12.6.1.2 Communication Layer

• Introduction

• Interfaces and Usage

Introduction

Communication between the Central Server and Distributed Mediation Servers can be operated in one-way or two-way modes, these modes are explained in Communication Mechanism. One-way communication mode is initiated and maintained only by the Distributed Mediation Servers and so, the communication is established and persists only for the time the data is transferred to the Central Server. On the other hand, two-way communication mode is maintained by both the Central and Distributed Mediation Server and so, the communication is persistent.

Interfaces and Usage

Communication customization is controlled by two interfaces namely, SPPCommInitIfc and SPPRegionalCommIfc. These interfaces have to be implemented at the Central Server and Distributed Regional Server respectively. The CommunicationInfo.xml present in the conf directory of the respective servers decides what kind of communication will exist between the Central Server and the Distributed Mediation Servers.

SPPCommInitIfc interface is implemented for establishing the communication link. The methods provided by this interface are init(), open() and shutdown(). A CommunicationException is thrown if there are any errors.

• The init() method is invoked before the communication is established. This method can be used to perform any pre-initialization actions. The argument to this method is a Properties object containing the MainProps and UserProps values obtained from CommunicationInfo.xml configuration file.

• The open() method is invoked to create an instance of the communication session object. This method is very important as this method instantiates the actual implementation for read and write.

• At the Central Server, the open() method waits infinitely to listen for any Distributed Mediation Server to connect. When a Distributed Mediation Server connection is established , the instance of SPPRegionalCommIfc interface implementation is returned.

• At the Distributed Mediation Server, the open method checks whether the connection is successful and returns the instance of SPPRegionalCommIfc interface implementation.

The argument to this method is a Properties object containing the MainProps and UserProps values obtained from CommunicationInfo.xml configuration file.

• The shutdown() method is invoked to close the communication.

SPPRegionalCommIfc interface implements the protocol specific logic for data transfer. The methods provided by this interface are initialize(),  write(), read() and shutdown(). A communication exception is thrown if there are any errors.

• The initialize() method is invoked to perform initialization of protocol to be used for data transfer. The argument to this method is a Properties object containing the values necessary for establishing the communication session. This method returns true if the initialization is successful, else returns false.

• The write() method is invoked whenever data is to be sent to the counterpart server. The write interval present in CommunicationInfo.xml determines the time interval at which this method is invoked. The argument to this method is a DataObject that contains the data that is to be sent to the counterpart server. This method throws CommunicationException if the write operation is not successful.

• The read() method is invoked whenever data is to be read from the counterpart server. The read interval present in CommunicationInfo.xml determines the time interval at which this method is invoked. This method returns the DataObject received from the counterpart server.

• The shutdown() method is invoked to close the communication and release the resources.