A Java Enterprise Edition (Java EE) application usually connects to the database by either making a direct connection to the database using JDBC thin drivers provided by the database vendor or creating a pool of database connections within the Java EE container using the JDBC drivers.
If the application directly connects to the database, then on calling the close() method on the connection object, the database connection closes and the associated Statement and ResultSet objects close and are garbage collected.
If a connection pool is used, a request to the database is made using one of the existing connections in the pool. In this case, on calling close() on the connection object, the database connection returns to the pool. So merely closing the connection does not automatically close the ResultSet and Statement objects. As a result, ResultSet and Statement will not become eligible for garbage collection, as they continue to remain tagged with the database connection in the connection pool.
So make sure you're closing the statements and resultsets that you've retrieved from the connection that you're about to close.
Difference in JDBC connection close and connection pool Connection close