Presentation by Peter Kriens at OSGi Users' Forum UK meeting on Nov 16, 2011 in London. Abstract: The OSGi Service Platform is a standard that specifies a comprehensive model of modules that communicate through a powerful, no overhead, Inter Module Communication mechanism: OSGi Services. OSGi enforces module-level isolation that forbids ad hoc cross-module class loading but this conflicts with prevalent Java software patterns that assume application-wide class visibility. OSGi Connect proposes the OSGi programming model without the module-level isolation. This presentation will show you how you can use OSGi Connect to begin to modularize your existing applications with the OSGi programming model with a minimal upfront investment.

1. Services-First
Migration to OSGi
BJ Hargrave (IBM)
Peter Kriens (aQute)
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2. Agenda
• Modularity Maturity Model
• The Brick Wall
• Couplings
• µServices
• What Broker?
• Example
• Conclusion
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3. Modularity Maturity
Model
• 1 Ad Hoc
• 2 Managed
• 3 Contracts
• 4 Fences Page 2 OSGi Alliance Marketing © 2008-2011 . All Rights Reserved,
© IBM Corp. 2011
21.09.2011
•
Inspired by Graham Charters’ excellent OSGi Community Event 2011
5 Optimize presentation @ http://slidesha.re/q8EHFp
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4. Modularity Maturity
Model
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5. 1. Ad Hoc
• Flat, manual class path
• Single name space
• Full visibility and normal
accessibility
• Monolithic
• Highly coupled
• Split Packages
• Add/Shuffle JARs until it works
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6. 1. Ad Hoc
• Flat, manual class path
• Single name space
e l l
H
• Full visibility and normal
accessibility
• Monolithic
AR
•
•
Highly coupled
Split Packages J
• Add/Shuffle JARs until it works
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7. 2. Managed
• Treat JARs as a module
• JAR Identity
• Naming
• Versioning
• Dependencies
• Repositories
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8. 2. Managed
a d
• Treat JARs as a module
n l o
w he t
• JAR Identity
• Naming
D o t
• Versioning
r n e
• Dependencies
n t e
• Repositories
i
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9. 3. Contracts
• Interface based design,
POJOs
• Provide contracts for
each connection
between JARs
• Implementation details
inside the JAR
• Versioning on contracts
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10. 3. Contracts
•
d e r
a
Interface based design,
o
POJOs
• Provide contracts for
l s
s k
s c
a a
each connection
l h
between JARs
• Implementation details
inside the JAR c
• Versioning on contracts
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11. 4. Fences
• Explicitly Import/Export
packages
• Explicitly specify
requirements and capabilities
• Enforce the module
boundaries
• Semantic Versioning
• Side-by-side versioning
supported
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12. 4. Fences
• Explicitly Import/Export
packages
• Explicitly specify
requirements and capabilities
o d!
•
•
Enforce the module
boundaries
Semantic Versioning
Go
• Side-by-side versioning
supported
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13. 5. Optimize
• Exploit concepts for
modules and contracts
• Delegated Control
• Optimize the code base to
leverage new patterns:
• Extender
• Whiteboard
• Repeat
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14. 5. Optimize
• Exploit concepts for
modules and contracts
• Delegated Control
• Optimize the code base to
leverage new patterns:
• Extender
• Whiteboard
• Repeat
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15. Today
1.
Ad Hoc
2. 3.
Managed Contracts
4.
Fences
5.
Optimize
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16. Today
1.
Ad Hoc Enterprise
DI
vn ,C
m ice ing
2. 3.
Ivy Managed Contracts
gu r
saw sp
jig
4.
Fences
5.
Optimize
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17. Today
1.
Ad Hoc Enterprise
DI
vn ,C
m ice ing
2. 3.
Ivy Managed Contracts
gu r OSGi
saw s p
jig
4.
Fences
5.
Optimize
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18. Today
1.
Ad Hoc Enterprise
DI
vn ,C
m ice ing
2. 3.
Ivy Managed Contracts
gu r OSGi
saw s p
jig
4.
Fences
5.
Optimize
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19. woensdag 16 november 11

