com.yimidida.shards.strategy.exit.impl.AvgResultsExitOperation.java Source code

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Here is the source code for com.yimidida.shards.strategy.exit.impl.AvgResultsExitOperation.java

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/*
 * @(#)AvgResultsExitOperation.java 2012-8-1 ?10:00:00
 *
 * Copyright (c) 2011-2012 Makersoft.org all rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 *
 */
package com.yimidida.shards.strategy.exit.impl;

import java.util.Collections;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.yimidida.shards.strategy.exit.ExitOperation;
import com.yimidida.shards.strategy.exit.ExitOperationUtils;
import com.yimidida.shards.utils.Pair;

/**
 * 
 */
public class AvgResultsExitOperation implements ExitOperation {

    private final Log log = LogFactory.getLog(getClass());

    public List<Object> apply(List<Object> results) {
        List<Object> nonNullResults = ExitOperationUtils.getNonNullList(results);
        Double total = null;
        int numResults = 0;
        for (Object result : nonNullResults) {
            /**
             * We expect all entries to be Object arrays. the first entry in the
             * array is the average (a double) the second entry in the array is
             * the number of rows that were examined to arrive at the average.
             */
            Pair<Double, Integer> pair = getResultPair(result);
            Double shardAvg = pair.first;
            if (shardAvg == null) {
                // if there's no result from this shard it doesn't go into the
                // calculation. This is consistent with how avg is implemented
                // in the database
                continue;
            }
            int shardResults = pair.second;
            Double shardTotal = shardAvg * shardResults;
            if (total == null) {
                total = shardTotal;
            } else {
                total += shardTotal;
            }
            numResults += shardResults;
        }
        if (numResults == 0 || total == null) {
            return Collections.singletonList(null);
        }
        return Collections.<Object>singletonList(total / numResults);
    }

    private Pair<Double, Integer> getResultPair(Object result) {
        if (!(result instanceof Object[])) {
            final String msg = "Wrong type in result list.  Expected " + Object[].class + " but found "
                    + result.getClass();
            log.error(msg);
            throw new IllegalStateException(msg);
        }
        Object[] resultArr = (Object[]) result;
        if (resultArr.length != 2) {
            final String msg = "Result array is wrong size.  Expected 2 " + " but found " + resultArr.length;
            log.error(msg);
            throw new IllegalStateException(msg);
        }
        return Pair.of((Double) resultArr[0], (Integer) resultArr[1]);
    }

}