DSpace Service Manager Tutorial

Introduction

The objectives of this tutorial are to provide the general DSpace Developer with an understanding of what the DSpace Service Manager is and what we are attempting to attain through its usage and some basic software development practices and design principles.  The tutorial will break these practices and the overall development platform down into developer centric terms that should, if successful, give the developer a reference for how to best design their code.  Goals of the Service Manager are to assist in separating the dependencies of individual functional areas of DSpace on one another, by eliminating significant dependencies on other parts of the codebase and the prevalence of "StaticManager" Classes.

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Caveat: It is clear that Spring has become quite dominant a solution in DSpace with the adoption of Apache Cocoon 2.2 for the Manakin XMLUI and Spring MVC for the Freemarker Prototype Webapplication currently under Development.  Spring is even being considered for use in the

Allows for non-specific access to the core services. No dependency on the underlying mechanism is exposed. Allows the developer to register and lookup references to desired Service Objects Objects

The DSpace Application Lifecycle

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When a request is made by either the Webapplication or the CLI initialization, then the Request Lifecycle is engaged:

DSpace Kernel

The DSpace Kernel manages the start up and access services in the DSpace Services framework. It is meant to allow for a simple way to control the core parts of DSpace and allow for flexible ways to startup the kernel. For example, the kernel can be run inside a single webapp along with a frontend piece (like JSPUI) or it can be started as part of the servlet container so that multiple webapps can use a single kernel (this increases speed and efficiency). The kernel is also designed to happily allow multiple kernels to run in a single servlet container using identifier keys.

Basic Usage

To use the Framework you must begin by instantiating and starting a DSpaceKernel. The kernel will give you references to the ServiceManager and the ConfigurationService. The ServiceManager can be used to get references to other services and to register services which are not part of the core set. For  For standalone applications, access to the kernel is provided via the Kernel Manager and the DSpace object which will locate the kernel object and allow it to be used.

/* 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();

The DSpace launcher (

bin/dspace

) initializes a kernel before dispatching to the selected command.

The Service Manager Interface

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Example, specialized authentication system and wants to manage the authentication calls which come into the system. The implementor can simply implement an AuthenticationProvider and then register it with the DS2 kernel's ServiceManager. This can be done at any time and does not have to be done during Kernel startup. This allows providers to be swapped out at runtime without disrupting the DS2 service if desired. It can also speed up development by allowing quick hot redeploys of code during development.

Configuration Service

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 2.

Manages the configuration of the DSpace 2 system. Can be used to manage configuration for providers and plugins also.

Benefits over the DSpace ConfigurationManager

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• Type Casting: Common Configuration Interface supports type casting of configuration values of the type required by the caller.
• Array Parsing: As part of this type casting, the Configuration Service will split your comma separated values for you

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Recommendations: Why parse values if you do not have to, avoid Parsing Values where-ever possible.

• Use commas for lists of values, use lookups

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• (If you end up thinking you want to create maps in your properties, your doing it in the wrong place look instead at Spring Configuration and objectifying your configuration)
• Objectifying Configuration

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wiring your default configuuration

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• (Its best to wire your application components with Spring).

Acquiring the Configuration Service

/* Instantiate the Utility Class */
DSpace dspace = new DSpace();

/* Access get the Service Manager by convenience method */
ConfigurationService service = dspace.getSingletonService(ConfigurationService.class);

Legacy Configuration

_\[dspace\]/config/dspace.cfg

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ConfigurationService contributed to DSpace 1.7.1 (Service Manager Version 2.0.3) 
support for reading the same "dspace.cfg" legacy file is supported. Example of Usage:
ConfigurationService cs = new DSpace().getConfigurationService();
String prop = cs.getProperty("property");

String prop = ConfigurationManager.getProperty("property");

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