The session details are accessible over here: http://www.eventreg.com/cc250/sessionDetail.jsp?SID=314613 Session abstract Nowadays, every platform considers having the "OSGi supported" checkbox ticked and offers "easy" and "smooth" migration from the classical Java EE world to the new "modular" future. In spite of the multiple guidelines and best practices, migrating from a monolithic Java EE application to OSGi remains a pain and reveals a number of hidden and time-consuming pitfalls and hurdles. The session will guide you through the usual problems that every project faces on its way to holy modularity, providing helpful tips and tricks on how to quickly find your way through the maze of NoClassDeffFound, ClassCast, and other OSGi-specific errors.

1. S314613:
OSGI Migration
headaches
Krasimir Semerdzhiev
SAP Labs Bulgaria
Development Architect
Peter Peshev
SAP Labs Bulgaria
Development Architect

2. Agenda
OSGI intro
Headaches
Painkiller options
Q&A

3. Modularity

4. Alternative implementations
VW Golf
91-97

5. Good architecture and interchangeable
minilang party pos. product workeffort workflow …
accounting assetmaint content bi ebay ecommerce googlebase
guiapp hhfacility manufact. marketing minerva oagis order
Application layer
common catalina base datafile entity widget …
resolver rome serializer servlets tomcat xalan bsf
mail mx4j naming jetty poi wsdl4j bsh
jenks jpos18 jython looks lucene xerces velocity
jakarta jcl json jdbm jdom xmlapis ws-commons
log4j barcode4j axis batik commons xmlrpc geronimo
httpunit freemarker ezmorph fop derby xmlgraphics Libs..
Java VM
rt jce jsse plugin sunjce_prov. dnsns ..

6. Problem: CLASSPATH
Java VM party common resolver axis xerces
Begin rt
jce
assetmaint
hhfacility
catalina
base
mail
jenks
ezmorph
servlets
xmlapis
xmlrpc
Here jsse pos. datafile jakarta jetty xmlgraphics
plugin content entity log4j looks
sunjce_prov manufact. widget httpunit jdbm
.
dnsns product … mx4j bsf
.. bi rome batik bsh Class
marketing workflow jpos18 fop velocity
workeffort ecommerce jcl tomcat ws-commons
Not
ebay oagis barcode4j poi geronimo Found
minerva … freemarker lucene ..
Exception
minilang googlebase serializer jdom json
accounting order naming commons xalan
guiapp ofbiz jython derby wsdl4j

7. The OSGi Alliance
 Started March 1999 as an initiative from ERICSSON, SUN and IBM
 Today: A stable Alliance with almost 100 members
 Now practically all of the Java Server vendors are represented there
 A standardization body…

8. OSGi Framework Layers
Staircase
 Applications can make use
of different layers directly
 Module Layer defines
packaging , deployment
dependancies among
modules
 Lifecycle Layer controls
lifecycyle operations of a
bundle

9. Module Layer: Bundles
Bundles
 Are JAR files
 Contain classes, other resources like HTML, images, specific metadata
 Contain
manifest file (META-INF/MANIFEST.MF) with OSGI specific
headers used to manage the bundle
 Describes the content of the JAR file
 Export Import package
 Require-Bundle

10. Module Layer: Runtime class loading
load class com.foo.classA

11. Class Loading Architecture: Class Space

12. Class Loading Architecture: Delegation
Basic properties
 Parent delegation
 Wire importers and exporters
 There can be fragment bundles
 Class loading traversal based on importers and their wires

13. Lifecycle Layer
Runtime representation of bundles
 Forevery bundle, the framework creates a Bundle java object
 Bundles are identified by Bundle ID, Bundle Symbolic Name and
Bundle Location
 Bundle has a runtime state:

14. What is the story?
Web Web Module bundle
Web Module
Web Modules Modules (war)
(war) bundle
Web Modules bundle
Web Modules
State 2
bundle
Lib Lib Lib Lib EAR file
EAR file OSGi framework
Java EE compliant runtime
bundle bundle bundle
bundle bundle bundle
bundle bundle bundle
bundle bundle bundle
bundle bundle bundle
OSGi framework

15. What do we aim to get from OSGi?
■ Standardized execution environment
■ Java-based modularization
■ Well defined module contract
■ Strict dependency management at build and run time
■ Manifest as a single point of truth
■ Deterministic declarative runtime resolution
or in other words…
■ Evolve from JARs/modules to “interchangeable/reusable parts”

