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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: Not closing a SQL(ite3) connection
Date: Sat, 12 Aug 2017 10:00:46 +0200
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Arne Vajhøj <arne@vajhoej.dk> writes:

> On 8/11/2017 4:26 AM, Cecil Westerhof wrote:
>> I have a strange problem. I made a class SQLite3ResultSet. There is a
>> lot of stuff to be removed, but that is just to find out if it is
>> doing what I think it is doing.

You did not read this part?


>> And the close method is (for now, because I want to test it):

And also not this?


>>      @Override
>>      public void close() throws SQLite3Exception {
>>          System.out.println("SQLite3ResultSet: closing open resources.");
>>          String    errorMsg  = "";
>>
>>          try {
>>              stmt.close();
>>              resultSet.next();
>>              resultSet.close();
>
> resultSet.close();
> stmt.close();
>
> was rather obvious.

If you read my message a bit better, you would have seen that it is
not real code, but that I do things that are wrong to verify that the
good code does what I think it does.


>>          } catch (SQLException e) {
>>              errorMsg += "Could not close ResultSet.\n";
>>              System.out.println(errorMsg);
>>          }
>>          System.out.println("Closed resultSet.");
>>          try {
>>              stmt.close();
>>          } catch (SQLException e) {
>>              errorMsg += "Could not close Statement belonging to ResultSet.\n";
>>              System.out.println(errorMsg);
>>          }
>>          System.out.println("closed stmt");
>>          System.out.println("SQLite3ResultSet: closed open resources.");
>>          if (!errorMsg.isEmpty()) {
>>              throw new SQLite3Exception(errorMsg);
>>          }
>>      }
>>
>> In the first try I close the stmt and then I do a resultSet.next(). I
>> would expect an exception, because I closed the stmt, but I do not get
>> an exception. Why not?
>
> There is nothing in documentation for next() requiring an exception to
> be thrown (ResultSet is not closed and it may not get a database error -
> maybe it does not even talk to the database).

That was the problem. When using:
    resultSet.getInt("Count");
instead of:
    resultSet.next();

I get the error I expected.


Now I can remove the stmt field out of my class.

With this I verified that I did not get a Statement leak:
    @Override
    public void close() throws SQLite3Exception {
        System.out.println("SQLite3ResultSet: closing open resources.");
        try {
            Statement stmt = resultSet.getStatement();

            stmt.close();
            System.out.println("Closed stmt.");
            resultSet.getInt("Count");
            System.out.println("Did getInt");
            resultSet.close();
        } catch (SQLException e) {
            throw new SQLite3Exception("Could not close ResultSet.");
        }
        System.out.println("Closed resultSet.");
    }

I do get ‘Closed stmt, but I do not get ‘Did getInt’. So the closing
of stmt works.

The real method is now:
    @Override
    public void close() throws SQLite3Exception {
        boolean closedResultSet = false;

        try {
            Statement stmt = resultSet.getStatement();

            resultSet.close();
            stmt.close();
        } catch (SQLException e) {
            if (closedResultSet) {
                throw new SQLite3Exception("Could not close Statement after closing ResultSet.");
            }
            throw new SQLite3Exception("Could not close ResultSet.");
        }
        System.out.println("Closed resultSet.");
    }

The reason that I wrote this code was that I do not want to have to
put a Statement and a ResultSet into my try with resources.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof