Question

What happens with the statement when result set is closed?

    Statement stmt = null;
    ResultSet rs = null;

    try {
        stmt = con.createStatement();
        rs = stmt.executeQuery(query.toString());
        ...
    }

    // lots of code

    rs.close()

Note: A ResultSet object is automatically closed by the Statement
object that generated it when that Statement object is closed,
re-executed, or is used to retrieve the next result from a sequence of
multiple results.

But what happens when ResultSet is closed first?

For what matter, what should happen first?

Answer 1

You should close the objects in the reverse order of creating them.
So first, the ResultSet, then the Statement and in the end, Connection.

If you don’t close the Statement it stays open and you can execute another query with it (if it’s a PreparedStatement or CallableStatement you are able to change query parameters).

Also note, that what you quoted is a JDBC specification, and the implementation of it is up to a JDBC driver provider. Usually, you should not trust them, and manually close those objects.

The other thing – I think more important – if you are using connection pools (like on JBoss), closing connection just releases it back to the pool, and the underlying objects are not released. And because of this, its recommended to always manually release all the objects you created.