Java EE | Modular EJBs for Enterprise OSGi | Tim Ward

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5. Agenda A Quick EJB refresher

6. How EJBs might fit into OSGi

7. A case study in implementing Modular EJB

8. Proof that it really works

9. Terminology EJB – Enterprise Java Bean

10. EJB JAR – A JAR packaging EJBs

11. Modular EJB – An EJB running in OSGi

12. EJB Bundle – An OSGi bundle packaging Modular EJBs

13. EJBs – the basics EJBs are managed objects, the container injects their dependencies Session EJBs define one or more business “views” These proxy the real EJB object(s)

14. The same view object may delegate to the same, or a different, EJB for successive calls

15. Different EJB types have different delegation styles The EJB runtime adds declarative transactions, security and other services when a business method is called

16. EJB Views and OSGi services EJB View OSGi Service Cardinality May proxy one or many EJB objects One per registration or one per client bundle Location Stored in JNDI Stored in the OSGi service registry Interface One business interface per EJB view One service may expose many interfaces Lifecycle Relatively static once created, no reinjection, no notifications from JNDI Dynamic, may be removed or modified and underlying dependencies may change An EJB view shares a number of concepts with an OSGi service. Page

17. Integrating EJBs with OSGi The service registry is the integration point in OSGi Expose modular EJBs as OSGi services Register one service per EJB view Remote EJB views should be Remoteable Services service.exported.interfaces = * EJB services only work with the right lookup lifecycle Stateless are an interchangable pool

18. Singleton is like a normal service

19. Stateful EJBs are “one per lookup”

20. Identifying EJB Bundles in OSGi Requirement EJB Bundles should be able to be valid EJB JARs

21. Fit with existing OSGi module types (e.g. WABs) Proposal Add a new header “Export-EJB:” Identifies a bundle as an EJB-Bundle

22. Defines which EJBs are exposed as OSGi services

23. Pioneered by Glassfish Application Server Known to work – good basis for a standard?

24. Running Modular EJBs in Aries Apache Aries provides pieces of an OSGi container Integrate with existing projects where possible OpenEJB has been packaged as an OSGi bundle for a couple of releases Some tentative OSGi support, little true integration Mission Statement Integrate OpenEJB with existing OSGi standards and Aries features to provide support for Modular EJBs

25. Issues Running EJBs in OSGi Locating EJBs in OSGi bundles

26. OSGi class loading semantics

27. Building EJB proxy stubs

28. Transaction Manager integration

29. JPA integration

30. Security integration

31. Miscellaneous

32. Working with EJB Bundles – Finding the EJBs EJBs are defined in one of two ways via annotations @Stateless

33. via XML <session>... Requirement 1 says that EJB Bundles should put XML in META-INF/ejb-jar.xml (just like Java EE)

34. Finding the XML is non-trivial for OpenEJB in OSGi Use the extender pattern to help OpenEJB out

35. Recognise bundles using Export-EJB header

36. Working with EJB Bundles – Finding the EJBs (2) Finding Annotated EJBs much harder than for XML Typically a OpenEJB “scans” the classpath by listing files on the file system (using file: or jar: URLs) In OSGi there is no guarantee of the bundle being on the filesystem (or in its original layout) Typical scanning breaks at this point, so either: Try to scan the raw bundle bytes (if they exist!) No fragments, imports or bundle classpath Implement an OSGi aware scanner

37. Apache Aries – Locating META-INF/ejb-jar.xml OpenEJB allows us to build our own EJBModule representing the EJB Bundle

38. An EJBModule allows us to supply a URL to the EJB XML deployment descriptor This is parsed and processed by OpenEJB Aries makes all .xml files in META-INF available Covers other Java EE specs

39. Covers OpenEJB config files

40. Apache Aries – Writing an OSGi aware scanner In OSGi 4.3 a new core API method was added BundleWiring.listResources(String, String, int) We can use this to build an OSGi specific Xbean scanner for our EJBModule for (String resource : bundle.adapt(BundleWiring. class ). listResources( "/" , "*.class" , LISTRESOURCES_RECURSE )) { URL u = bundle.getResource(resource) readClassDef(u.openStream()); }

45. JPA integration

47. Miscellaneous

48. Java EE vs OSGi class loading One of the key differences between OSGi and Java EE is how they load classes

49. Java EE has a hierarchy of ClassLoader instances EJB JAR -> Application -> EJB Container -> Java OSGi has a ClassLoader network...

50. Apache Aries – Classloading for EJB Bundles Clearly the OpenEJB EJBModule ClassLoader should be the EJB Bundle ClassLoader

51. OpenEJB relies on the fact that its internals are visible from the EJB JAR ClassLoader No requirement for EJB Bundles to import OpenEJB

52. Make OpenEJB visible from Application ClassLoader EJB Bundle EJB API Business API

57. JPA integration

59. Miscellaneous Page

60. Implementing EJBs in OSGi EJBs are usually implemented using proxy “stubs” Implement a single business interface

61. May implement other container specific interfaces

62. Often implement javax.naming.Referencable Stubs may be dynamic proxys or generated classes In either case they must be loaded as classes In OSGi each bundle has a different ClassLoader There may not be any one bundle that can see all the interfaces on the proxy!

