Implement AutoCloseable in JDBC connection classes

[rgala]

Added AutoCloseable implementation to JDBC connection classes so they can be used in try-with-resources blocks.

[NicolaIsotta]

Are you sure this actually needed? java.sql.Connection already implements AutoCloseable, while PooledConnection doesn't implement AutoCloseable by design (closing is handled by the pool manager)

[rgala]

PooledCnnection class supports close() method which does not really close the connection but returns it to the pool. With AutoCloseable support it would be possible to obtain pooled connections in try-with-resources blocks and return them to the pool automatically without a need of calling close() method explicitly.

[NicolaIsotta]

Sorry but I don't agree - even the PooledConnection's javadoc state that the close method shouldn't be called by the application.

[rgala]

Then why was this method implemented in AS400JDBCPooledConnection class?

Here is a sample code from IBM directly and as you can see, close method is called to return connection to the pool and AFAIK this is the only way to do it - https://www.ibm.com/docs/en/i/7.6.0?topic=classes-as400jdbcconnectionpool

I am confused with Oracle's documentation, it says that applications never call close method directly, but then:

When an application closes a connection, it calls the Connection method close. When connection pooling is being done, the connection pool manager is notified because it has registered itself as a ConnectionEventListener object using the ConnectionPool method addConnectionEventListener. The connection pool manager deactivates the handle to the PooledConnection object and returns the PooledConnection object to the pool of connections so that it can be used again. Thus, when an application closes its connection, the underlying physical connection is recycled rather than being closed.

[NicolaIsotta]

The IBM example uses Connection, not PooledConnection.

PooledConnection are not meant to be used by final applications, that's the key point and the reason the class doesn't implement AutoCloseable.