The provisioning of third-party libraries and frameworks within the Apache Felix OSGi implementation has always been a challenge. This occurs due to the case that not every library is available as an OSGi Bundle and not every library is ready to run within an OSGi environment. Especially big frameworks like Hibernate and Apache CXF, with their large number of depending libraries and the way how they work, makes it time consuming to make them OSGi compatible. This presentation addresses the main issues, especially the ones caused by class loading, and shows various approaches on how to resolve these.

1. Third-Party Libraries and OSGi
a complicated relationship

2. Senior Solution Architect
6 years of WCMS experience
Loves working with Java
(script)
Sascha Brinkmann
Hobbies: Biking, Hiking, Travelling
Contact: sb@eggs.de @sasusu
About Me

3. About Us

4. About Us
1984 Foundation year
2004 Adobe Business Partner
2005 Adobe Authorized Training Center
2010 Winner of Siemens top+ Award
2014 100% Adobe focussed for 10 years
Employees: 45
Located: Munich, Germany
Happy Adobe customers: +40

5. ➢ Motivation
➢ Challenge
➢ Analysis Possible Strategies
➢ Tips & Tricks
➢ Conclusion
➢ OSGi Basics
Table of Content

6. Integration of AEM into a heterogeneous IT systems landscape
with interfaces to various subsystems.
AEM
LDAP / Active Directory
Microsoft SharePoint
Microsoft Enterprise Search (FAST)
IBM Lotus Notes Domino
SAP / Hybris
SQL Database
Rest- and Webservices
Amazon S3
Facbook
Twitter
YouTube
Brightcove
Email
FTP
Google Search Appliance
Motivation
InternalExternal

7. Our work is all about solving business problems. Solutions for
almost every technical challenge are provided by third party
libraries from the central maven repository.
Motivation

8. How can I use various types of third party libraries
and frameworks within my projects?
Challenge

9. OSGi Basics
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10. OSGi Basics - Apache Felix
Apache Felix is a fundamental element of the technology stack of
the Adobe Experience Manager (AEM). It provides the
environment for all Java written components.
Java Content Repository (CRX)
Apache Sling
Adobe Experience Manager (WCMS)
OSGi Runtime (Apache Felix)

11. one Classloader for the
whole Java application
one Classloader per OSGi bundle
Bundle B
Bundle A
Bundle C
Bundle D
Library A
Library C
Library B
Library D
OSGi Basics - Classloading
Key difference between traditional Java Applications and
Applications running within OSGi.

12. Bundle
Manifest
Consumes Provides
OSGi Basics - Bundle Structure

13. Bundle Identifier
Packages provided to other bundles
Packages Consumed from other bundles
OSGi Basics - Bundle Manifest
The manifest file is a set of OSGi specific headers. It defines how
to deploy and run the OSGi bundle.

14. Apache Felix
Bundle Plugin
Dependency to
other Bundle
OSGi Basics - Maven POM Config
The Apache Felix Bundle Plugin for Maven enhances artifacts
with the bundle manifest.

15. Strategies to use third party libraries
First Option
Embedding Libraries
Second Option
Libraries as Bundles

16. First Option Embedding Libraries
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17. Bundle
Manifest
First Option - Embedding Libraries
Same classloader for external libraries and bundle classes.

18. Libraries embedded
within the bundle
First Option - Embedding Libraries
Bundle Manifest

19. Dependency to be embedded
with implicit scope ‘compile’
Instruction to embed all
dependencies with scope
compile & runtime
First Option - Embedding Libraries
Maven POM snippet

20. Apache Felix needs to resolve all dependencies prior to
start the bundle.
First Option - Embedding Libraries

21. Transitive dependencies
are not embedded
automatically!
First Option - Embedding Libraries
Maven Artifact Dependency Tree

22. A large number of embedded
libraries within your OSGi bundle ...
… can cause an even larger
number of unresolveable
packages.
First Option - Embedding Libraries

23. Additional dependencies to
resolve the missing packages.
Instruction containing a list of
packages which should be
ignored by Apache Felix.
Instruction to embed
transitive dependencies
First Option - Embedding Libraries
Further configuration parameters to adjust the generated manifest.

