Moving From Plexus To Guice
- 1. Moving from to
- 2. Why move? ● Plexus is not widely used outside of Maven ● Lack of documentation, not always up-to-date ● Extra steps needed to generate Plexus XML ● Not type-safe, lacks support for generics
- 3. ● Single plexus.xml ● META-INF/plexus/components.xml (Class-Path)
- 4. ● Has annotations, but still need to generate XML
- 5. Why ? ● Standard: reference implementation for JSR 330 ● Flexible: can map all sorts of metadata to bindings ● Type-safe: detailed messages when things go wrong ● Modular: multiple extensions available, OSGi-ready
- 6. JSR 330 ● New standard for Java dependency injection // Constructor injection // Field injection // Setter injection
- 7. ● Fluent Java binding API ● Records generic information lost during erasure ● Can be driven by Java / annotations / XML / ...etc...
- 8. Migration Path ● Preserve investment in legacy Plexus components ● Allow gradual migration to JSR 330 annotations ● Must support mixture of Plexus and JSR 330
- 9. Customizing ● Guice provides an SPI to hook into injections ● TypeListeners called for matching bound types ● Register MembersListeners for custom injection ● Register InjectionListeners for custom lifecycles ● SPI supports binding introspection / rewriting
- 11. -y Beans ● Writing all those listener classes can get tedious ● guice-bean library cuts out most of the work ● You provide a BeanBinder implementation ● that can provide PropertyBinders for each type ● which can supply PropertyBindings for each property ● Bean conventions select field / setter properties
- 13. Metadata ● Canonical form of Plexus bindings ● Captures @Component implementations ● ● Maps @Component bean properties to ● @Requirement settings ● @Configuration settings ● Interns Plexus hint strings to save space
- 14. Scanning for Metadata ● ClassSpace abstraction supplies classes / resources ● Can be backed by Plexus Classworlds or OSGi ● Plexus XML mapped into Plexus annotations ● Plexus annotations are interpolated and stored
- 15. Converting Configuration ● Builds on top of standard Guice TypeConverters ● Supports properties, nested collections, and beans ● Guice SPI lets you add your own TypeConverters
- 16. Locating Components ● Guice bindings map Keys to Providers ● Each Key has a type and optional annotation ● Plexus components have roles and hints Key == Class<Role> + @Named(hint) ● Uses Guice SPI to find component bindings
- 17. Binding Components ● Opposite of locating components ● @Component roles and hints turned into Keys ● Keys used to bind component implementations ● Singleton default, unless strategy is "per-lookup"
- 18. Injecting Requirements ● @Requirement locate Plexus components ● Handles Maps, Lists, instances, and Wildcards ● Loggers automatically configured and injected ● @Configuration convert constant using type
- 19. Managing Lifecycles ● Uses an InjectionListener to listen for bean instances ● Plexus lifecycle "personality" applied after injection ● Reverse lifecycle applied when container disposed ● Need to manage extra metadata (like descriptions)
- 20. Time for a Demonstration!
- 21. Classworlds ● Plexus Container API still depends on Classworlds ● But dependency is much less in guice-plexus-shim ● Just need to write classworlds-shim around OSGi ● ... to get Plexus apps running on OSGi containers
- 22. Extending JSR 330 ● JSR 330 tells us how to mark dependencies ● and qualify them (just like with Plexus hints) ● But it does not say how to mark components
- 23. Identifying JSR 330 components ● Wrap the Class-Path up as a ClassSpace and scan it ● Look for classes with qualifiers such as @Named ● Empty @Named means "use class name" instead ● Binding type found by analysing class hierarchy
- 24. Next Steps ● We can now run Plexus apps on top of Guice ● ... and start separating apps into OSGi bundles ● OSGi lets us dynamically add / remove bundles ● ... but Guice bindings are static
- 25. Next Steps ● How can we resolve this mismatch? ● Find out in "Dynamic Guice Applications" ...
- 26. Links JSR 330 http://code.google.com/p/atinject/ Guice http://code.google.com/p/google-guice/ Spice-Inject http://svn.sonatype.org/spice/trunk/spice-inject OSGi http://www.osgi.org/About/HowOSGi Blog Updates http://www.sonatype.com/people/author/mcculls/
- 27. Questions?
- 28. Transfo rm ing th e w ay so ftw are is m ad e .