

potentially

...

packaged

...

into

...

a

...

JAR

...

file

...

and

...

started

...

with

...

the

...

"

...

java

...

-jar

...

"

...

command.

...

Now

...

consider

...

the

...

previously

...

introduced

...

host

...

application

...

bundle

...

activator

...

below,

...

which

...

simply

...

provides

...

access

...

to

...

the

...

system

...

bundle

...

context:

}
package host.core;

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;

public class HostActivator implements BundleActivator
{
    private BundleContext m_context = null;

    public void start(BundleContext context)
    {
        m_context = context;
    }

    public void stop(BundleContext context)
    {
        m_context = null;
    }

    public BundleContext getContext()
    {
        return m_context;
    }
}
{code}

With

...

this

...

bundle

...

activator,

...

the

...

host

...

application

...

can

...

use

...

command

...

services

...

provided

...

by

...

bundles

...

installed

...

inside

...

its

...

embedded

...

Felix

...

framework

...

instance.

...

The

...

following

...

code

...

snippet

...

illustrates

...

one

...

possible

...

approach:

}
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);
    }
}
{code}

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.

...

...

Using Bundle Services via Reflection

It possible for the host application to use services provided by bundles without having access to the service interface classes and thus not needing to put the service interface classes on the class path. To do this, the host application uses the same general approach to acquire the system bundle context object, which it can use to look up service objects. Using either an LDAP filter or the service interface class name, the host application can retrieve the service object and then use standard Java reflection to invoke methods on the service object.

Other Approaches

The Transloader project is another attempt at dealing with issues of classes loaded from different class loaders and may be of interest.

Caveat

The code in this document has not been thoroughly tested nor even compiled and may be out of date with respect to the current Felix source code. If you find errors please report them so the that they can be corrected.

Feedback

Subscribe to the Felix users mailing list by sending a message to users-subscribe@felix.apache.org; after subscribing, email questions or feedback to users@felix.apache.org.