16. Agenda
OSGI intro
Headaches
Painkiller options
Q&A

17. Step 1: Choose an OSGi runtime

18. Step 2: How to create bundles?
Manifest-Version: 1.0
Bundle-Name: My First Bundle
Bundle-SymbolicName: com.acme.myfirstbundle
Bundle-Version: 1.0.0
Bundle-Description: Small Bundle
Bundle-Vendor: ACME
Bundle-Activator: com.acme.myfirstbundle.impl.Activator
Bundle-Category: example
Import-Package: org.osgi.framework
Export-Package: com.acme.myfirstbundle.api
Export-Package ::= export(‘,’ export)*
export ::= package-names(‘;’ parameter)*
package-names ::= package-name(‘;’ package-name)*
Import-Package ::= import(‘,’ import)*
import ::= package-names(‘;’ parameter)*
package-names ::= package-name(‘;’ package-name)*
Require-Bundle ::= bundle-description ( ',' bundle-description )*
bundle-description ::= symbolic-name (';' parameter )*

19. Step 2: How to create bundles?
Let‘s take one example – Apache Derby
org.apache.derby.*
authentication iapi.services.timer impl.jdbc.authentication impl.store.access.sort
catalog iapi.services.uuid impl.load impl.store.raw
catalog.types iapi.sql impl.services impl.store.raw.data
database iapi.sql.compile impl.services.bytecode impl.store.raw.log
diag iapi.sql.conn impl.services.cache impl.store.raw.xact
iapi iapi.sql.depend impl.services.daemon impl.store.replication
iapi.db iapi.sql.dictionary impl.services.jce impl.store.replication.buffer
iapi.error iapi.sql.execute impl.services.jmx impl.store.replication.master
iapi.jdbc iapi.store impl.services.jmxnone impl.store.replication.net
iapi.security iapi.store.access impl.services.locks impl.store.replication.slave
iapi.services iapi.store.access.conglomerate impl.services.monitor impl.tools
iapi.services.cache iapi.store.access.xa impl.services.reflect impl.tools.sysinfo
iapi.services.classfile iapi.store.raw impl.services.stream info
iapi.services.compiler iapi.store.raw.data impl.services.timer io
iapi.services.context iapi.store.raw.log impl.services.uuid jdbc
iapi.services.crypto iapi.store.raw.xact impl.sql loc
iapi.services.daemon iapi.store.replication impl.sql.catalog mbeans
iapi.services.diag iapi.store.replication.master impl.sql.compile osgi
iapi.services.i18n iapi.store.replication.slave impl.sql.conn security
iapi.services.info iapi.tools impl.sql.depend shared
iapi.services.io iapi.tools.i18n impl.sql.execute shared.common
iapi.services.jmx iapi.types impl.sql.execute.rts shared.common.error
iapi.services.loader iapi.util impl.store shared.common.sanity
iapi.services.locks impl impl.store.access tools
iapi.services.memory impl.db impl.store.access.btree vti
iapi.services.monitor impl.io impl.store.access.btree.index
iapi.services.property impl.io.vfmem impl.store.access.conglomerate
iapi.services.stream impl.jdbc impl.store.access.heap

20. Step 2: How to create bundles?
Apache Derby – impl.* gone
org.apache.derby.*
authentication iapi.services.timer osgi
catalog iapi.services.uuid security
catalog.types iapi.sql shared
database iapi.sql.compile shared.common
diag iapi.sql.conn shared.common.error
iapi iapi.sql.depend shared.common.sanity
iapi.db iapi.sql.dictionary tools
iapi.error iapi.sql.execute vti
iapi.jdbc iapi.store
iapi.security iapi.store.access
iapi.services iapi.store.access.conglomerate
iapi.services.cache iapi.store.access.xa
iapi.services.classfile iapi.store.raw
iapi.services.compiler iapi.store.raw.data
iapi.services.context iapi.store.raw.log
iapi.services.crypto iapi.store.raw.xact
iapi.services.daemon iapi.store.replication
iapi.services.diag iapi.store.replication.master
iapi.services.i18n iapi.store.replication.slave
iapi.services.info iapi.tools
iapi.services.io iapi.tools.i18n
iapi.services.jmx iapi.types
iapi.services.loader iapi.util
iapi.services.locks info
iapi.services.memory io
iapi.services.monitor jdbc
iapi.services.property loc
iapi.services.stream mbeans

21. Step 2: How to create bundles?
Apache Derby – what Eclipse uses out of it :-)
org.apache.derby.*
authentication
database
io
jdbc
vti How to create manifests?
 By hand
 BND tool
 Apache Felix Maven plugin
 Eclipse PDE
 Bundlor
or in other words…
■ Don’t rush to define manifests, for modules you know nothing of!

22. Step 3: Let‘s try to activate the bundle.
java.lang.NoClassDefFoundException Class definition is
missing!
The forName() method in class Class.
Possible causes? The findSystemClass method() in class ClassLoader.
The loadClass() method in class ClassLoader
 Missing import-package
 Missing export-package
 Import version mismatch [1.2.3, 2.0); “1.2.3”
 Forgotten/missing component (really missing!)
 Wrong boot class delegation property
 Missing file system permissions (can’t read the JARs)

23. Step 3: Separate a the first library as a bundle
java.lang.NoClassDefFoundError Class definition is
found, but
instantiation failed!
Possible causes?
 Exception in static block
 Missing imported class (NoClassDefFoundException for it)
 Class version mismatch
 Hotspot reflection JIT optimizations (BugID 6265952 )
(injection of sun.misc.Unsafe.defineClass)
or in other words…
■Don’t rush blaming the framework! Classloading there is quite solid!

24. Step 4: Iterative refactoring
My bundle is not updated?!
Possible causes?
 Didyou update the version?
 You’re replacing your bundle directly in the equinox plugins folder
 Package-imports do not fit to the new bundle version?
or in other words…
■Don’t rush blaming the framework! ;)

25. Step 4: Iterative refactoring
java.lang.ClassCastError
Possible causes?
 Additionalcopies (besides the system bundle) of the
OSGi framework classes
 Undesired additional JARs in classpath
■ Clash between RT.jar and application libs
(previously used embedded jars)
■ Java SE 5 vs. Java SE 6 does make a difference…
(a bunch of new packages added (StAX, JDBC 4.0, JAXB 2.0, etc.)
or in other words…
■Make sure you understand the root cause. (try using Eclipse Memory Analyzer)

26. Step 4: Iterative refactoring
Works in Eclipse, but doesn‘t work in Equinox
Possible issues
■ Different setting of org.osgi.parentClassloader
■ app (default for Eclipse)
■ boot
■ ext
■ fwk
 Certain expectations of org.osgi.framework.system.packages
 Different values of org.osgi.framework.bootdelegation
■ property osgi.compatibility.bootdelegation (default for Eclipse is false)
or in other words…
■Don’t be fooled by configuration differences

27. Step 4: Design flaws
Dependencies on startup order
Possible causes?
■ Avoid lookup-error-fail patterns
■ As a last resort – you can use start levels
■ Keep Activators really lean.
■ Typically seen when extracting code from a web module with fixed
Servlet.init() order.
or in other words…
■Don’t do anything needless in your activator. That’s not init()/start()!

28. Step 4: Design flaws
Classloader resource assumptions
Possible issues
■ JAR files
■ Folder containing class files/packages
■ URLs (to any of the above)
■ new File(<resource>), after loader resources iteration
“bundle:xxx” as a resource
or in other words…
■Don’t make assumptions on the classloader resources!

29. Step 4: Design flaws
Boot delegation specifics
■ org.osgi.framework.bootdelegation – shortcut the OSGi resolution
■ Adding com.foo.* includes all sub-packages, but not the com.foo
package itself.
■ osgi.compatibility.bootdelegation - true/false
or in other words…
■Make sure that you understand the setup of your OSGi environment

30. Step 5: Design flaws
SPI pattern limitations
Possible issues
■ Load a class, described in some meta-data file, used via interface
■ META-INF/services/javax.xml.ws.spi.Provider
■ Explicit import of the impl packages is required!

31. Step 5: Design flaws
My process exits unexpectedly?!
Possible issues
■ Lots of code is written with the assumption that it owns the world and not
that it lives in a small corner of it.
■ Enabling a Security Manager which traces System.exit() and Runtime.halt()
calls might help

32. Step 5: Design flaws
Registering objects in the VM has direct impact on the
ability to stop a bundle
Some of those
have no
Possible issues unregister methods!
■ System in and out streams
■ Shutdown hooks
■ MBean server factory
■ Log4J formatters
■ JNDI provider/factory
or in other words…
■Don’t try to do the job of the underlying middleware.

33. Step 5: Design flaws
ContextClassLoader usage
Possible issues
■ Some code written to run in a web app might make some assumptions on
the Context classloader.
■ One example here is JNDI.
or in other words…
■Consider environment dependencies when extracting code into bundles

34. Agenda
OSGI intro
Headaches
Painkiller options
Q&A

35. Eclipse Virgo shell improvements
Supportability commands
■ Nested OSGi frameworks
■ Classloading

36. SpringSource Tool Suite

37. Other relevant sessions
Tue 12:00 PM Developing OSGi-Enabled Java EE Applications
Tue 6:00 PM Patterns for modularity
Tue 6:00 PM OSGI BOF
Tue 9:00 PM OSGi at a Large-Scale Enterprise: Lessons from eBay
Wed 10:00 AM Java EE OSGi applications : Design and Deployment for On-Premises and Cloud
Wed 1:00 PM OSGi and JSR 294: Module Keyword
Wed 4:45 PM Visualizing the Science of Conversation with JavaFX and OSGi to Save Lives
Thu 3:30 PM Creating Modular Applications with Apache Aries and OSGi
Thu 3:30 PM Developing Rich Modular Clients with Java, JavaFX and OSGi Technology

38. Q&A?

39. Thank you!
Krasimir Semerdzhiev
krasimir.semerdzhiev@sap.com
Peter Peshev
peter.peshev@sap.com