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.

DSpace Service Manager

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 

The DSpace Services Framework is a backporting 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.

An OSGi service is a java object instance, registered into an OSGi framework with a set of properties. Any java object can be registered as a service, but typically it implements a well-known interface.

represents a "best practice" for new DSpace architecture and implementation of extensions to the DSpace application. DSpace Services are best described as a "Simple Registry" where plugins FIXME. The DS2 (DSpace 2.0) core services are the main services that make up a DS2 system. These includes services for 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).

Core Services

Configuration Service

ConfigurationService cs = new DSpace().getConfigurationService();
String prop = cs.getProperty("property");

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

ConfigurationService cs = new DSpace().getConfigurationService();
String prop = cs.getProperty("prefix.property");

ConfigurationService cs = new DSpace().getConfigurationService();
String prop = cs.getProperty("prefix.property");

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

|

Mirrors DSpace Configuration
dspace/config/dspace.cfg
dspace/config/modules/addon.cfg
Defaults supported in Addon Jars.
addon.jar/spring/

Test Driven Development

Test-driven development (TDD) 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

We want to clarify that that the Testing Framework in the DSpace Services Module Predated the actual JUnit testing support that was added to dspace-api.  Testing is a very beneficial practice where the developer writes small java based test of the code they are going to produce.  The 

Test-driven development is related to the test-first programming concepts of extreme programming, begun in 1999,[[2]|http://en.wikipedia.org/wiki/Test-driven_development#cite_note-Cworld92-1] but more recently has created more general interest in its own right.[[3]|http://en.wikipedia.org/wiki/Test-driven_development#cite_note-Newkirk-2]

ACCESSING REGISTERED SERVICES

DEFINING SERVICES
SPRING CONFIGURATION
PROTOTYPES VS SINGLETONS
Example: Creating a Comments Service
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The IMPLEMENTATION
TEST DRIVEN DEVELOPMENT

Using the Service Manager Testing Framework

DSpaceAbstractRequestTest

This is an abstract class which makes it easier to test execution of your service within a DSpace "Request Cycle" and includes an automatic request wrapper around every test method which will start and end a request, the default behavior is to end the request with a failure which causes a rollback and reverts the storage to the previous values

public abstract class DSpaceAbstractRequestTest extends DSpaceAbstractKernelTest {

    /**
     * @return the current request ID for the current running request
     */
    public String getRequestId() {
        return requestId;
    }

    @BeforeClass
    public static void initRequestService() {
        _initializeRequestService();
    }

    @Before
    public void startRequest() {
        _startRequest();
    }

    @After
    public void endRequest() {
        _endRequest();
    }

    @AfterClass
    public static void cleanupRequestService() {
        _destroyRequestService();
    }

}

DSpaceAbstractKernelTest

This is an abstract class which makes it easier to test things that use the DSpace Kernel, this will start and stop the kernel at the beginning of the group of tests that are in the junit test class which extends this

public abstract class DSpaceAbstractKernelTest extends DSpaceAbstractTest {

    @BeforeClass
    public static void initKernel() {
        _initializeKernel();
        assertNotNull(kernelImpl);
        assertTrue(kernelImpl.isRunning());
        assertNotNull(kernel);
    }

    @AfterClass
    public static void destroyKernel() {
        _destroyKernel();
    }

    /**
     * Test method for {@link org.dspace.kernel.DSpaceKernelManager#getKernel()}.
     */
    @Test
    public void testKernelIsInitializedAndWorking() {
        assertNotNull(kernel);
        assertTrue(kernel.isRunning());
        DSpaceKernel k2 = new DSpaceKernelManager().getKernel();
        assertNotNull(k2);
        assertEquals(kernel, k2);
    }

}

DEFINING AN IN-MEMORY DATABASE
API
Defining the API of the SERVICE
The DATABASE IMPLEMENTATION
Defining the SERVICE in SPRING
THE SERVICE MANAGER
THE SPRING CONFIG

The XMLUI OVERLAY
AspectS
Consectetuer arcu ipsum ornare pellentesque vehicula, in vehicula diam, ornare magna erat felis wisi a risus. Justo fermentum id.
THEME RESOURCES
Developing with DSpace
Architectural Introduction
Maven Archetype
Project Generation
Maven Module Wiring
Dependencies
Tiers
Persisitence
Business
Application
Tools
Maven
Jar Projects
Dependencies
Inheritance
modularity
War Projects
overlays
modularity
Spring
ServiceManager
Core Services
ConfigurationService
Configuration via Spring vs. ConfigurationService
DatabaseService
Opening Doors to Persistence Frameworks
DAO Repositories
Defining, Replacing and Augmenting Storage
Whats a Service?
Defining and Replacing Business Services
Creating Your Own Services
Webapplications
XMLUI / Cocoon
JSPUI (WebMVC)
Example
Facebook Authentication for DSpace
Spring Security
OAuth 2.0 for Spring Security
Facebook Authentication
Implementation
Spring Security Authenticator
Authentication Service

Architectural Overview

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.

Kernel registration

The kernel will automatically register itself as an MBean when it starts up so that it can be managed via JMX. It allows startup and shutdown and provides direct access to the ServiceManager and the ConfigurationService. All the other core services can be retrieved from the ServiceManager by their APIs.

