IS-Publisher

In conjunction with the IS-Client and the IS-Notifier, the IS-Publisher represents the mediation layer gCube Services will rely on to interact with the Information Service as a whole.

Design and Role

The IS-Publisher is a Java library providing a reference implementation for two interfaces (ISPublisher and ISLocaLPublisher) defined in the gCore Framework. The purpose of these interface is to define the behavior of providers of information to the the Information System.

More specifically:

• by implementing the ISPublisher interface, the library allows gCube services to publish two classes of information:

• GCUBEResources
• services' states as of WS-ResourceProperty documents

• by implementing the ISLocalPublisher interface, it provides a subscription/notification mechanism based on local events allowing consumers to be notified about changes in any GCUBEResource published by others within the same GHN. This mechanism is widely exploited by the IS services whenever they are themselves hosted on the local GHN.

At runtime, both the interfaces are dynamically bound to the implementation provided by the library.

ISPublisher Interface

Managing a GCUBEResource

In order to manage a GCUBEResource profile the IS-Publisher interacts with the IS-Registry service in the publishing scope by invoking its appropriate operations.

Publishing a GCUBEResource

The registerGCUBEResource operation has to be invoked to publish a profile in the IS. The operation takes the following parameters as input:

• the resource to publish, an instance of a sub-class of the GCUBEResource class
• the operational scope, an object representing a scope in the gCube model of VO/VREs
• the security manager, the component keeping track of credentials, and returns a string containing the registered profile if the registration is successful.

Here it is an example of GCUBEResource registration:

try {
	ISPublisher publisher = GHNContext.getImplementation(ISPublisher.class); //dynamically load the reference implementation of the interface
	GCUBEGenericResource resource = GHNContext.getImplementation(GCUBEGenericResource.class);
        //invoke setters on the resource here...
	publisher.registerGCUBEResource(resource, this.scope, ServiceContext.getContext());
} catch (Exception e) {			
	logger.error(e);
	throw new Exception("Unable to register the Resource");
}

Updating a GCUBEResource

The updateGCUBEResource operation has to be invoked to update a profile in the IS. The operation takes the following parameters as input:

• the resource to update, an instance of a sub-class of the GCUBEResource class
• the operational scope, an object representing a scope in the gCube model of VO/VREs
• the security manager, the component keeping track of credentials, and returns a string containing the registered profile if the registration is successful.

Here it is an example of GCUBEResource update:

try {
	ISPublisher publisher = GHNContext.getImplementation(ISPublisher.class); //dynamically load the reference implementation of the interface
	GCUBEGenericResource resource = GHNContext.getImplementation(GCUBEGenericResource.class);
        //invoke setters on the resource here...
	publisher.updateGCUBEResource(resource, this.scope, ServiceContext.getContext());
} catch (Exception e) {			
	logger.error(e);
	throw new Exception("Unable to register the Resource");
}

Removing a GCUBEResource

The removeGCUBEResource operation has to be invoked to update a profile in the IS. The operation takes the following parameters as input:

• the resource ID, the unique identifier of the resource to delete
• the resource type, the type of the resource to delete
• the operational scope, an object representing a scope in the gCube model of VO/VREs
• the security manager, the component keeping track of credentials, and returns a string containing the registered profile if the registration is successful.

Here it is an example of GCUBEResource removal:

try {
	ISPublisher publisher = GHNContext.getImplementation(ISPublisher.class); //dynamically load the reference implementation of the interface
	GCUBEGenericResource resource = ....;// the resource could be obtained as a results of a query or passed as input by someone else...
	publisher.removeGCUBEResource(resource.getID(), resource.getType() this.scope, ServiceContext.getContext());
} catch (Exception e) {			
	logger.error(e);
	throw new Exception("Unable to register the Resource");
}

Publishing a service's state

Services' states are represented by a view on the stateful resources data of each service. Such a view is then defined as a WS-ResourceProperty document. The IS-Publisher takes as input the whole GCUBE stateful resource and it is able to extract from there its state and publish it. The following operations allow to publish and unpublish a state:

• registerWSResource() – which takes as input parameter a message containing a stateful resource (each stateful entity different from a gCube Resource) and optionally the registration name and the scope and register such a resource in the IS;
• removeWSResource() – which takes as input parameter a message containing a stateful resource (each stateful entity different from a gCube Resource) and optionally the registration name and the scope and removes such a resource.

The update of the state is automatically performed by the underlying framework as explained in the implementation section.

Subscribing for local events

• subscribeLocalProfileEvents(LocalProfileConsumer consumer) - it subscribes a new consumer as listener of local event. A consumer is an instance of a class extending the LocalProfileConsumer class also defined in the interface. The following methods of the class can be overridden to receive the appropriate callbacks after a modification on any of the local profiles occurred:
  • protected void onProfileRemoved(String resourceID, String type, GCUBEScope scope) - removed profile event callback
  • protected void onProfileUpdated(GCUBEResource resource, GCUBEScope scope) - updated profile event callback.
  • protected void onProfileRegistered(GCUBEResource resource, GCUBEScope scope) - new registered profile event callback.

• isEnabled(GCUBEScope scope) - it checks if in the given scope, the notification mechanism based on local events is enabled or not.

Implementation

The java library implementing the ISPublisher interface has a two-fold role:

• starting from a registerWSResource() invocation, it creates an Aggregator Source and registers it to an Aggregator Sink hosted by a IS-IC instance

• it is mere mediator between the method invocations and the IS-IC and IS-Registry services' stubs for all the other methods exposed by the interface

Through the facilities offered by gCore, the ISPublisher implementation is dynamically bound at runtime any time it is needed with the following line of code:

ISLocalPublisher pubblisher = GHNContext.getImplementation(ISLocalPublisher.class);

ISLocalPublisher Interface

Registration to Local Events

The following example shows how to register a consumer and be notified for local events occurring in the hosting node:

import org.gcube.common.core.informationsystem.publisher.ISLocalPublisher.LocalProfileConsumer;
 
 
private void subscribeToLocalRegistrationEvents() throws Exception{
	ISLocalPublisher pub = GHNContext.getImplementation(ISLocalPublisher.class);
	LocalProfileConsumer cons = new LocalProfileConsumer() {
 
	        /* (non-Javadoc)
	         * @see org.gcube.common.core.informationsystem.publisher.ISLocalPublisher.LocalProfileConsumer#onProfileRegistered(org.gcube.common.core.resources.GCUBEResource)
	         */
	        @Override
	        protected void onProfileRegistered(GCUBEResource resource, GCUBEScope scope) {
	            logger.debug("onProfileRegistered event received" );                                   
	            //manage the event...
 
	        }
 
	        /* (non-Javadoc)
	         * @see org.gcube.common.core.informationsystem.publisher.ISLocalPublisher.LocalProfileConsumer#onProfileRemoved(java.lang.String, java.lang.String)
	         */
	        @Override
	        protected void onProfileRemoved(String resourceID, String type, GCUBEScope scope) {
	            logger.trace("onProfileRemoved event received");
	            //manage the event...	        		                               
	        }
 
	        /* (non-Javadoc)
	         * @see org.gcube.common.core.informationsystem.publisher.ISLocalPublisher.LocalProfileConsumer#onProfileUpdated(org.gcube.common.core.resources.GCUBEResource)
	         */
	        @Override
	        protected void onProfileUpdated(GCUBEResource resource, GCUBEScope scope) {
	            logger.trace("onProfileUpdated event received");
	            //manage the event...	        		                               
	        }
 
 
	    };
 
    pub.subscribeLocalProfileEvents(cons);
}