MkFieldsGrouper.java

package org.act.tstream.task.group;

import java.util.Iterator;
import java.util.List;

import backtype.storm.tuple.Fields;

import org.act.tstream.utils.JStormUtils;

/**
 * field grouping
 * 
 * @author yannian
 * 
 */
public class MkFieldsGrouper {
	private Fields out_fields;
	private Fields group_fields;
	private List<Integer> out_tasks;

	public MkFieldsGrouper(Fields _out_fields, Fields _group_fields,
			List<Integer> _out_tasks) {

		for (Iterator<String> it = _group_fields.iterator(); it.hasNext();) {
			String groupField = it.next();

			// if groupField isn't in _out_fields, it would throw Exception
			_out_fields.fieldIndex(groupField);
		}

		this.out_fields = _out_fields;
		this.group_fields = _group_fields;
		this.out_tasks = _out_tasks;

	}

	public List<Integer> grouper(List<Object> values) {
		int hashcode = this.out_fields.select(this.group_fields, values)
				.hashCode();
		int group = Math.abs(hashcode % this.out_tasks.size());
		return JStormUtils.mk_list(out_tasks.get(group));
	}
}