How to get row count using ResultSet in Java?

Question

I'm trying to create a simple method that receives a ResultSet as a parameter and returns an int that contains the row count of the ResultSet. Is this a valid way of doing this or not so much?

int size = 0;
    try {
        while(rs.next()){
            size++;
        }
    }
    catch(Exception ex) {
        System.out.println("------------------Tablerize.getRowCount-----------------");
        System.out.println("Cannot get resultSet row count: " + ex);
        System.out.println("--------------------------------------------------------");
    }

I tried this:

int size = 0;
try {
    resultSet.last();
    size = resultSet.getRow();
    resultSet.beforeFirst();
}
catch(Exception ex) {
    return 0;
}
return size;

But I got an error saying

com.microsoft.sqlserver.jdbc.SQLServerException: 
The requested operation is not supported on forward only result sets.

Answer 1

If you have access to the prepared statement that results in this resultset, you can use

connection.prepareStatement(sql, 
  ResultSet.TYPE_SCROLL_INSENSITIVE, 
  ResultSet.CONCUR_READ_ONLY);

This prepares your statement in a way that you can rewind the cursor. This is also documented in the ResultSet Javadoc

In general, however, forwarding and rewinding cursors may be quite inefficient for large result sets. Another option in SQL Server would be to calculate the total number of rows directly in your SQL statement:

SELECT my_table.*, count(*) over () total_rows
FROM my_table
WHERE ...