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Why OSGi matters for Enterprise Java Infrastructures
Santosh Kumar
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Agenda
• Introduction to OSGi
• Why is OSGi technology important
• How OSGi matters for Infrastructure
• OSGi Enterprise spec
• OSGi in Cloud
• Q&A
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Take away from this session• Overall understanding to view OSGi as THE
module system for Java
• Understanding of what this OSGi Enterprise spec is all about
• Should be able to start experimenting with it themselves using one of the available implementations
OSGiKey for Infrastructure
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What is OSGi
OSGi - Open Services Gateway initiative– Technology is the dynamic module system for
Java™.– Provides a service-oriented, component-based
environment for developers– Offers standardized ways to manage the software
lifecycle.– Support for building modular
dynamic and extensible systemsOSGi
Consider as Universal Middleware
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Lets put things in perspective…
The Complexity & Scale of Software requires:
1. Service Oriented
As complexity and size increases Need for higher level of abstract programming
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Why OSGi?2. Modularity
• Java Platform Modularity– Classes encapsulate data– Packages contain classes– Jars contain packages
• Class visibility:private, package private, protected,public
• No “jar scoped” access modifiers.• No means for a jar to declare its dependencies.• No versioning.• Jars have no modularization characteristics
– At runtime, global classpath to search
Jar as unit does not have modularity
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Why OSGi?
3. Versioning– Enterprise Apps have isolated
classpaths but… – Across apps - each archive typically
contains all the libraries required by the application
Common libraries/frameworks get installed with each application
Multiple copies of libraries in memory
– Within apps - 3rd party libraries consume other libraries leading to version conflicts
p lankto n.v1
p lankto n.v2
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Overall Architecture
= serviceHardware
Driver Driver Driver
Operating System
Java
OSGi
Fram
eworkModule (Bundle)
OSGi as module system
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OSGi –The Dynamic Module System for Java
OSGi specifies a modular architecture for dynamic component based systems
• Execution Environment
• Module Layer
• Life Cycle Layer
• Service LayerOSGi introduces
Bundles
as modules
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Module layer
• Bundle - unit of module
• Packaged as JAR - classes + manifest + resources
- Versioning support
- Dependency specification
- JAR with MIME type : application/vnd.osgi.bundle
• OSGi enforces modularity in bundles
Bundle as module represents separation of concerns
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OSGi ClassLoading
• Each bundle has its own classloader / classpath. More efficient for large systems
• Multiple versions of bundles supported concurrently
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Service Layer• Defines a publish/find/bind service model
– Fully dynamic– Intra VM– service registry
• A service is a normal Java object published under one or more Java interfaces with additional metadata with the service registry
• Bundles can register services, search for them, or receive notifications when their registration state changes.
• Service lifecycle is highly dynamic– Service may be published or unpublished at any time
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Service Orientation
Service ProviderService Provider
Service RegistryService Registry
Service ConsumerService Consumer
Service Description
publish find
interact
OSGi intrinsically supports SOA
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Life Cycle
• API to control the security and life cycle operations of bundles
• Install, uninstall, start, stop bundles dynamic without restarting applications
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What does the OSGi Framework provide?
• Horizontal Software Integration Platform
• Component Oriented Architecture– Module (Bundles)
– Package sharing and version management
– Life-cycle management and notification (events)
• Service Oriented Architecture– Publish/find/bind intra-VM service model
– Life-cycle notification (events)
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Framework Features• Runs multiple applications and services
• Single VM instance
• Separate class loader per bundle
– Class loader network
– Independent namespaces
– Class sharing at the Java package level
• Lifecycle management of bundles
• Intra VM publish/find/bind service model
• Java Permissions to secure framework
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Where OSGi is used
• Equinox
– Reference implementation of core framework and various services
– Base runtime for all of Eclipse (rich client, server side and embedded)
• Felix - Ships with GlassFish
• Application servers : Websphere, JBoss etc
• SOA Virtualization Platform : TIBCO Active Matrix
widespread use in desktop and servers
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Does Enterprise Java need OSGi?• Current challenges
– Lots of Libraries To Manage
– Designed for Extensibility
– Dynamic Deployment, Uptime
– Well-defined coherent modules
– Simplify unit of reuse
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OSGI in Enterprise
• Integration of established Java Enterprise Edition technologies into an OSGi Environment
• Multiple, interoperable, dependency injection based component models
• Distributed service model for multiple service platforms and external heterogeneous systems
• Database persistence support
• Enterprise-class life cycle and configuration management
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OSGi Enterprise Spec V4.2• Brings Enterprise technologies and OSGi together - OSGi
Enterprise Expert Group (EEG)
• Using existing Java SE/EE specifications:
– JTA, JPA, JNDI, JMX, WebApps, SCA
– Framework integrates with the Java EE programming model
• Adds Spring-derived component model and dependency injection container – Blueprint Container
Embeded Desktop Enterprise
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What’s happening with OSGi EE
• Apache “Aries” - new Apache incubator project
– deliver set of pluggable Java components enabling an enterprise OSGi application programming model.