63. Apache Aries – OSGi safe proxy classes Aries contains an OSGi aware proxy implementation Supports dynamic interface implementation generation for one to N interfaces The proxy allows a parent bundle to be specified The proxy understands that not all interfaces may be visible to the bundle! Aries replaces the default OpenEJB Proxy factory EJB stubs can use any mixture of interfaces

68. JPA integration

70. Miscellaneous Page

71. EJBs and Transactions EJBs have an extremely strong link with transactions All invocations use a global transaction by default More complex interactions can be configured EJBs can control their own transactions too In OSGi we use the JTA Service to get hold of a TransactionManager OpenEJB knows nothing about this... Tx Client

72. Apache Aries – JTA integration Aries contains a JTA Service implementation that uses Geronimo's transaction manager Also provides a TransactionSynchronizationRegistry Aries overrides the OpenEJB transaction manager Use the JTA Service

73. Provide the Tx Manager and Tx Registry This is a clean and well used plug point

78. JPA integration

80. Miscellaneous

81. EJBs and JPA JPA replaced Entity Beans as the persistence strategy for Java EE

82. EJBs have tight integration with JPA Injection via Annotations @PersistenceUnit

83. Injection via XML <persistence-unit-ref> ...

84. JNDI lookup in java:comp/env EJBs may use JPA in two ways Application Managed

85. Container Managed

86. EJBs and JPA – Application Managed In Application managed JPA the EJB manages lifecycle Responsible for creating and closing EntityManagers

87. Responsible for joining any active transactions Adds a dependency on a named persistence unit Injects or looks up an EntityManagerFactory OpenEJB expects to find, create, and manage any persistence units in persistence.xml ClassLoader problems make this impossible in OSGi

88. Apache Aries – Updates to Aries JPA container Aries JPA normally uses the Meta-Persistence header to locate persistence bundles in the framework

89. Java EE also defines rules for finding persistence.xml WARs in WEB-INF/classes, or in WEB-INF/lib

90. EJB JARs in META-INF Aries JPA already checks for Web-ContextPath Add support for the Export-EJB header too

91. Apache Aries – JPA (Application Managed) Hide META-INF/persistence.xml from OpenEJB Don't put the URL in the EJBModule

92. Override the OpenEJB validation failure, Aries JPA will provide the missing EntityManagerFactory! Listen for the registration of OSGi persistence units If the unit is used by an EJB then bind it into the right place in java:comp/env EJB java:comp Extender

93. EJBs and JPA – Container Managed In Container managed JPA the container manages everything! Tx integration

94. Creating and closing EntityManagers More importantly, the container propagates context Different EJBs that use the same persistence unit in a transaction will get the same EntityManager Aries JPA already supports this mode of operation for blueprint beans and OSGi service lookups

95. Apache Aries – JPA (Container Managed) Replace the existing OpenEJB JPA context registry Check for Aries JPA contexts and OpenEJB contexts

96. Cross register any created contexts so both agree! Listen for the registration of OSGi persistence units If the unit is used as a managed context in an EJB then create an OpenEJB managed EntityManager Register this EntityManager in the relevant part of java:comp/env EJB java:comp Extender

101. JPA integration

103. Miscellaneous

104. Java EE Security Java EE supports role-based authorization On Servlet methods

105. On EJB method calls OpenEJB provides a Security Service plugpoint Allows third party authentication/authorization engines to be used Aries has no security component - any volunteers? OpenEJB can cope without a Security Service

106. No integration at this time

111. JPA integration

113. Miscellaneous

114. Issues with OpenEJB in OSGi OpenEJB makes extensive use of XBean internally to build things This has the option of providing a ClassLoader OpenEJB typically provides none OpenEjbVersion throws an ExceptionInInitializerError Attempts to classpath scan for properties To work around these Aries has to extensively set the Thread Context ClassLoader when starting OpenEJB New JAXB code in OpenEJB needs delegating to a 2.1 JAXB implementation every time we build an app

115. Summary There are a few rough edges Some can easily be remedied in OpenEJB internals Some support is clearly missing, but could be added Security, Messaging, EJB lite Broadly speaking, it works And I can prove it! Apache Aries Blog sample with an EJB implemented comment service!

116. References Apache Aries: http://aries.apache.org/ Tim Ward: @TimothyWard [email_address] OSGi and JPA on YouTube: http://www.youtube.com/user/EnterpriseOSGi For more information on Enterprise OSGi take a look at Enterprise OSGi in Action : http://www.manning.com/cummins

Java EE | Modular EJBs for Enterprise OSGi | Tim Ward

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Java EE | Modular EJBs for Enterprise OSGi | Tim Ward