Introduction To OSGi

Introduction to OSGiChris Custine

[email protected]

Denver Java User Group - November 12, 2008

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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

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Presentation Agenda

OSGi Overview and History

OSGi Architecture and Layers

Best Practices

Recommended Tools

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What is OSGi?

OSGi - Formerly Open Services Gateway Initiative

Now just OSGi due to generalization of market

OSGi Alliance - Consortium of Vendors

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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

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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

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Where did OSGi come from?

Requirement for standard plugin model for Gateway deviceGUI Model for administration of devicesServices available to devices

Data storage

Conversion

Network

Software management and deploymentSoftware updates

SecurityServices only available to same device/vendorOnly allow updates from properly signed jar

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

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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

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OSGi is...

About building systems from smaller components

Components working together

Managing components

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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()

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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

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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.

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OSGi Architecture and Layers

Execution Environment

Module

Lifecycle

Service

Se

cu

rity

Hardware / OS

Bundles

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Java Execution Environment

Managing the runtime environment

What do I require to run?

JRE Level

GUI Requirements

Matching application requirements with the platform


Module

Lifecycle

Service

Security

Hardware / OS

Bundles

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Module Layer

Packaging and deployment standards

Specify constraints on dependencies and requirements

Visibility between components


Module

Lifecycle

Service

Security

Hardware / OS

Bundles

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Lifecycle Layer

Fine grained events for application and component lifecycle

Installing, starting, stopping

Standard API for registering, listening, and acting on events

No custom API needed for plugins and extensions


Module

Lifecycle

Service

Security

Hardware / OS

Bundles

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Services Layer

Standard methods for registering service instances

Discover and bind to services from other components

Reference tracking


Module

Lifecycle

Service

Security

Hardware / OS

Bundles

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Security Layer

Protect Visibility between components

Example: Vendor A only wants to use the XYZ service provided by Vendor A (could be multiple other implementations of XYZ)

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


Module

Lifecycle

Service

Security

Hardware / OS

Bundles

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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

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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

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Module Layer

Bundles are the primary building block

Package visibility and sharing

Security constraints on packages

Classloader per bundle

Graph of classloaders, resolved at deploy time


Module

Lifecycle

Service

Se

cu

rity

Hardware / OS

Bundles

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Module Layer

Bundle - Just a jar file

META-INF/manifest.mf

Dependencies

Versioning

Consistency


Module

Lifecycle

Service

Security

Hardware / OS

Bundles

� � � � � � � � � � � � � � � � �

� �� 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-ManifestVersion: 2 Bundle-SymbolicName: org.apache.servicemix.kernel.filemonitorBundle-Version: 1.1.0.SNAPSHOTImport-Package: org.apache.commons.logging,org.apache.servicemix.kerne l.filemonitor,org.osgi.framework,org.osgi.service.cm;version="1.2",or g.osgi.service.packageadmin,org.osgi.util.tracker;version="1.3"Export-Package: org.apache.servicemix.kernel.filemonitor;uses:="org.os gi.framework,org.apache.commons.logging,org.osgi.service.cm,org.osgi. service.packageadmin,org.osgi.util.tracker"Bundle-Activator: org.apache.servicemix.kernel.filemonitor.FileMonitorActivatorBundle-Name: Apache ServiceMix Kernel :: File MonitorBundle-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

INSTALLED

UNINSTALLED RESOLVED

STARTING STOPPING

ACTIVE

uninstall resolve

update

uninstall

start

stop

install

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Module Layer - Bundle State

INSTALLED

UNINSTALLED RESOLVED

STARTING STOPPING

ACTIVE

uninstall resolve

update

uninstall

start

stop

install

Resolution of dependencies at deployment

If resolution fails, bundle is not available for use

No runtime CNFE

Services and lifecycle not called until AFTER resolution

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Module Layer - Resolution Goodies

Exporters can name arbitrary attributes for matching

Attributes can be mandatory for matching

org.apache.mypackageb-1.0.0.jar


Export-Package:

org.apache.mypackage;

version=”1.0.0”;flavor=”vanilla”

org.apache.bundlea-1.0.0.jar


Import-Package:


version=”1.0.0”;flavor=”vanilla”

org.apache.mypackagea-1.0.0.jar


Export-Package:


version=”1.0.0”

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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-2.0.0.jar


Export-Package:


version=”2.0.0”

org.apache.bundlea-1.0.0.jar


Import-Package:


version=”[1.0.1,2.0.0)”

org.apache.mypackage-1.0.1.jar


Export-Package:


version=”1.0.1”

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Lifecycle Layer


Module

Lifecycle

Service

Se

cu

rity

Hardware / OS

Bundles

Bundle-Activator: Like main() for your bundle.

Bundles can tap into the lifecycle events of the framework

Extremely powerful when combined with startlevel features

Ability to register listeners for bundle state changes

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Lifecycle Layer


Module

Lifecycle

Service

Security

Hardware / OS

Bundles

Bundle activation provides the bundle context to the bundle

Bundle context provides access 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; }

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Service Layer

Primary means of collaboration between components

Service Registry for discovering and binding to services

Ability to listen for services (Service Tracker)

Service oriented model for in VM interactions

RFC-119 Brings distributed services across instances


Module

Lifecycle

Service

Se

cu

rity

Hardware / OS

Bundles

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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

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OSGi Compendium Services

Log Service

Http Service

Device Access

Configuration Admin

Metatype Service

Preferences Service

User Admin

Wire Admin

IO Connector

Initial Provisioning

UPnP

Declarative Services

Event Admin

Deployment Admin

Auto Configuration

Application Admin

DMT Admin

Monitor Admin

Service Tracker

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Configuration Admin

Configuration provided by framework service

Notification to bundles when configuration changed

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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.)

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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

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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>

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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

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Example: ActiveMQ broker definition using SpringDM and OSGi

broker.xml <bean id="pooledConnectionFactory" class="org.apache.activemq.pool.PooledConnectionFactoryBean"> <property name="maxConnections" value="8" /> <property name="transactionManager" ref="transactionManager" /> <property name="connectionFactory" ref="activemqConnectionFactory" /> <property name="resourceName" value="activemq.${name}" /> </bean> <osgi:reference id="transactionManager" interface="javax.transaction.TransactionManager" cardinality="0..1"/> <osgi:service ref="pooledConnectionFactory"> <osgi:interfaces> <value>javax.jms.ConnectionFactory</value> </osgi:interfaces> <osgi:service-properties> <entry key="name" value="${name}"/> </osgi:service-properties> </osgi:service>

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Example: Using OSGi Configuration Admin for Property Placeholder

beans.xml <bean id="myTransform" class="org.apache.servicemix.examples.camel.MyTransform"> <property name="prefix" value="${prefix}"/> </bean> <osgix:property-placeholder persistent-id="org.apache.servicemix.examples"> <osgix:default-properties> <prop key="prefix">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

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Tour of ServiceMix 4 OSGi Features

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Questions?

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Date post:	10-May-2015
Category:	Technology
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Introduction To OSGi

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