Question on closing ResultSets

[Chris Cano]

According to the Javadocs for ResultSet,

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

Why, then, do I keep seeing examples like this?

Connection con = DriverManager.getConnection(
    "jdbc:somejdbcvendor:other data needed by some jdbc vendor",
    "myLogin",
    "myPassword" );
PreparedStatement stmt = null;
ResultSet rs = null;
try {
    stmt = con.prepareStatement(query);
    rs = stmt.executeQuery();
    while(rs.next()) {
        doStuff();
    }
}
catch (SQLException e) {
    doErrorStuff();
}
finally {
    if(rs != null) {
        try {
            rs.close();
        }
        catch (SQLException e) {}
    }
    if(stmt != null) {
        try {
            stmt.close();
        }
        catch (SQLException e) {}
    }
    if(con != null) {
        try {
            con.close();
        }
        catch (SQLException e) {}
    }
}

Isn't closing the ResultSet superfluous, since the Statement is being closed right afterwards?

[Jeanne Boyarsky]

Chris Cano wrote:Isn't closing the ResultSet superfluous, since the Statement is being closed right afterwards?

Yes. However some drivers don't implement the spec properly so people got in the habit of closing both. I do the same. No harm in it.

[Chris Cano]

Alright, thanks.

How about the part about when the Statement is re-executed? If I have a PreparedStatement executing a query in a loop (or just any reuse of a PreparedStatement), do I need to close the ResultSet from each execution of the PreparedStatement?

[Scott Selikoff]

You should close the result set if you are going to reuse a statement. While not closing it won't kill your application, if the life of the statement is significantly long, you could end up with a lot of unclosed result sets. Keep in mind, garbage collection will not close an object. As Jeanne pointed out, though, you should always close both when you're done with them since you can't predict what a driver is going to do and because its a good practice. Not closing JDBC objects properly can lead to a lot of bugs as an application scales to more and more users.

I wrote an article about closing JDBC objects a few years back you might find of use.