Introduction To OSGi

Introduction to OSGi
Chris Custine
ccustine@apache.org

Denver Java User Group - November 12, 2008

1

Introduction - Chris Custine

Apache ServiceMix - Committer
Open Source ESB
JBI 1.0 Implementation
ServiceMix 4 - OSGi Based (Apache Felix)
Apache Directory Server - Committer and PMC Member
LDAP v3 Certiﬁed
100% Java
Soon to be OSGi, but currently used in some OSGi services
Organic Element - Open Source Consulting and Software
Development

2

Presentation Agenda

OSGi Overview and History

OSGi Architecture and Layers

Best Practices

Recommended Tools

3

What is OSGi?

OSGi - Formerly Open Services Gateway Initiative
Now just OSGi due to generalization of market
OSGi Alliance - Consortium of Vendors

4

What Does the OSGi Alliance Do?

Defines OSGi Service Platform specification
Multiple groups define the specifications
Core Platform Expert Group (CPEG) – Core framework
Mobile Expert Group (MEG) – Mobile
Vehicle Expert Group (VEG) – Automotive
Enterprise Expert Group (EEG) – Enterprise
Residential Expert Group (REG) – Home Automation

5

Where did OSGi come from?

Originally aimed at Home Automation market
Home Gateway device to monitor and interact with devices
Multi vendor devices connected throughout the home

6

Where did OSGi come from?

Requirement for standard plugin model for Gateway device
GUI Model for administration of devices
Services available to devices
Data storage
Conversion
Network
Software management and deployment
Software updates
Security
Services only available to same device/vendor
Only allow updates from properly signed jar

“Hello, this is your refrigerator... you need to buy milk”

7

How we got here

Original use case (Home Automation) faltered around 2000
OSGi used in niche areas (automotive, mobile) for several
years
Eclipse 3.0 released June 2004 - First Eclipse with OSGi
Gradual adoption and recognition for OSGi after Eclipse
Currently undergoing widespread adoption

8

OSGi is...

About building systems from smaller components
Components working together
Managing components

9

Why OSGi?

Convergence of mobile and embedded devices creates
huge manageability problems
Portability - Hardware, OS
Management - Massive pushes for updates and ﬁxes
Maintenance - Dynamic library management and
dependencies causing unmanageable hacks like
Class.forName()

10

OSGi Relationship with Java

Always focused on Java
Bundles may contain native libraries used via JNI
Example: Eclipse uses native libraries for SWT GUI calls
RFC-119 for distributed OSGi allows communication with
external systems (possibly not Java)
Script language support from bundle providers

11

OSGi Service Platform

Two distinct specifications
Core Specification - Core framework, packaging,
modularity, security, API (interfaces), etc.
Service Compendium - Additional services (some optional),
utilities, logging, event system, configuration admin, etc.

12

OSGi Architecture and Layers

Service

Lifecycle

Security
Bundles
Module

Execution Environment

Hardware / OS

13

Java Execution Environment

Managing the runtime environment
Service

What do I require to run? Lifecycle

Security
Bundles

JRE Level Module


GUI Requirements Hardware / OS

Matching application requirements with the platform

14

Module Layer

Packaging and deployment
standards Service

Lifecycle

Security
Specify constraints on
Bundles
Module

dependencies and requirements Execution Environment

Hardware / OS

Visibility between components

15

Lifecycle Layer

Fine grained events for
application and component Service

lifecycle
Lifecycle

Security
Bundles
Module

Installing, starting, stopping Execution Environment

Standard API for registering,
Hardware / OS

listening, and acting on events
No custom API needed for
plugins and extensions

16

Services Layer

Standard methods for registering
service instances Service

Lifecycle

Security
Discover and bind to services
Bundles
Module

from other components Execution Environment

Hardware / OS

Reference tracking

17

Security Layer

Protect Visibility between
components Service

Lifecycle

Security
Example: Vendor A only wants to Bundles
Module

use the XYZ service provided by Execution Environment

Vendor A (could be multiple other Hardware / OS

implementations of XYZ)
Constraints can be expressed
using certiﬁcates from signed jars
or attributes for bundle, service,
etc.

