Why not close the physical connection after obtaining the connection from the database connection pool and calling close?

The database connection pool provider actually repacks common JDBC classes, such as connecton and statement.
The main adapter mode is used. For example, the connnection obtained from the database connection pool may be a java. SQL. Connection
Interface Class, so the close () operation after we use the connection is actually close to this implementation class.
The close implemented in the implementation class does not close the physical connection of the database, but returns it to the connection pool.