MySQL ResultSet scrollable/updatable not working as expected

Question

I have a test JDBC program that tries to alter the Scrollability and Updatability features of a ResultSet. Unfortunately, all the combinations of TYPE_ and CONCUR_ seem to produce the same result (TYPE_SCROLL_INSENSITIVE and CONCUR_READ_ONLY).

Even with the default (TYPE_FORWARD_ONLY) it's possible to scroll through the ResultSet. Can anyone explain why this is?

I am using MySQL 5.6 and JDK7. Here is the code:

public class ResultSetTest3 {

    public static void main(String[] args)
    {
        Connection conn;

        try {
            conn = DriverManager.getConnection("jdbc:mysql://localhost/bd", "user", "password");

            Statement sta = conn.createStatement();
            sta.execute("DELETE FROM test");
            sta.close();

            PreparedStatement ps = conn.prepareStatement("INSERT INTO test VALUES(?, ?)");
            for(int i=1; i<=100; i++)
            {
                ps.setInt(1, i);
                ps.setString(2, "Teste " + i);
                ps.addBatch();
            }
            ps.executeBatch();
            ps.close();

            System.out.println("TYPE_FORWARD_ONLY  CONCUR_READ_ONLY");
            result(conn, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
            System.out.println("===================================");

            System.out.println("TYPE_SCROLL_INSENSITIVE  CONCUR_READ_ONLY");
            result(conn, ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
            System.out.println("===================================");

            System.out.println("TYPE_SCROLL_SENSITIVE  CONCUR_READ_ONLY");
            result(conn, ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY);
            System.out.println("===================================");

            System.out.println("TYPE_FORWARD_ONLY  CONCUR_UPDATABLE");
            result(conn, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_UPDATABLE);
            System.out.println("===================================");

            System.out.println("TYPE_SCROLL_INSENSITIVE  CONCUR_UPDATABLE");
            result(conn, ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
            System.out.println("===================================");

            System.out.println("TYPE_SCROLL_SENSITIVE  CONCUR_UPDATABLE");
            result(conn, ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
            System.out.println("===================================");

            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    private static void result(Connection conn, int type, int update) throws SQLException
    {
        Statement sta = conn.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
        ResultSet rs = sta.executeQuery("SELECT * FROM test");

        System.out.println(rs.getConcurrency() + " " + update);
        System.out.println(rs.getType() + " " + type);

        try
        {
            rs.absolute(10);
            System.out.println(rs.getInt(1) + " - " + rs.getString(2));

            rs.relative(20);
            System.out.println(rs.getInt(1) + " - " + rs.getString(2));

            rs.previous();
            System.out.println(rs.getInt(1) + " - " + rs.getString(2));

            rs.first();
            System.out.println(rs.getInt(1) + " - " + rs.getString(2));

            try {
                System.out.println("AGORA!!!");
                Thread.sleep(20000);
            } catch (Exception e) {
                System.out.println(e);
            }
            rs.absolute(3);
            System.out.println(rs.getInt(1) + " - " + rs.getString(2));
        }
        catch(SQLException e)
        {
            System.out.println("Not Scrollable");
        }

        try
        {
            rs.next();
            rs.next();
            rs.next();
            rs.next();

            rs.deleteRow();

            rs.next();
            rs.updateString(2, "TesteUpdate");

            rs.insertRow();
        }
        catch(SQLException e)
        {
            System.out.println("Not Updatable");
        }

        rs.close();
        sta.close();
    }
}

Answer 1

As Mark Rotteveel mentions in a comment to the question, MySQL caches ResultSet data by default (also discussed in a blog article by Ben J. Christensen here). An apparent side-effect of this caching is that MySQL Connector/J will "upgrade" a TYPE_FORWARD_ONLY ResultSet to actually be scrollable:

Statement s = dbConnection.createStatement(
        ResultSet.TYPE_FORWARD_ONLY, 
        ResultSet.CONCUR_READ_ONLY);
ResultSet rs = s.executeQuery("SELECT * FROM testdata");
rs.last();
System.out.println(String.format("Current row number: %d", rs.getRow()));
rs.previous();
System.out.println(String.format("Current row number: %d", rs.getRow()));

displays

Current row number: 3
Current row number: 2

According to the blog article cited above, the way to prevent caching and "stream" the ResultSet data is to use Statement.setFetchSize:

Statement s = dbConnection.createStatement(
        ResultSet.TYPE_FORWARD_ONLY, 
        ResultSet.CONCUR_READ_ONLY);
s.setFetchSize(Integer.MIN_VALUE);
ResultSet rs = s.executeQuery("SELECT * FROM testdata");
rs.next();
System.out.println("Data from first row: " + rs.getString(2));
System.out.println("now let's try rs.last() ...");
try {
    rs.last();
    System.out.println("... Okay, done.");
} catch (Exception e) {
    System.out.println("... Exception: " + e.getMessage());
}

resulting in

Data from first row: Gord
now let's try rs.last() ...
... Exception: Operation not supported for streaming result sets