Let's put it this way. Say, setting up DataSource/XADataSource mapping to Oracle database is an example of implementing JCA architecture in J2EE.
Here, the ressource adapter is impelemented by Oracle through proper
JDBC drivers. If we dig deeper into the App servers datasource implementation, we can see clues using JCA features like ManagedConnection, ConnectionFactory, ects.
To me, JCA is much like a framework to create pluggable and portable connectors to EIS inside App Servers. The EIS could be an Oracle database or a SAP ERP.
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