user manual

Chapter 26: VisiConnect overview 275
System Contracts
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Find the right connection to an EIS from an existing set of pooled
connections, and reuse that connection.
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Hook in Borland Enterprise Server's transaction and security management.
The Borland Enterprise Server establishes, configures, caches and reuses
connections to the EIS automatically through VisiConnect.
The application component performs a lookup of a Resource Adapter
connection factory in the JNDI namespace, using the connection factory to get
a connection to the underlying EIS. The connection factory delegates the
connection creation request to the VisiConnect connection manager instance.
On receiving this request, the connection manager performs a lookup in the
connection pool. If there is no connection in the pool that can satisfy the
connection request, VisiConnect uses the ManagedConnectionFactory
implemented by the Resource Adapter to create a new physical connection to
the underlying EIS. If VisiConnect finds a matching connection in the pool, it
then uses the matching ManagedConnection instance to satisfy the connection
request. If a new ManagedConnection instance is created, the server adds the
new ManagedConnection instance to the connection pool.
VisiConnect registers a ConnectionEventListener with the ManagedConnection
instance. This listener enables VisiConnect to receive event notifications
related to the state of the ManagedConnection instance. VisiConnect uses
these notifications to manage connection pooling, transactions, connection
cleanup and handle error conditions.
VisiConnect uses the ManagedConnection instance to provide a Connection
instance that acts as an application-level handle to the underlying physical
connection, to the application component. The component in turn uses this
handle - and not the underlying physical connection directly - to access EIS
resources.
Transaction Management
Transactional access to multiple EISs is an important and often critical
requirement for enterprise applications. The Connectors supports transaction
access to multiple, heterogeneous EISs - where a number of interactions must
be committed together, or not at all, in order to maintain data consistency and
integrity.
VisiConnect utilizes the Borland Enterprise Server's transaction manager and
supports Resource Adapters conforming to the following transaction support
levels.
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No Transaction support: if a Resource Adapter supports neither Local
Transactions nor XA Transactions, it is non-transactional. If an application
component uses a non-transactional Resource Adapter, the application
component must not involve any connections to the respective EIS in a
transaction. If the application component is required to involve EIS
connections in a transaction, the application component must use a
Resource Adapter which support Local or XA Transactions.