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.

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).

What is OSGi?

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. Considerable has evolved in both the Spring and OSGi Communities.

What is Spring?

Spring is an Inversion of Control (IoC) container that utilizes Dependency Injection (a fancy way of just saying that Spring creates and hands the JAVA objects you would normally have had to create in your code).

Example of Not Using Spring

As a brief example Here is a class that does not use Dependency Injection, it calls "new SomeOtherClass()" directly in its constructor.

public class Example {

    private SomeOtherClass myObject = null;

    public Example(){
        myObject = new SomeOtherClass();
    }
}

Example Using Spring

Here is an example of a better coding practice, where we give up the responsibility for the creation of the class and allow the IoC/DI container to be responsible for its creation.

public class Example {

    private SomeOtherClass myObject = null;

    public Example(SomeOtherClass object){
        this.myObject = object;
    }
}

This immediately opens the door for "SomeOtherClass" to be changed out with new/other subclasses of "SomeOtherClass". In Spring, the definition "example.xml" file might look like this:

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

    <bean id="someObject" class="com.example.SomeOtherClass"/>

    <bean id="ny-example" class="com.example.Example">
        <constructor-arg ref="someObject"/>
    </bean>

</beans>

Where, when the ServiceManager is started, two beans are instantiated by Spring, and one is used in the constructor argument of the other. The simplest instantiation of a Spring Container might look like the following.

ApplicationContext context = new ClassPathXmlApplicationContext(
        new String[] {"example.xml"});
Example myExample = applicationContext.getBean("my-example");

/* Go on to do something interesting with the service */

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".

The Service Manager

The ServiceManager provides the DSpace Application with the above Spring ApplicationContext so that the developer does not need to be responsible for its creation when developing against DSpace. Thus, to extend the pervious example, the DSpace class and its underlying Service Manager can be utilized to get at any object that has been instantiated as a service bean by core or addon application code.Example example = new DSpace().getSingletonService("my-example", Example.class);
/* Go on to do something interesting with the service */

The DSpace Service Manager implementation manages the entire lifecycle of a running DSpace application and provides access to services by Applications that may be executing external to this "kernel" of DSpace Services. Via Spring and loading of individual dspace.cfg properties the ServiceManager manages the configuration of those services, (either through providing those properties to the Spring Application Context where they can be injected in Spring definition xml files and/or "annotations" or by exposing those properties via the injection of the DSpace ConfigurationService.

DSpace ConfigurationService

The ServiceManagerSystem abstraction allows the DSpace ServiceManager to use different systems to manage its services. The current implementation is Spring Framework based. The original design intent of the Service Manager was to support more than one IoC/DI Solution, however, as work has progressed with DSpace, it has become clear that there are trade offs to consider in its usage.

Spring Injection, when used properly, means we do not reallyneed to make "lookup calls" to a central "ServiceManager" or "DSpace" object to acquire the service beans we our own code to work with.
Fewer lookups mean less centralized dependencies
Fewer Centralized Dependencies means fewer bottlenecks in source Code Dependency Management.
Fewer Bottlenecks means greater modularity and encapsulation, less need to carry around all the source code when overriding and customizing "dspace".
More use of binary distributions means greater ease in upgrading DSpace.

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 in the community.

This leads us to our first best practice:

Best Practice 1: If possible, do use Dependency Injection to acquire your services. This will be of benefit down the road if we make changes to the service manager architecture.

In creating classes that work within the system, the ServiceManager will inject those services you need for you.

public class Example {

    ConfigurationService configurationService;

    RequestService requestService;

    public Example(ConfigurationService cs, RequestService rs)
    {
        this.configurationService = cs;
        this.requestService = rs;
    }

}

Where in our spring configuration we would register this Service via the following configuration:

    <bean class="org.dspace.MyService" autowire="byType"/>

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

The life cycle of the container and the services therein is controlled by the Web-application context or the DSpace CLI ScriptLauncher main executable in which the servlet has been deployed. The Lifecycle assures that when the Service managers (and specifically Spring in this case) are initialized, the required core and addon services are wired and made available to your application.

The ServiceManager Request Cycle

The ServiceManager Request Cycle is similar to the Webapplication Request Cycle. In the case of the Service Request, There is an incoming "Request" object with the state of the a call from the client, this Request is then enterpreted by the Container and mapped to a specific Servlet, which executes to completion, On Completion, the Serlvet Generates a

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

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 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

public interface ServiceManager {

    /**
     * Allows developers to get the desired service singleton by the provided type.
     * This should return all instantiated objects of the type specified
     * (may not all be singletons).
     *
     * @param <T>
     * @param type the type for the requested service (this will typically be the interface class but can be concrete as well)
     * @return the list of service singletons OR empty list if none is found
     */
    public <T> List<T> getServicesByType(Class<T> type);

