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Modular Java With Osgi and Karaf


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Modularity is the art of breaking a large system into parts that are easier to understand than the ‘monolithic’ whole.
Failing to achieve the right degree of modularity may lead to development of code that is hard to reuse and to maintain, and when you are working in a team this has a bigger impact on the costs.
The complexity of dealing successfully with modularity is mostly addressed during design, when understanding and planning the dependencies and the behavior of a module, but a good application framework can influence positively toward the right direction by providing a natural environment where to apply good architecture modularity patterns. And OSGi, with its service oriented philosophy and the ecosystem of related tools, where the modules have clear boundaries which coincide with those of ‘Bundles’, it provides such inspiring environment.
During the talk we will illustrate a concrete example of an OSGi project, built with Maven and M2E and running into Apache Karaf. Rather than focusing on the details of technologies, we will put emphasis on the experience of Java modularity so to give a feel of how this platform can help, and allow you to evaluate if this platform can be helpful for your next project and ambitions.

Published in: Technology, Education

Modular Java With Osgi and Karaf

  1. 1. Modular Java with OSGi and Karaf by Cristiano Costantini and Giuseppe Gerla
  2. 2. Modularity
  3. 3. What does “module” means? “A software module is a deployable, manageable, natively reusable, composable, stateless unit of software that provides a concise interface to consumers” Deployable: modules are unit of deployment. Manageable: modules are unit of management. Natively Reusable: modules are a unit of intraprocess reuse. Composable: modules are a unit of composition. Stateless: modules are stateless (*running software from a module has a state). Testability: modules are a unit of testability. uhm… the JAR file! 3
  4. 4. Where to find modularity? 4 There are two facets of Modularity x Development Model x Runtime Model
  5. 5. Why modularity? “Modularity is the best hope to reduce the costs of changes due to architectural decisions” 5 “to tame complexity”
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  8. 8. Modularity in Java 8
  9. 9. Modularity Patterns 9
  10. 10. Modularity Patterns 10 Base Patterns Base patterns advise to design and manage relationships between modules, that you have to emphasize reusability at software module level, and that modules shall be cohesive and have a behavior that serves a singular purpose.
  11. 11. Modularity Patterns 11 Dependency Patterns Dependency patterns teach you that there must be no cycles between modules, that should be organized in levels and in physical layers. And that a module should be independent from the runtime container and deployable independently from other modules.
  12. 12. Modularity Patterns 12 Dependency Patterns: NO CYCLES! NO CYCLES!
  13. 13. Modularity Patterns 13 Usability, Extensibility, Utility Patterns The modules shall have a public interface that is well known. Modules are conﬁgured externally. For improving usability, create a façade serving as a coarse-grained entry point to another ﬁne-grained module. Restricted dependency to theabstract elements of the moduleso to improve extensibility andreduce the number of dependencies. Rely heavily on the use of implementation factories anddependencies injection framework. Separate abstractions from theclasses that implement them inseparate modules, so to helpeliminate module relationships. Perform a levelized build, repeatable build of the modules. This has positive effect on the lifecycle of software development as a levelized build integrate testing that require to integrate early and often, which guarantees a system health always in a good status. Modules should have a test module.
  14. 14. Let’s open pack 1: 14 Development Model x Development Model
  15. 15. Let’s open pack 1: 15 Development Model
  16. 16. Let’s open pack 2: 16 Runtime Model x Runtime Model
  17. 17. Let’s open pack 2: 17 Runtime Model
  18. 18. Karaf
  19. 19. Karaf: an OSGi container Karaf is a small OSGi based runtime which provides a lightweight container onto which various components and applications can be deployed. 19 Apache Karaf can trace it's origins back to the Apache ServiceMix project's Kernel.
  20. 20. Karaf: what is it in detail? Karaf is a platform that allow you to deploy your application. You can install/uninstall/ start/stop your application in several easy way. You can replace/update it and you can change its conﬁguration on the ﬂy. 20
  21. 21. Karaf: what is an application? An application is a composition of modules. Each module can depend from other modules of application or from other module of the container. 21
  22. 22. Karaf: what is a module? A module is a bundle Bundle is a Jar with a Manifest richer than that one We can develop a bundle using Eclipse and Maven 22
  23. 23. Karaf: how a bundle interact? Each bundle can registers one or more service. Each service can be retrieved by other bundle. Each service can obtain the reference of other services. 23
  24. 24. Karaf: What is a service? We can deﬁne a service using the SOA deﬁnition. “A Service is a self-contained unit of functionality” Caution: service in OSGi is NOT a WebService but it is an intra-JVM service. 24
  25. 25. No WebServices? Don’t worry: using Camel you can extend an OSGi service with a WebService and more (as we’ll see later). 25
  26. 26. Karaf & Spring Karaf has its own Dependency Injection API: Blueprint Blueprint is a standard deﬁned in OSGi that allow bean deﬁnition, service deﬁnition and dependency injection Using Spring Dynamic Module we can also use Spring in Karaf. SpringDM explores bundles and load Spring xml ﬁles Spring DM allows you to interact with the world without using OSGi API in our code: in this way the code is cleaner and classes that we write (our modules) can be reused on other platforms. 26
  27. 27. Karaf + Camel = ServiceMix 27 + =
  28. 28. Karaf & Web 28 Pax Web allows Karaf to support web. Using integrated Web Server Jetty, it implements: -HTTP Service API deﬁned in OSGi -Web Application API deﬁned in OSGi Enterprise Like Spring DM, Pax Web explores Bundles installed in Karaf to ﬁnd web.xml ﬁles. When it ﬁnds ithe ﬁlet, Pax Web starts application by creating servlets,ﬁlters and initializing servlet context deﬁned in web deployment descriptor.
  29. 29. SensorMix An example of a Java Modular Application
  30. 30. SensorMix 30 External Architecture
  31. 31. SensorMix 31 Internal Architecture
  32. 32. SensorMix 32 Canonical Data Model Bundle
  33. 33. SensorMix 33 Integration Bundle: Camel routes for sensors’ samples
  34. 34. SensorMix 34 Data Service Bundle: persistence of data
  35. 35. SensorMix Slides: Sensormix: Sensormix Android: Sensormix Arduino:ﬁ/sensormix-arduino/ 35 Links:
  36. 36. Conclusions
  37. 37. Books • “Java Application Architecture: Modularity Patterns with Examples Using OSGi”, Kirk Knoernschild - Prentice Hall • “Spring DM in Action”, A. Cogoluègnes, T. Templier, A. Piper - Manning • “OSGi in Action”, R. S. Hall, K. Pauls, S. McCulloch, D. Savage - Manning • “OSGi In depth”, Alexandre de Castro Alves - Manning • “Enterprise Integration Patterns”, G. Hohpe, B. Woolf - Addison Wesley • “Camel in Action”, C. Ibsen, J. Anstey - Manning 37
  38. 38. Modularity is good Follow Modular Patterns Build modular java software with Maven Run modular java software with Karaf Check SensorMix for an example lesson learnt:
  39. 39. Giuseppe Gerla Cristiano Costantini