18

Layer Details

Module, Lifecycle, and Service layers are where most work
is done for enterprise Java development
Security is important but not as widely utilized

19

Java Modularity Limitations

Scoping and visibility is limited to packages (no module
scoping)
Dependency management? Managed through classpath
Version handling? First package match on classpath
Modularity is not supported as a ﬁrst class citizen

20

Module Layer

Bundles are the primary building
block
Service

Lifecycle

Security
Package visibility and sharing
Bundles
Module

Security constraints on packages

Hardware / OS

Classloader per bundle
Graph of classloaders, resolved at
deploy time

21

Module Layer

Bundle - Just a jar ﬁle Service

Lifecycle

Security
Bundles

META-INF/manifest.mf
Module


Hardware / OS

Dependencies
Versioning
Consistency

Manifest-Version: 1.0
Import-Package: ...
Export-Package: ...
Bundle-Activator: ...
Bundle-Version: 1.1.0.SNAPSHOT
Bundle-Name: ...
Bundle-ManifestVersion: 2
Bundle-SymbolicName: ...

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Module Layer - Example Manifest


Bundle-SymbolicName: org.apache.servicemix.kernel.filemonitor
Import-Package: org.apache.commons.logging,org.apache.servicemix.kerne
l.filemonitor,org.osgi.framework,org.osgi.service.cm;version=quot;1.2quot;,or
g.osgi.service.packageadmin,org.osgi.util.tracker;version=quot;1.3quot;
Export-Package: org.apache.servicemix.kernel.filemonitor;uses:=quot;org.os
gi.framework,org.apache.commons.logging,org.osgi.service.cm,org.osgi.
Text
service.packageadmin,org.osgi.util.trackerquot;
Bundle-Activator: org.apache.servicemix.kernel.filemonitor.FileMonitorActivator
Bundle-Name: Apache ServiceMix Kernel :: File Monitor
Bundle-Description: This bundle monitors the deploy directory for new
OSGi bundles in jar form, expanded form or for configuration f
ile changes and undeploys/redeploys them

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Module Layer - Bundle Contents

Bundles may contain additional contents not
usually included in jars.
Native code - Multiple platforms, OS, etc.
loading rules specified in manifest
Embedded jar files - Bundle-Classpath allows
embedded jars to be referenced from
manifest.mf (not recommended)
Resource files - images, configuration, html

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Module Layer - Bundle State

install

update
INSTALLED

uninstall resolve

uninstall
UNINSTALLED RESOLVED

start

STARTING STOPPING

stop

ACTIVE

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Module Layer - Bundle State

Resolution of dependencies at
deployment install

INSTALLED
update

If resolution fails, bundle is not
uninstall resolve

uninstall
UNINSTALLED RESOLVED

available for use
start

STARTING STOPPING

stop

No runtime CNFE ACTIVE

Services and lifecycle not
called until AFTER resolution

31

Module Layer - Resolution Goodies

Exporters can name arbitrary attributes for matching
Attributes can be mandatory for matching

org.apache.mypackagea-1.0.0.jar org.apache.mypackageb-1.0.0.jar

META-INF/manifest.mf META-INF/manifest.mf
Export-Package: Export-Package:
org.apache.mypackage; org.apache.mypackage;
version=”1.0.0” version=”1.0.0”;ﬂavor=”vanilla”

org.apache.bundlea-1.0.0.jar

Import-Package:
org.apache.mypackage;
version=”1.0.0”;ﬂavor=”vanilla”

32

Module Layer - Resolution Goodies

Same package can be installed with different versions
Importers can specify version ranges for compatibility
Allows staged migration of multiple components
org.apache.mypackage-1.0.1.jar org.apache.mypackage-2.0.0.jar

META-INF/manifest.mf META-INF/manifest.mf
Export-Package: Export-Package:
org.apache.mypackage; org.apache.mypackage;
version=”1.0.1” version=”2.0.0”

org.apache.bundlea-1.0.0.jar

Import-Package:
org.apache.mypackage;
version=”[1.0.1,2.0.0)”

33

Lifecycle Layer

Bundle-Activator: Like main() for Service

your bundle. Lifecycle

Security
Bundles

Bundles can tap into the lifecycle
Module


events of the framework Hardware / OS

Extremely powerful when
combined with startlevel features
Ability to register listeners for
bundle state changes

34

Lifecycle Layer

Bundle activation provides the Service

bundle context to the bundle Lifecycle

Security
Bundles
Module

Bundle context provides access

Hardware / OS

to the framework and all services
Creates and registers service
instances
Get reference to required services
Register listeners for bundle
lifecycle BundleActivator.java
package org.osgi.framework;

public interface BundleActivator {
public void start(BundleContext context) throws Exception;
public void stop(BundleContext context) throws Exception;
}

35

Service Layer

Primary means of collaboration
between components
Service

Lifecycle

Security
Service Registry for discovering
Bundles
Module

and binding to services Execution Environment

Hardware / OS

Ability to listen for services
(Service Tracker)
Service oriented model for in VM
interactions
RFC-119 Brings distributed
services across instances

