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These capabilities may be added in the future, possibly with the help of OSGi.
Framework Choice
After analyzing the available options, we have selected the Spring framework, version 3.
Popular frameworks that support the dependency injection pattern include Spring, PicoContainer, and Guice.
How do they compare? Several articles have been written comparing Spring and Guice, as well as all three. As many have pointed out, Spring and Guice are more than DI frameworks. For our purposes, we should consider considered the attributes of each that are most relevant to the problem at hand:
| Spring | PicoContainer | Guice |
|---|---|---|---|
Supports start/stop lifecycle hooks for components | Yes (interface, JSR-250 @PostConstruct/@PreDestroy annotations, spring-specific annotation, or xml-configured) | Yes (interface or JSR-250 @PostConstruct/@PreDestroy annotations) | |
Supports autowiring | Yes | Yes | Yes |
Supports in-code wiring and configuration | Yes (JavaConfig) | Yes | Yes |
Supports external wiring (outside of code) | Yes (xml) | No | Not directly (but it's possible) |
Supports external config (outside of code) | Yes (xml and/or properties) | No | Yes (Names.bindProperties) |
OSGi-Friendly | Yes (Spring-DM) | Unknown | Yes (Guice-Peaberry) |
JSR-330 Support | |||
Jar Footprint (non-OSGi) | 750kb | 300kb | 650kb |
Spring was selected because:
- It provides an out-of-box and commonly-used way to wire and configure modules ("beans"), outside of code.
- It supports JSR-250 annotations for module lifecycle hooks
- Its OSGi-friendliness is well-documented
Implementation Strategy/Principles
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Implementation Plan
Overview + Discussion
View presentation from March 16th, 2010 Special Topic Meeting
Phase I - Prepare
- List all dependents of existing module interfaces
Identify and remove unused modules and classes with module dependencies. - Remove ReportServlet - FCREPO-646
- Remove ThreadMonitor - FCREPO-647
- Identify circular module dependencies (noted with
on above page).
...
- Decouple module interface impl from Module abstract class where needed
- Push param validation responsibility down to each impl (not in Module)
- Use constructor injection if possible. For those with circular dependencies that can't be refactored easily, provide setters.
- Where existing modules look at configuration of other modules, get the configuration value from a getter in the interface, not the configuration.
- Where existing modules look at global fcfg values, make those available via bean-style class, GlobalConfig.
- Where existing modules look at datastore fcfg values, inject the connectionpool or config values directly.
- Constructors for impls should do as much arg validation/setup as they can. If they can't do it all, it should be done in a @PostConstruct void init() method. In either case, if validation or setup fails, an unchecked exception should be thrown, as per JSR-250.
- Where de-initialization is needed, a @PreDestroy void destroy() method should be used. Errors encountered during de-initialization should be logged by this method, and an unchecked exception should be thrown, as per JSR-250.
Tasklist Modifications Needed Modifications Needed || Completed || Priority || Locked || CreatedDate || CompletedDate || Assignee || Name || |F|M|F|1268080202735| F | M | F | 1268080202735 | | cwilper | Add and populate GlobalConfig | |F|M|F|1268080236272| F | M | F | 1268080236272 | | cwilper | Update org.fcrepo.server.access.DefaultAccess | |F|M|F|1268080257979| F | M | F | 1268080257979 | | cwilper | Update org.fcrepo.server.access.DynamicAccessModule | |F|M|F|1268080268001| F | M | F | 1268080268001 | | cwilper | Update org.fcrepo.server.journal.Journaler | |F|M|F|1268080276055| F | M | F | 1268080276055 | | cwilper | Update org.fcrepo.server.management.BasicPIDGenerator | |F|M|F|1268080285519| F | M | F | 1268080285519 | | cwilper | Update org.fcrepo.server.management.ManagementModule | |F|M|F|1268080327906| F | M | F | 1268080327906 | | cwilper | Update org.fcrepo.server.messaging.MessagingModule | |F|M|F|1268080339553| F | M | F | 1268080339553 | | cwilper | Update org.fcrepo.server.oai.FedoraOAIProviderModule | |F|M|F|1268080350944| F | M | F | 1268080350944 | | cwilper | Update org.fcrepo.server.resourceIndex.ResourceIndexModule | |F|M|F|1268080374403| F | M | F | 1268080374403 | | cwilper | Update org.fcrepo.server.search.FieldSearchSQLModule | |F|M|F|1268080381223| F | M | F | 1268080381223 | | cwilper | Update org.fcrepo.server.security.DefaultAuthorization | |F|M|F|1268080399963| F | M | F | 1268080399963 | | cwilper | Update org.fcrepo.server.security.DefaultBackendSecurity | |F|M|F|1268080425721| F | M | F | 1268080425721 | | cwilper | Update org.fcrepo.server.storage.ConnectionPoolManagerImpl | |F|M|F|1268080433280| F | M | F | 1268080433280 | | cwilper | Update org.fcrepo.server.storage.DefaultDOManager | |F|M|F|1268080461067| F | M | F | 1268080461067 | | cwilper | Update org.fcrepo.server.storage.DefaultExternalContentManager | |F|M|F|1268082094738| F | M | F | 1268082094738 | | cwilper | Update org.fcrepo.server.storage.lowlevel.akubra.AkubraLowlevelStorageModule | |F| M|F|1268082154104| | M | F | 1268082154104 | | cwilper |nigel thomas|Update org.fcrepo.server.storage.lowlevel.DefaultLowlevelStorageModule | | F | M | F | 1268082165864 | | cwilper | F|M|F|1268082165864| |cwilper|Update org.fcrepo.server.storage.translation.DOTranslationModule | |F|M|F|1268082180490| F | M | F | 1268082180490 | | cwilper | Update org.fcrepo.server.validation.DOValidatorModule |
Phase II - Swap
- Decide on DI framework: Spring 3
- Convert fcfg to DI configuration and update installer to populate it instead
- Trigger initialization of module singletons via DI framework in context initialization
- Use injected module dependencies wherever possible, avoiding use of Module and Server at runtime
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