• Eclipse Enterprise Modules (“Gemini”)
– collection of subprojects, each of which is an implementation or integration of an enterprise-level technology
• Virgo - Dynamic Enterprise Application Platform
– provide a runtime platform for development of server-side enterprise applications
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Blueprint Components and Service
• Specifies a Dependency Injection container, standardizing established Spring conventions
• Specifies components can be wired together within a bundle
• Components can be published as services to the service registry
• Components configuration and dependencies injected them Blueprint component container ( part of the runtime environment)
• Configuration and dependencies declared in XML “module blueprint”
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Blueprint Components and Service
•Extended for OSGi: publishes and consumes components as OSGi services
• Blueprint standardizes the configuration metadata, and brings governance to the specification of the component model.
• Simplifies unit test outside either Java EE or OSGi r/t.
• The Blueprint DI container is a part of the server runtime (compared to Spring which is part of the application.)
dependencies injected
publishesservice
consumesservice
Blueprint managed bundle Blueprint managed bundle
Blueprint Components （ POJO)
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The Java Persistence API• JPA is a POJO based Object Relational Mapping Framework
– defines an API for persisting
objects into a Relational Database
– API for retrieving Objects
from the database
• JPA - rich API for mapping
arbitrarily complex objects to the underlying database tables
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The JPA Service Specification
An OSGi specification for making JPA work in an OSGi frameworkCore concepts:
> Persistence Bundle : An OSGi bundle containing managed classes a persistence descriptor and a Meta-Persistence manifest header
> Meta-Persistence header : – A header that defines the locations of persistence descriptors in a bundle
> EntityManagerFactory service : An EntityManagerFactory available as an OSGi service
> Persistence Client : A bundle that makes use of an EntityManagerFactory service.
> EntityManagerFactory builder : A factory for incomplete persistence units
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Remote Services
• Extending the OSGi framework to configure existing distributed computing software systems
• Describes how to distribute OSGi services
• Ability for OSGi services to invoke services running in other JVMs
• Support enterprise application topologies for availability, reliability, and scalability
Enables Distributed OSGi
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Web Applications Specification• Defines how to support the Servlet 2.5 and
JavaServer Pages (JSP) 2.1 specifications in OSGi
• Provide deployment of existing and new web applications to Servlet containers operating on the OSGi service platform
• Specification defines the Web Application Bundle, a bundle that performs the same role as the WAR in Java EE
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Web Applications Specification• WAB uses the OSGi life cycle and class/resource loading rules
instead of the standard Java EE environment
• Details web application packaged as a WAR may be installed into an OSGi Service Platform
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SCA Configuration
• Provides an assembly model for distributed applications and systems using a service oriented architecture
• Components that are assembled can be written in different technologies for example Java EE, BPEL, C++, and scripting languages
• Execute on different machines, and can communicate through different protocols and technologies
• Declarative application metadata to enable reflection of an SCA component type definition
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SCA Configuration
• Remote Services specification provides an extendable model for configuration types
• SCA Configuration Type Specification defines such a configuration type
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OSGi on CloudInvestigation underway to find possibility of using OSGi in the
context of cloud computing (RFP 133 Cloud Computing)
IaaSInfrastructure as a
Service
PaaSPlatform as a Service
SaaSSoftware as a Service
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OSGi on Cloud
Value of OSGi : ability to address the following
- Dependency management
- Provisioning/Configuration (Remote services API)
- Extensible, modular system
- Dynamic replacement of components
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Conclusion
Major Java infrastructures support OSGi modular approach
support apps designed & deployed as bundles
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Summary
OSGiKey for Infrastructure OSGi
Consider as Universal Middleware
Bundle as module represents separation of concerns
OSGi increasingly relevant to Enterprise OSGi and Cloud
Synergy having interesting possibilities
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References• http://www.eclipsezone.com/articles/extensions-vs-service
s/
• OSGi Core Spec
• OSGi Enterprise Spec
• http://www.osgi.org