20. woensdag 16 november 11

21. Class.forName(String)
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22. Class Space
package
class
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23. Class Space
package
class
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24. Class Space
package
class
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25. Class Space
V1 V2
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26. Class Space
V1 V2
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27. Class Space
V1 V2
Class.forName
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28. Class Space
V1 V2
x x
Class.forName
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29. Class Space
V1 V2
x x
Class.forName
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30. Why Class.forName?
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31. Why Class.forName?
! ! !
! ! !
! ! !
! ! !
N G!
P LI
C O U
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32. How to get an Instance?
That is the Question!
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33. Couplings
modular not Example
modular
type FooImpl foo;
Foo foo = (Foo)
instance Class.forName(“FooImpl”)
.newInstance();
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34. Type Coupling
class Client {} class FooImpl{}
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35. Type Coupling
class Client {} class FooImpl{}
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36. Type Coupling
class Client {} class FooImpl{}
interface Foo{}
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37. Type Coupling
class Client {} class FooImpl{}
interface Foo{}
uses implements
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38. Type Coupling
class Client {} class FooImpl{}
interface Foo{}
uses implements
get instance
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39. Type Coupling
class Client {} class FooImpl{}
o
r ?l
o ut s
n einterface Foo{}
C s
uses implements
Is get instance
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40. Instance Coupling
• New
• Factory
• Inversion of Control
• Broker
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41. Instance Coupling
client container impl
• New
• Factory
• Inversion of Control
• Broker
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42. Instance Coupling
client container impl
• New
• Factory
• Inversion of Control
• Broker
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43. Instance Coupling
client container impl
• New
• Factory
• Inversion of Control
• Broker
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44. Instance Coupling
client container impl
• New
• Factory
• Inversion of Control
• Broker
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45. Instance Coupling
client container impl
• New
• Factory
• Inversion of Control
• Broker
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46. µServices Primitive
• Broker Pattern
• Direction
• Contract
• Publish
• Find
• Bind
• Who’s Listening?
• Cardinality
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47. µServices Primitive
• Broker Pattern
• Direction
• Contract
• Publish A S B
• Find
• Bind
• Who’s listening?
• Cardinality
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48. Patterns
• Factory
• Listener
• Discovery
• Distribution
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49. 5. Optimize
E
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50. 5. Optimize
A B C
D E F
G H I
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51. Back to the Brick Wall
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52. Migration
A B C
D E F
G H I
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53. Migration
A B C
D E F
G H I
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54. Migration
A B C
D E F
G H I
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55. Migration
A B C
D E F
G H I
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56. Migration
A B C
D E F
G H I
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57. So we need a broker
that runs without
fences...
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58. So we need a Broker
that runs without
Fences...SR
o j o
P
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59. POJOSR
• Developed by Karl Pauls
• JavaOne presentation 24811
• http://pojosr.googlecode.com
• Based on Apache Felix
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60. Gain
• Existing libraries and many bundles work without
modification
• Bundle (JAR) activation (have their own local main)
• µServices
• Dynamicity (in µServices)
• Extender pattern (react on JAR content)
• Migration path to Fences (OSGi)
• Existing OSGi and non-OSGi tooling can be used
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61. Loss
• No dynamic install/uninstall/update
• No side-by-side versioning
• No module privacy
• No explicit dependencies
• No Lazy activation
• No Bundle classpath
• No Native Code support
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62. Migrating
• Example: extend ant … the tool we all
(sometimes) love and (sometimes) hate
• We make different <helloXXX/> tasks
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63. Ant Your Service
• Base ant
• Activator
• Extender
ant
...
...
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64. Ant Your Service
• Base ant pojosr
ant
• Activator
• Extender
ant
...
...
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65. Ant Your Service
• Base ant pojosr
ant
• Activator
• Extender
ant
...
...
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66. Ant Your Service
Class<Task>
• Base ant pojosr
ant
• Activator
• Extender
ant
...
...
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67. Ant Your Service
Class<Task>
hello
activator
• Base ant pojosr
ant
• Activator
• Extender
ant
...
...
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68. Ant Your Service
Class<Task>
hello
activator
• Base ant pojosr
ant
• Activator
• Extender
ant
...
...
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69. Ant Your Service
<project name="master">
<path id="bundles">
<fileset dir="bundles">
<include name="*.jar" />
</fileset>
</path>
<taskdef name="auto"
classname="aQute.ant.connect.AutoTask" classpathref="bundles" />
<auto />
<helloActivator />
</project>
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70. Ant Your Service
public class Activator implements BundleActivator {
public void start(BundleContext context) throws Exception {
Properties props = new Properties();
props.put("ant", "helloActivator");
context.registerService(Class.class.getName(),
HelloTask.class, props);
}
public void stop(BundleContext context) throws Exception {
}
}
public class HelloTask extends Task {
String message = "Hello Activator";
public void execute() { System.out.println(message); }
public void setMessage(String m) { this.message = m; }
}
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71. Ant Your Service
public class Activator implements BundleActivator {
t
public void start(BundleContext context) throws Exception {
f
Properties props = new Properties();
u
props.put("ant", "helloActivator");
r
context.registerService(Class.class.getName(),
c
HelloTask.class, props);
}
public void stop(BundleContext context) throws Exception {
}
}
public class HelloTask extends Task {
String message = "Hello Activator";
public void execute() { System.out.println(message); }
public void setMessage(String m) { this.message = m; }
}
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72. Ant Your Service
Class<Task>
hello
activator
• Base ant pojosr
pojo
ant
• Activator
• Extender
ant
...
...
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73. Ant Your Service
Class<Task>
hello
activator
• Base ant pojosr
pojo
ant
hello
extendee
• Activator
• Extender
ant
...
...
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74. Ant Your Service
Class<Task>
hello
activator
• Base ant pojosr
pojo
ant
hello
extendee
• Activator
Manifest-Version: 1.0
• ant Ant-Task: helloExtender=HelloTask
Extender
...
...
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75. Ant Your Service
public class HelloTask extends Task {
String message = "Hello Extender";
public void execute() { System.out.println(message); }
public void setMessage(String m) { this.message = m; }
}
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76. Ant Your Service
public class HelloTask extends Task {
String message = "Hello Extender";
public void execute() { System.out.println(message); }
public void setMessage(String m) { this.message = m; }
}
u ft
c r
N O
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77. Conclusion
• Moving to Fences is hard because popular
instance creation patterns are
fundamentally not modular
• Services-First approach works without
Fences
• After completion, moving to Fences is
much easier
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78. Good Fences
Make Good Neighbors
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79. Good Fences
od ul es
Make Good Neighbors
m
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80. Q&A
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