24. First Option - Embedding Libraries
The result has to be that the bundle is deployed with no unresolved
packages and activated successfully
Bundle is activated and ready
for operation.

25. Advantages
➢ Easy to archive
➢ Usage is encapsulated
➢ Same classloader between class-files and library
Disadvantages
➢ Usage is limited to bundle
➢ No separation of concerns
➢ Multiple usage in different bundles increase the memory
consumption and the probability of conflicts when sharing
references
First Option - Embedding Libraries

26. Second Option
Libraries as Bundle
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27. Transformation or encapsulation of Java libraries to turn them
into OSGi bundles
Searching for existing OSGi bundles
End of availability after September 2014 Just kicked off
Successor
Commandline Tool Bundle Plugin
Second Option - Libraries as Bundle

28. Second Option - Libraries as Bundle
Advantages
➢ Functionality can be shared across multiple bundles
➢ Separation of concerns
➢ Bundles can be updated independently
➢ Class reference conflicts can be avoided, as there is only one
shared source
Disadvantages
➢ Most libraries are not available as OSGi bundles
➢ Dynamic class resolving via Class.forName() or reflection is
difficult

29. OSGi Basics - Bundles vs. Fragments
the bundle where the fragment is attached to
Bundle
Fragment
Has its own classloader
and lifecycle. Can be
referenced by other
bundles.
Is part of another Bundle
and utilizes its classloader.
Extends the imports and
exports of the host bundle.
Fragment Manifest

30. Hibernate ORM is an object-relational mapping library for the Java
language, providing a framework for mapping an object-oriented domain
model to a traditional relational database.
Entities
and DAO
JDBC
DriverHibernate
Core Bundle
Consumes
Entity
Bridge Consumes
Extends
Extends
OSGi
Fragment
OSGi
Bundle
Second Option - Libraries as Bundle

31. The system bundle is a special bundle that represents the OSGi
framework itself, from within that framework.
Characteristics
➢ Bundle ID 0
➢ It exports packages from the JRE
➢ Only packages which are available in any JVM are provided. All
java* packages for example javax.swing, org.w3c.com etc. are
excluded
➢ Exports the OSGi framework packages such as org.osgi.framework
OSGi Basics - System Bundle

32. Apache Axis2 is a Web Services / SOAP / WSDL engine
and the successor to the widely used Apache Axis SOAP
stack.
System
Bundle
Axis 2
FragmentExtends
Entities
and DAO
Consumes
Second Option - Libraries as Bundle
OSGi
Fragment
OSGi
Bundle

33. Some third party libraries make us of the current thread classloader that definitely runs
within another context than the bundle class loader. To allow the third party library to
access bundle resources, the current thread classloader has to be replaced for this action.
Dealing with Class Loader Issues

34. ➢ There is no best practice. Each framework needs its individual
solution!
➢ Working with third party libraries is like a box of chocolates -
you never know what you're gonna get.
➢ You know it’s working when you see it’s working!
➢ Most frameworks don’t support OSGi or are not properly
tested with Apache Felix.
➢ It needs a community with support from Adobe sharing
experiences and best practices including the use of third party
libraries.
Conclusion

35. Your chance for
remarks and questions!
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36. The End
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37. Presentation
http://www.eggs.de/connectwebex2014
The Author
Sascha Brinkmann - sb@eggs.de
Sales Representative
Martin Brösamle - mb@eggs.de
Get in Touch

38. Terms of Use
This work is licensed under a
Creative Commons Attribution-NoDerivatives
4.0 International License
All photos copyright © Sascha Brinkmann,
all rights reserved.