    /**
     * Allows developers to get the desired service singleton by the provided name and type.
     * Provide {@code null} for the name if it is not known, but it is better to ensure it is set.
     * <p>
     * <em>NOTE</em>: This also allows special access to the underlying
     * service manager objects.  It is possible to get the underlying Spring ApplicationContext object like so:
     * <xmp>
     * getServiceByName(ApplicationContext.class.getName(), ApplicationContext.class);
     * </xmp>
     *
     * @param <T>
     * @param name (optional) the unique name for this service.
     * If null then the bean will be returned if there is only one
     * service of this type.
     * @param type the type for the requested service (this will typically be the interface class but can be concrete as well)
     * @return the service singleton OR null if none is found
     */
    public <T> T getServiceByName(String name, Class<T> type);

    /**
     * Lookup to see if a service exists with the given name.
     *
     * @param name the unique name for this service
     * @return true if it exists, false otherwise
     */
    public boolean isServiceExists(String name);

    /**
     * Get the names of all registered service singletons.  By
     * convention, the name typically matches the fully qualified class
     * name).
     *
     * @return the list of all current registered services
     */
    public List<String> getServicesNames();

    /**
     * Allows adding singleton services and providers in at runtime or
     * after the service manager has started up.
     * This is primarily useful for registering providers, filters, and
     * plugins with the DSpace core.
     *
     * @param name the name of the service (must be unique)
     * @param service the object to register as a singleton service
     * @throws IllegalArgumentException if the service cannot be registered
     */
    public void registerService(String name, Object service);

    /**
     * Allows adding singleton services and providers in at runtime or
     * after the service manager has started up.
     * This is the same as {@link #registerService(String, Object)}
     * except that it allows the core service manager to startup your
     * service for you instead of you providing a service to the core.
     * In general, it is better if you use your own service manager
     * (like Spring or Guice) to manage your services  and simply
     * inherit the core service beans from the DSpace core service
     * manager using the special capabilities of
     * {@link #getServiceByName(String, Class)}.
     *
     * @see ServiceManager#getServiceByName(String, Class)
     * @param name the name of the service (must be unique)
     * @param type the class type of the service (must be in the current classloader)
     * @throws IllegalArgumentException if the service cannot be registered because the name is taken or type is invalid or other
     */
    public <T> T registerServiceClass(String name, Class<T> type);

    /**
     * Allows a service to be unregistered (which will only work if
     * nothing depends on it).
     * This is primarily used for providers, filters, plugins, etc.
     * which were registered but are no longer available because the
     * context they are running in is shutting down or restarting.
     * <br/>
     * WARNING: This should not be used to attempt to unregister core
     * services as that will fail.
     *
     * @param name the name of the service (must be unique)
     * @throws IllegalArgumentException if the bean cannot be unregistered
     */
    public void unregisterService(String name);

    /**
     * Allows new configuration settings to be pushed into the core
     * DSpace configuration.
     * These will cause a settings refresh action to be called for all
     * services which are listening and will cause any bean properties
     * to be pushed into existing beans.
     *
     * @param settings a map of keys (names) and values
     */
    public void pushConfig(Map<String, String> settings);

}

Core Services

Request Service

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 DSpace 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.

public interface Request {

    public String getRequestId();

    public Session getSession();

    public Object getAttribute(String name);

    public void setAttribute(String name, Object o);

    public ServletRequest getServletRequest();

    public HttpServletRequest getHttpServletRequest();

    public ServletResponse getServletResponse();

    public HttpServletResponse getHttpServletResponse();

}

The DSpace Session

The Session represents a user's session (login session) in the system. Can hold some additional attributes as needed, but the underlying implementation may limit the number and size of attributes to ensure session replication is not impacted negatively. A DSpace 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.

public interface Session extends HttpSession {

    /**
     * @return the session identifier.  This is not the {@link #getId()}
     * from HttpSession unless no session id was specified when the
     * session was bound.
     */
    public String getSessionId();

    /**
     * Return the internal user ID for this session.
     *
     * @return internal user ID for the user using this session.
     * This is null if the session is anonymous.
     */
    public String getUserId();

    /**
     * Get the external/enterprise user ID for this session.
     *
     * @return the external/enterprise user id of the user associated with this session
     */
    public String getUserEID();

    /**
     * @return true if this session is active OR false if the session has timed out or been invalidated
     */
    public boolean isActive();

    /**
     * @return id of the server with which this session is associated.
     */
    public String getServerId();

    /**
     * @return the IP Address from which this session originated
     */
    public String getOriginatingHostIP();

    /**
     * @return the hostname from which this session originated
     */
    public String getOriginatingHostName();

    /**
     * Get an attribute from the session if one exists.
     * @param key  the key for the attribute
     * @return the value if one exists OR null if none
     */
    public String getAttribute(String key);

    /**
     * Set an attribute on a session.
     *
     * @param key for the attribute
     * @param value (if this is null then the attribute is removed)
     */
    public void setAttribute(String key, String value);

