Hadoop中Partitoner类原理的讲解

package hadoop;

/**
 * @ClassName HadoopUtils
 * @Description Hadoop中的Partitioner类的讲解说明
 * @Author Administrator
 * @Date 2019/7/10 10:36
 * @Version 1.0
 **/
public class HadoopUtils {

    /**
     * 计算当前月份+星期得到的索引应该分配到哪个reducers节点上
     * @param month 月份
     * @param dayOfWeek 一周中的哪天
     * @param indexRange 索引的范围
     * @param noOfReducers reducers的数量
     */
    public static int getPartition(int month, int dayOfWeek, int indexRange, int noOfReducers) {
        int indicesPerReducer = (int) Math.floor(indexRange / noOfReducers);//Math.floor(11.5)=11
        int index = (month - 1) * 7 + (7 - dayOfWeek);

        /**
         * 索引的范围小于reducers的数量
         */
        if (indexRange < noOfReducers) {
            return index;
        }

        /**
         * 计算当前月份+星期得到的索引应该分配到哪个reducers节点上
         */
        for (int i = 0; i < noOfReducers; i++) {
            int minValForPartitionInclusive = (i) * indicesPerReducer;
            int maxValForPartitionExclusive = (i + 1) * indicesPerReducer;
            if (index >= minValForPartitionInclusive && index < maxValForPartitionExclusive) {
                return i;
            }
        }
    }
}