Service Manager

The ServiceManager abstracts the concepts of service lookups and lifecycle control. It also manages the configuration of services by allowing properties to be pushed into the services as they start up (mostly from the ConfigurationService). The ServiceManagerSystem abstraction allows the DSpace ServiceManager to use different systems to manage its services. The current implementations include Spring and Guice. This allows DSpace 2 to have very little service management code but still be flexible and not tied to specific technology. Developers who are comfortable with those technologies can consume the services from a parent Spring ApplicationContext or a parent Guice Module. The abstraction also means that we can replace Spring/Guice or add other dependency injection systems later without requiring developers to change their code. The interface provides simple methods for looking up services by interface type for developers who do not want to have to use or learn a dependency injection system or are using one which is not currently supported.

The DS2 kernel is compact so it can be completely started up in a unit test (technically integration test) environment. (This is how we test the kernel and core services currently). This allows developers to execute code against a fully functional kernel while developing and then deploy their code with high confidence.

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.

Access to the kernel is provided via the Kernel Manager through the DSpace object, which will locate the kernel object and allow it to be used.

Standalone Applications

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 = dspace.getEventService();

The DSpace launcher (

bin/dspace

) initializes a kernel before dispatching to the selected command.

Application Frameworks (Spring, Guice, etc.)

Similar to Standalone Applications, but you can use your framework to instantiate an org.dspace.utils.DSpace object.

    <bean id="dspace" class="org.dspace.utils.DSpace"/>

Web Applications

In web applications, the kernel can be started and accessed through the use of Servlet Filter/ContextListeners which are provided as part of the DSpace 2 utilities. Developers don't need to understand what is going on behind the scenes and can simply write their applications and package them as webapps and take advantage of the services which are offered by DSpace 2.

Providers and Plugins

For developers (how we are trying to make your lives easier): The DS2 ServiceManager supports a plugin/provider system which is runtime hot-swappable. The implementor can register any service/provider bean or class with the DS2 kernel ServiceManager. The ServiceManager will manage the lifecycle of beans (if desired) and will instantiate and manage the lifecycle of any classes it is given. 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 service if desired. The goal of this system is to allow DS2 to be extended without requiring any changes to the core codebase or a rebuild of the code code.

Activators

Developers can provide an activator to allow the system to startup their service or provider. It is a simple interface with 2 methods which are called by the ServiceManager to startup the provider(s) and later to shut them down. These simply allow a developer to run some arbitrary code in order to create and register services if desired. It is the method provided to add plugins directly to the system via configuration as the activators are just listed in the configuration file and the system starts them up in the order it finds them.

Provider Stacks

Utilities are provided to assist with stacking and ordering providers. Ordering is handled via a priority number such that 1 is the highest priority and something like 10 would be lower. 0 indicates that priority is not important for this service and can be used to ensure the provider is placed at or near the end without having to set some arbitrarily high number.

Core Services

The core services are all behind APIs so that they can be reimplemented without affecting developers who are using the services. Most of the services have plugin/provider points so that customizations can be added into the system without touching the core services code. For example, let's say a deployer has a 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.

Caching Service

Provides for a centralized way to handle caching in the system and thus a single point for configuration and control over all caches in the system. Provider and plugin developers are strongly encouraged to use this rather than implementing their own caching. The caching service has the concept of scopes so even storing data in maps or lists is discouraged unless there are good reasons to do so.

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:

1.) Type Casting and Array Parsing: Configuration Service will slip your comma separated values for you.

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

Use commas for lists of values, use lookups

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

wiring your default configuuration

overriding defaults

EventService

Handles events and provides access to listeners for consumption of events.

RequestService

In DS2 a request is an atomic transaction in the system. It is likely to be an HTTP request in many cases but it does not have to be. This service provides the core services with a way to manage atomic transactions so that when a request comes in which requires multiple things to happen they can either all succeed or all fail without each service attempting to manage this independently. In a nutshell this simply allows identification of the current request and the ability to discover if it succeeded or failed when it ends. Nothing in the system will enforce usage of the service, but we encourage developers who are interacting with the system to make use of this service so they know if the request they are participating in with has succeeded or failed and can take appropriate actions.

SessionService

In DS2 a session is like an HttpSession (and generally is actually one) so this service is here to allow developers to find information about the current session and to access information in it. The session identifies the current user (if authenticated) so it also serves as a way to track user sessions. Since we use HttpSession directly it is easy to mirror sessions across multiple servers in order to allow for no-interruption failover for users when servers go offline.

Examples

Configuring Event Listeners

Event Listeners can be created by overriding the the EventListener interface:

In Spring:

<?xml version="1.0" encoding="UTF-8"?>
<beans>

    <bean id="dspace" class="org.dspace.utils.DSpace"/>

    <bean id="dspace.eventService"
          factory-bean="dspace"
          factory-method="getEventService"/>

    <bean class="org.my.EventListener">
         <property name="eventService" >
    		<ref bean="dspace.eventService"/>
    	</property>
    </bean>
</beans>

(org.my.EventListener will need to register itself with the EventService, for which it is passed a reference to that service via the eventService property.)

or in Java:

DSpace dspace = new DSpace();

EventService eventService = dspace.getEventService();

EventListener listener = new org.my.EventListener();
eventService.registerEventListener(listener);

(This registers the listener externally – the listener code assumes it is registered.)

TODO: examples in Guice

TODO: examples of implementing and registering configurations in Spring and Guice

TBS: how we did X before : how we do it using the Framework

Recommendations for DSpace 2.0