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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: Is this the way to work with try with resources
Date: Wed, 09 Aug 2017 23:17:11 +0200
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Cecil Westerhof <Cecil@decebal.nl> writes:

> Andreas Leitgeb <avl@logic.at> writes:
>
>> Cecil Westerhof <Cecil@decebal.nl> wrote:
>>> I had there the following function:
>>>     public ResultSet executeQuery(String query) throws SQLException {
>>>         return conn.createStatement().executeQuery(query);
>>>     }
>>> but I now changed that to:
>>>     public ResultSet executeQuery(String query) throws SQLException {
>>>         try (Statement stmt = conn.createStatement()) {
>>>             return stmt.executeQuery(query);
>>>         }
>>>     }
>>> This should take care of the leakage.
>>
>> I fear, next trouble is right ahead.
>>
>> try doesn't only close it's resource on failure, but also on completion!
>>
>> That means, it will (because closing the statement will also close the
>> ResultSet) return an already closed ResultSet.
>
> I have in my code:
>     private static void displayOldestUsed() {
>         try (ResultSet rsOldest = sqlite3Conn.executeQuery(OLDEST_USED)) {
>             if (rsOldest.next()) {
>                 giveMessage("Oldest used: " + rsOldest.getString("used") + ".");
>             }
>         } catch (SQLException e) {
>             giveError("Error in displayOldestUsed");
>             e.printStackTrace();
>             fatalError("");
>         }
>     }
>
> And rsOldest.getString("used") gives the result I would expect. Or am
> I just ‘lucky’?

Nope, I did something wrong. When doing it right I got:
    java.sql.SQLException: ResultSet closed

So I know do it with Statement and ResultSet in the try with
resources. Makes my SQLite3 class a bit less useful.

But my statistics is now:
    private static void statistics() {
        try  {
            int    count;
            String format;
            int    maxLen;

            count  = sqlite3Conn.getCount(COUNT_TOTAL_PROV);
            // First count is the largest
            maxLen = String.format("%,d", count).length();
            format = "There are %," + maxLen + "d %-6s proverbs.";
            giveMessage(String.format(format, count, "total"));
            count  = sqlite3Conn.getCount(COUNT_UNUSED_PROV);
            if (count != 0) {
                giveMessage(String.format(format, count, "unused"));
            }
            count  = sqlite3Conn.getCount(COUNT_USED_PROV);
            giveMessage(String.format(format, count, "used"));
        } catch (SQLException e) {
            giveError("Error in statistics");
            e.printStackTrace();
            fatalError("");
        }
    }

Because I defined:
    public int getCount(String query) throws SQLException {
        int count;

        try (Statement stmt     = createStatement();
            ResultSet  rsCount  = stmt.executeQuery(query)) {
            count = rsCount.getInt("count");
        }
        return count;
    }

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