Re: Will calling "close()" on a "java.sql.Connection" really close
associated resources?
david.karr wrote:
In billions of lines of code using JDBC connections, I constantly see
finally clauses that first close a ResultSet, then a Statement, and
then a Connection (if any of them are non-null). The thing is, the
javadoc for the "close()" method says this:
"Releases this Connection object's database and JDBC resources
immediately instead of waiting for them to be automatically released.
"
That implies to me that manually closing the ResultSet and Statement
just before closing the Connection is a waste of perfectly good
bytecode.
If I'm understanding this correctly, is there any situation where it's
still a good idea to manually close the resources when you're about to
close the connection?
JDBC spec says:
<quote>
9.4.4 Closing Connection Objects
An application calls the method Connection.close to indicate that it has
finished
using a connection. All Statement objects created from a given
Connection object
will be closed when the close method for the object is called.
Once a Connection has been closed, any attempt to access any of its
methods with
the exception of the close, isClosed or isValid methods will result in a
SQLException being thrown.
</quote>
<quote>
13.1.4 Closing Statement Objects
An application calls the method Statement.close to indicate that it has
finished
processing a statement. All Statement objects will be closed when the
connection
that created them is closed. However, it is good coding practice for
applications to
close statements as soon as they have finished processing them. This
allows any
external resources that the statement is using to be released immediately.
Closing a Statement object will close and invalidate any instances of
ResultSet
produced by that Statement object. The resources held by the ResultSet
object
may not be released until garbage collection runs again, so it is a good
practice to
explicitly close ResultSet objects when they are no longer needed.
Once a Statement has been closed, any attempt to access any of its
methods with
the exception of the isClosed or close methods will result in a SQLException
being thrown.
These comments about closing Statement objects apply to PreparedStatement
and CallableStatement objects as well.
</quote>
So they will be closed.
But actually I think it is good to do it explicit. Because
it makes it obvious that they are being closed also to those
that have not read the JDBC spec.
Readable code is better than short code.
Arne