com.caplin.datasource.publisher

Interface Publisher

All Known Subinterfaces:

ActivePublisher, BroadcastPublisher, CompatibilityPublisher

public interface Publisher

An instance of Publisher publishes messages to remote DataSource peers on behalf of a DataProvider. It also provides access to a MessageFactory that creates the messages to be published.

DataSource for Java includes several implementations of Publisher that you can use in your DataSource application: see BroadcastPublisher, ActivePublisher and CompatibilityPublisher. To use one of these Publishers, call the appropriate "create publisher" method of DataSource:

• DataSource.createActivePublisher(com.caplin.datasource.namespace.Namespace, DataProvider)
• DataSource.createBroadcastPublisher(com.caplin.datasource.namespace.Namespace)
• DataSource.createCompatibilityPublisher(com.caplin.datasource.namespace.Namespace, DataProvider)

These three child interfaces declare no methods further to those declared in Publisher and currently only serve to tag each Publisher type. However, it is possible that future versions of DataSource for Java may add publisher-type specific methods to these interfaces if deemed appropriate or useful.

Creating an active publisher

The following example shows how to create an active publisher:

import com.caplin.datasource.DataSource;
import com.caplin.datasource.namespace.Namespace;
import com.caplin.datasource.namespace.PrefixNamespace;
import com.caplin.datasource.publisher.DataProvider;
import com.caplin.datasource.publisher.DiscardEvent;
import com.caplin.datasource.publisher.Publisher;
import com.caplin.datasource.publisher.RequestEvent;

public class CreateActivePublisherExample
{
        public static void createActivePublisherExample(DataSource dataSource)
        {
                // Create a simple Namespace that matches subjects starting with the "/FX".
                Namespace fxNamespace = new PrefixNamespace("/FX");
                
                // Create a DataProvider to handle requests and discards from clients
                new MyDataProvider(dataSource, fxNamespace);
        }
        
        static class MyDataProvider implements DataProvider
        {
                @SuppressWarnings("unused")
                private final Publisher publisher;
                
                public MyDataProvider(DataSource dataSource, Namespace nameSpace)
                {
                        // Ask the DataSource to create a publisher that uses the fxNameSpace.
                        publisher = dataSource.createActivePublisher(nameSpace, this);
                }
                
                @Override
                public void onRequest(RequestEvent requestEvent)
                {
                        // Respond to client request by publishing data using the publisher.
                }
                
                @Override
                public void onDiscard(DiscardEvent discardEvent)
                {
                        // Respond to client discard by stopping publishing data.
                }
        }
}

Creating a broadcast publisher

The following example shows a Publisher being created by calling the DataSource.createBroadcastPublisher(Namespace) method of the DataSource. Note that no DataProvider is needed for a BroadcastPublisher. This is because the connected peers (to which the broadcast data updates are sent) do not send the DataSource any subscription or discard requests for the broadcast subjects, so no DataProvider is needed to handle such events.

import com.caplin.datasource.DataSource;
import com.caplin.datasource.messaging.record.RecordMessage;
import com.caplin.datasource.namespace.Namespace;
import com.caplin.datasource.namespace.PrefixNamespace;
import com.caplin.datasource.publisher.Publisher;

public class CreateBroadcastPublisherExample
{
        public static void createBroadcastPublisherExample(DataSource dataSource)
        {
                // Create a simple Namespace that matches subjects starting with the "/FX".
                Namespace fxNamespace = new PrefixNamespace("/FX");
                
                // Ask the DataSource to create a publisher that uses the fxNameSpace.
                Publisher publisher = dataSource.createBroadcastPublisher(fxNamespace);
                
                // Create a record message and broadcast it
                RecordMessage message = publisher.getMessageFactory().createRecordType1Message("/FX/GBPUSD");
                message.setField("Bid", "1.5905");
                message.setField("Ask", "1.5920");
                publisher.publishInitialMessage(message);
        }
}

Method Summary

Methods

Modifier and Type	Method and Description
MessageFactory	getMessageFactory() Gets the MessageFactory used to create the messages that are published via this Publisher.
void	publishInitialMessage(Message message) Publishes the initial image of the data for a subject to peers that have just requested (subscribed to) that subject.
void	publishMappingMessage(MappingMessage mappingMessage) Publishes a message that instructs the peer that it should request a different subject and map the updates across.
void	publishSubjectErrorEvent(SubjectErrorEvent subjectErrorEvent) Publishes to all peers subscribed to a subject an event detailing an error in the subscription for that subject.
void	publishSubjectStatusEvent(SubjectStatusEvent subjectStatusEvent) Publishes to all subscribed peers an event about the change in status of a subject.
void	publishToSubscribedPeers(Message message) Publishes a message to subscribed peers (that is, the peers that have already received an initial image).

Method Detail

getMessageFactory

MessageFactory getMessageFactory()

Gets the MessageFactory used to create the messages that are published via this Publisher.

Returns:

The message factory.

publishInitialMessage

void publishInitialMessage(Message message)

Publishes the initial image of the data for a subject to peers that have just requested (subscribed to) that subject.

Parameters:

message - The message.

publishToSubscribedPeers

void publishToSubscribedPeers(Message message)

Publishes a message to subscribed peers (that is, the peers that have already received an initial image).

Parameters:

message - The message to be published. This may be an image or an update.

publishMappingMessage

void publishMappingMessage(MappingMessage mappingMessage)

Publishes a message that instructs the peer that it should request a different subject and map the updates across.

Parameters:

mappingMessage - The message.

publishSubjectErrorEvent

void publishSubjectErrorEvent(SubjectErrorEvent subjectErrorEvent)

Publishes to all peers subscribed to a subject an event detailing an error in the subscription for that subject. Typically a DataProvider will use this to notify the remote peers that the data they are subscribed to is no longer available.

Parameters:

subjectErrorEvent - The error event to be published.

publishSubjectStatusEvent

void publishSubjectStatusEvent(SubjectStatusEvent subjectStatusEvent)

Publishes to all subscribed peers an event about the change in status of a subject.

Parameters:

subjectStatusEvent - The subject status event to be published.