Question

Does closing a java.sql.Connection also close all the statements, prepared statements, etc. obtained from that connection? Or is there going to be memory leak if I close the connection but leave the statements, etc. unclosed?

Answer 1

Does closing a java.sql.Connection
also close all the statements,
prepared statements, etc. obtained
from that connection? Or is there
going to be memory leak if I close the
connection but leave the statements,
etc. unclosed?

You should not depend on it.

The spec reads as follows:

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.

The best practice is to close ALL ResultSets, Statements, and Connections in a finally block, each enclosed in their own try/catch, in reverse order of acquisition.

Write a class like this:

public class DatabaseUtils
{
    public static void close(Statement s)
    {
        try
        {
            if (s != null)
            {
                s.close();
            }
        }
        catch (SQLException e)
        {
            // log or report in someway
            e.printStackTrace();
        }
    }

    // similar for ResultSet and Connection
}

Call like this:

Statement s;
try
{
    // JDBC stuff here
}
finally
{
    DatabaseUtils.close(s);
}