36

Start Level Service

Setting bundle start order
Similar to Unix init scripts
Start level can be changed up and down at runtime
Persistent start level on restarts

37

OSGi Compendium Services

Log Service UPnP
Http Service Declarative Services
Device Access Event Admin
Conﬁguration Admin Deployment Admin
Metatype Service Auto Conﬁguration
Preferences Service Application Admin
User Admin DMT Admin
Wire Admin Monitor Admin
IO Connector Service Tracker
Initial Provisioning

38

Configuration Admin

Configuration provided by framework service
Notification to bundles when configuration changed

39

Best Practices

Use package names consistently - We use package name
for artifact name (Eclipse plugins do too), with one package
heirarchy per bundle. Quick recognition of artifact and
package purpose.
Keep public and private classes in separate packages
Use explicit Import-Package. Don’t use Require-Bundle.
Easy to use initially, but causes problems down the road.
Avoid Dynamic-Import - Defers classloading to runtime
Allows arbitrary Class.forName() use case but causes trouble
Use tools to compose manifest ﬁles and package bundles
(Maven plugins, Eclipse PDE, etc.)

40

Tools for OSGi - BND

Peter Kriens - BND
Tool for analyzing dependencies and validating manifest.mf
Uses reﬂection to analyze imports and lists dependencies
Great tool for analyzing non-OSGi jar ﬁles and converting

41

Tools for OSGi - Maven Felix Plugin

Uses BND to automate creation of manifest.mf
Use packaging=bundle to invoke plugin in package lifecycle
pom.xml

<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<configuration>
<instructions>
<Bundle-SymbolicName>${pom.artifactId}</Bundle-SymbolicName>
<Export-Package>org.apache.servicemix.kernel.gshell.activemq;version=${project.version};-
split-package:=merge-first</Export-Package>
<Import-Package>
org.apache.geronimo.gshell.wisdom.command,
org.apache.servicemix.kernel.gshell.core,
org.apache.geronimo.gshell.wisdom.registry,
*
</Import-Package>
<Private-Package>!*</Private-Package>
<Spring-Context>*;publish-context:=false;create-asynchronously:=false</Spring-Context>
</instructions>
</configuration>
</plugin>

42

Tools for OSGi - Spring DM

SpringDM bridges the Spring world with OSGi Service
Platform
Reuse existing knowledge of Spring
Limited knowledge of OSGi required
Expose spring beans in the OSGi Service Registry
Can be bound to by pure OSGi service consumers
Lookup and bind bean refs to OSGi services

43


Example: ActiveMQ broker deﬁnition using SpringDM and
OSGi
broker.xml

<bean id=quot;pooledConnectionFactoryquot; class=quot;org.apache.activemq.pool.PooledConnectionFactoryBeanquot;>
<property name=quot;maxConnectionsquot; value=quot;8quot; />
<property name=quot;transactionManagerquot; ref=quot;transactionManagerquot; />
<property name=quot;connectionFactoryquot; ref=quot;activemqConnectionFactoryquot; />
<property name=quot;resourceNamequot; value=quot;activemq.${name}quot; />
</bean>

<osgi:reference id=quot;transactionManagerquot; interface=quot;javax.transaction.TransactionManagerquot;
cardinality=quot;0..1quot;/>

<osgi:service ref=quot;pooledConnectionFactoryquot;>
<osgi:interfaces>
<value>javax.jms.ConnectionFactory</value>
</osgi:interfaces>
<osgi:service-properties>
<entry key=quot;namequot; value=quot;${name}quot;/>
</osgi:service-properties>
</osgi:service>

44


Example: Using OSGi Conﬁguration Admin for Property
Placeholder

beans.xml

<bean id=quot;myTransformquot; class=quot;org.apache.servicemix.examples.camel.MyTransformquot;>
<property name=quot;prefixquot; value=quot;${prefix}quot;/>
</bean>

<osgix:property-placeholder persistent-id=quot;org.apache.servicemix.examplesquot;>
<osgix:default-properties>
<prop key=quot;prefixquot;>MyTransform</prop>
</osgix:default-properties>
</osgix:property-placeholder>

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Conclusion

OSGi forces planning and engineering of bundle
interactions
More work up front, but rewards come later
No silver bullet, bad code and bad ideas are still bad
Many built in features and services provided for applications
Modularization is rewarded when creating new systems and
modifying existing ones

46

Tour of ServiceMix 4 OSGi Features

47

Introduction To OSGi

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