    /**
     * Get all attributes of this session.
     * @return a copy of the attributes in this session.
     * Modifying it has no effect on the session attributes.
     */
    public Map<String, String> getAttributes();

    /**
     * Purges all data from this session and effectively resets it to an
     * anonymous session.  Does not invalidate the session, though.
     */
    public void clear();

Benefits over the Legacy DSpace ConfigurationManager

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 comma separated values for you when you request the property as type "Array"

/* type casting */
int value = configurationService.getPropertyAsType("some-integer",int.class);



/* Array Parsing */
String[] values = configurationService.getPropertyAsType("some-array", String[].class);

/* Default Values */
int value = configurationService.getPropertyAsType("some-integer",1);



/* Default Array Values */
String[] values = configurationService.getPropertyAsType("some-array",new String[]{"my", "own", "array"});

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

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.

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.

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

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);

The ConfigurationService API

public interface ConfigurationService {

    /**
     * Get a configuration property (setting) from the system as a
     * specified type.
     *
     * @param <T>
     * @param name the property name
     * @param type the type to return the property as
     * @return the property value OR null if none is found
     * @throws UnsupportedOperationException if the type cannot be converted to the requested type
     */
    public <T> T getPropertyAsType(String name, Class<T> type);

    /**
     * Get a configuration property (setting) from the system, or return
     * a default value if none is found.
     *
     * @param <T>
     * @param name the property name
     * @param defaultValue the value to return if this name is not found
     * @return the property value OR null if none is found
     * @throws IllegalArgumentException if the defaultValue type does not match the type of the property by name
     */
    public <T> T getPropertyAsType(String name, T defaultValue);

    /**
     * Get a configuration property (setting) from the system, or return
     * (and possibly store) a default value if none is found.
     *
     * @param <T>
     * @param name the property name
     * @param defaultValue the value to return if this name is not found
     * @param setDefaultIfNotFound if this is true and the config value
     * is not found then the default value will be set in the
     * configuration store assuming it is not null.  Otherwise the
     * default value is just returned but not set.
     * @return the property value OR null if none is found
     * @throws IllegalArgumentException if the defaultValue type does not match the type of the property by name
     */
    public <T> T getPropertyAsType(String name, T defaultValue, boolean setDefaultIfNotFound);

    /**
     * Get all currently known configuration settings
     *
     * @return all the configuration properties as a map of name -> value
     */
    public Map<String, String> getAllProperties();

    /**
     * Convenience method - get a configuration property (setting) from
     * the system.
     *
     * @param name the property name
     * @return the property value OR null if none is found
     */
    public String getProperty(String name);

    /**
     * Convenience method - get all configuration properties (settings)
     * from the system.
     *
     * @return all the configuration properties in a properties object (name -> value)
     */
    public Properties getProperties();

    /**
     * Set a configuration property (setting) in the system.
     * Type is not important here since conversion happens automatically
     * when properties are requested.
     *
     * @param name the property name
     * @param value the property value (set this to null to clear out the property)
     * @return true if the property is new or changed from the existing value, false if it is the same
     * @throws IllegalArgumentException if the name is null
     * @throws UnsupportedOperationException if the type cannot be converted to something that is understandable by the system as a configuration property value
     */
    public boolean setProperty(String name, Object value);

}

The most important

Legacy Configuration

[dspace]/config/dspace.cfg

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");

Default Configuration

[addon.jar]/config/[service].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.

Example of Usage:

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

N/A

Modularization of Configuration

[dspace]/config/module/[prefix].cfg

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.

Example of Usage:

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

In DSpace 1.7.0 enhanced capabilities were added to the ConfigurationManager to support the separation of of properties into individual files. The name of these files is utilized as a "prefix" to isolate properties that are defined across separate files from colliding.

Example of Usage:

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
Ac dolor ac adipiscing amet bibendum nullam, massa lacus molestie ut libero nec, diam et, pharetra sodales eget, feugiat ullamcorper id tempor eget id vitae. Mauris pretium eget aliquet, lectus tincidunt.
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);
    }

}

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

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.

EventService

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

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.)

Page tree

DSpace Spring Services Tutorial

DSpace Service Manager Tutorial

Introduction

What are services?

What is OSGi?

What is Spring?

Example of Not Using Spring

Example Using Spring

The Case For Spring

The Service Manager

DSpace ConfigurationService

The DSpace Application Lifecycle

The ServiceManager Request Cycle

Basic Usage

The Service Manager Interface

Core Services

Request Service

The DSpace Session

Benefits over the Legacy DSpace ConfigurationManager

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

Configuration Service

Acquiring the Configuration Service

The ConfigurationService API

Legacy Configuration

Default Configuration

Modularization of Configuration

Test Driven Development

Using the Service Manager Testing Framework

DSpaceAbstractRequestTest

DSpaceAbstractKernelTest

Application Frameworks (Spring, Guice, etc.)

Web Applications

Providers and Plugins

Activators

Provider Stacks

Core Services

Caching Service

EventService

Configuring Event Listeners