Connections to are resources external to an application, and the garbage collector will not close them automatically.

To close a Statement, ResultSet, or Connection object that is not declared in a try-with-resources statement, use its close method. If auto-commit is disabled, you must explicitly commit or roll back active transactions before you close the connection.

Statements, result sets, and connections extend AutoCloseable in JDK 7 and after. If you declare a connection in a try-with-resources statement and there is an error that the code does not catch, the JRE will attempt to close the connection automatically.

Note that a transaction-severity or higher exception causes to abort an in-flight transaction. But a statement-severity exception does NOT roll back the transaction. Also note that throws an exception if an attempt is made to close a connection with an in-flight transaction. Suppose now that a Connection is declared in a try-with-resources statement, a transaction is in-flight, and an unhandled statement-severity error occurs inside the try-with-resources block. In this situation, will raise a follow-on exception as the JRE exits the try-with-resources block. (For details on error severity levels, see the documentation of the derby.stream.error.logSeverityLevel property in the .)

It is therefore always best to catch errors inside the try-with-resources block and to either roll back or commit, as appropriate, to ensure that there is no pending transaction when leaving the try-with-resources block. This action also improves application portability, since DBMSs differ in their semantics when trying to close a connection with a pending transaction.