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The DSpace Services Framework is a back-porting of the DSpace 2.0 Development Group's work in creating a reasonable and simple "Core Services" layer for DSpace. The Services Framework provides a means for application developers to both lookup and register their own "services" or JAVA objects that can be referred to by the application.
What are services?
Answer: services are a generic term for the business actions that provide functionality that will complete a specific task in the application.
In DSpace Services are conceptually similar to OSGi Services , where an addon library (a OSGi Bundle) delivers a singleton instance of a class as a service for other application code to utilize. In OSGi the Service often has a Java Interface class and constitutes a "Contract" for the application.
From a Design Standpoint, The Service Manager is a Service Locator Pattern. This shift represents a "best practice" for new DSpace architecture and the implementation of extensions to the DSpace application. DSpace Services are best described as a "Registry" of Services that are delivered to the application for use by the use of a Spring Application Context. The original (DSpace 2.0 ) core services are the main services that make up a DSpace Service Manager system. These include services for the application "Configuration", "Transactional Context", "Requests" and user "Session", "Persistence" things like user and permissions management and storage and caching. These services can be used by any developer writing DS2 plugins (e.g. statistics), providers (e.g. authentication), or user interfaces (e.g. JSPUI).
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ApplicationContext context = new ClassPathXmlApplicationContext(
new String[] {"example.xml"});
Example myExample = applicationContext.getBean("my-example");
/* Go on to do something interesting with the service */
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The Case For Spring
This tutorial focuses on adoption of Spring as a best practice for many aspects of DSpace development, from Core Library definition and instantiation to Application Developer implementation of customizations and addons.
- Spring focuses around providing a way to manage your business objects. (DSpace currently lacks this capability).
- Spring is both comprehensive and modular. Spring has a layered architecture, you can choose to use just about any part of it in isolation.
- It is easy to introduce Spring incrementally into existing projects. (The Latest DSpace WebMVC, REST and XMLUI development efforts already leverage Spring WebMVC in the application tier).
- Spring is designed from the ground up to help you write code that's easy to test. Spring is an ideal framework for test driven projects. (DSpace has only just introduced a JUnit Test Suite, which does not leverage Spring in its solution. However, the DSpace Service Manager already delivers a testing suite leverages Spring to support testing configuration).
- Spring is an increasingly important integration technology, its role recognized by several large vendors. By utilizing Spring, DSpace will be able to incrementally improve its architecture to be more robust, and more "enterprise grade".
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<bean class="org.dspace.MyService" autowire="byType"/>
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Spring AutoWiring looks for other bean of our specific type elsewhere in our configuration and injects them into our service. This is the basic mechanism whereby Addon Modules can reuse existing services or even services provided by other third party modules without having to explicitly depend on any specific implementation of those services.
The DSpace Application Lifecycle
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/* Instantiate the Utility Class */ DSpace dspace = new DSpace(); /* Access get the Service Manager by convenience method */ ServiceManager manager = dspace.getServiceManager(); /* Or access by convenience method for core services */ EventService service = manager.getServiceBydspace.getEventService(); |
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The Service Manager Interface
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Core Services
Configuration Service
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ConfigurationService contributed to DSpace 1.7.1 (Service Manager Version 2.0.3) And maintains Parity with the existing DSpace ConfigurationManager in supporting "dspace.cfg" and modular "config/modules/\[module\].cfg" configuration.
The ConfigurationService controls the external and internal configuration of DSpace 2. It reads Properties files when the kernel starts up and merges them with any dynamic configuration data which is available from the services. This service allows settings to be updated as the system is running, and also defines listeners which allow services to know when their configuration settings have changed and take action if desired. It is the central point to access and manage all the configuration settings in DSpace.
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Modular Default Configuration
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_\[addon.jar\]/config/\[service\].cfg _cfg
Any service can provide sane defaults in a java properties configuration file. These properties will be able to be looked up directly using a prefix as syntax.
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Modularization of Configuration Not Bound to API signature.
Wiki Markup
Any service can provide overrides in the DSpace home configuration directory sane defaults in a java properties configuration file. These properties will be able to be looked up directly using a prefix as syntax.
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Similar to the Context Service, The DSpace Legacy DataSource Service is part of the Domain Model refactoring work and bring the preexisting DSpace DataSource instantiated within the the DSpace DatabaseManager into the Spring Application Context. The exposure of the DataSource will enable Service Beans in the DSpace ServiceManager to utilize popular tools for ORM such as Hibernate, JPA2, ibatis, Spring Templates, or your own custom persistence support to be used when developing your Services for DSpace.
Test Driven Development
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{*}Test-driven development* (*TDD*) is a [software development process|http://en.wikipedia.org/wiki/Software_development_process] that relies on the repetition of a very short development cycle: first the developer writes a failing automated [test case|http://en.wikipedia.org/wiki/Test_case] that defines a desired improvement or new function, then produces code to pass that test and finally [refactors|http://en.wikipedia.org/wiki/Code_refactoring] the new code to acceptable standards. [Kent Beck|http://en.wikipedia.org/wiki/Kent_Beck], who is credited with having developed or 'rediscovered' the technique, stated in 2003 that TDD encourages simple designs and inspires confidence.\is a software development process that relies on the repetition of a very short development cycle: first the developer writes a failing automated test case that defines a desired improvement or new function, then produces code to pass that test and finally refactors the new code to acceptable standards. Kent Beck, who is credited with having developed or 'rediscovered' the technique, stated in 2003 that TDD encourages simple designs and inspires confidence.[http://en.wikipedia.org/wiki/Test-driven_development\]
http://en.wikipedia.org/wiki/Test-driven_development#cite_note-Beck-0
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