MeanReducer.java

package backtype.storm.metric.api;

import backtype.storm.metric.api.IReducer;

class MeanReducerState {
	public int count = 0;
	public double sum = 0.0;
}

public class MeanReducer implements IReducer<MeanReducerState> {
	public MeanReducerState init() {
		return new MeanReducerState();
	}

	public MeanReducerState reduce(MeanReducerState acc, Object input) {
		acc.count++;
		if (input instanceof Double) {
			acc.sum += (Double) input;
		} else if (input instanceof Long) {
			acc.sum += ((Long) input).doubleValue();
		} else if (input instanceof Integer) {
			acc.sum += ((Integer) input).doubleValue();
		} else {
			throw new RuntimeException(
					"MeanReducer::reduce called with unsupported input type `"
							+ input.getClass()
							+ "`. Supported types are Double, Long, Integer.");
		}
		return acc;
	}

	public Object extractResult(MeanReducerState acc) {
		if (acc.count > 0) {
			return new Double(acc.sum / (double) acc.count);
		} else {
			return null;
		}
	}
}