Processing Rows in Batches

import java.util.*;

/**
* Collects the N rows with the largest key 
* values from a ResultSet. This version is 
* hard-wired to expect a String in column 1, 
* and sort key is an int in column 2.
* @author slott
*/
public class TopNRows {
    /** Number of rows to keep */
    int keep;
    /** Set of top N rows */                               <b>(1)</b>
    TreeMap topRows;
    /**
    * Creates a new instance of TopNRows.
    * @param keep int top number of values to keep.
    */
    public TopNRows( int keep ) {
        this.keep= keep;
    }
    /**
    * Scans the given result set, checking column 2, the integer key,
    * for the largest value.
    * @param rs ResultSet to scan
    */
    public void scan( ResultSet rs ) {
        topRows= new TreeMap();
        while( rs.next() ) {
            Integer rowKey= new Integer(rs.getInt(2));      <b>(2)</b>
            if( topRows.size() <= keep ) {
              topRows.put( rowKey, rs.getString(1) );
              continue;
            }
            Integer minKeepKey= (Integer)topRows.firstKey(); <b>(3)</b>
            if( rowKey.compareTo( minKeepKey ) > 0 ) {
                topRows.remove( minKeepKey );
                topRows.put( rowKey, rs.getString(1) );
            }
        }
    }
    /**
    * Returns an iterator over the selected results.
    * These will be Map.Entry objects. 
    * The key will be column 2 values, transformed to Integers. 
    * The entry will be column 1 values, still Strings.
    * @return Iterator over the Map.
    */
    public Iterator iterator( ) {
        return topRows.entrySet().iterator();
    }
}

Example 4: Fast Java fetch.